Add basic infrastructure to support the FWFT extension in KVM.

Signed-off-by: Clément Léger <cleger@rivosinc.com>
---
 arch/riscv/include/asm/kvm_host.h          |   4 +
 arch/riscv/include/asm/kvm_vcpu_sbi.h      |   1 +
 arch/riscv/include/asm/kvm_vcpu_sbi_fwft.h |  37 ++++
 arch/riscv/include/uapi/asm/kvm.h          |   1 +
 arch/riscv/kvm/Makefile                    |   1 +
 arch/riscv/kvm/vcpu_sbi.c                  |   4 +
 arch/riscv/kvm/vcpu_sbi_fwft.c             | 187 +++++++++++++++++++++
 7 files changed, 235 insertions(+)
 create mode 100644 arch/riscv/include/asm/kvm_vcpu_sbi_fwft.h
 create mode 100644 arch/riscv/kvm/vcpu_sbi_fwft.c

diff --git a/arch/riscv/include/asm/kvm_host.h b/arch/riscv/include/asm/kvm_host.h
index bb93d2995ea2..c0db61ba691a 100644
--- a/arch/riscv/include/asm/kvm_host.h
+++ b/arch/riscv/include/asm/kvm_host.h
@@ -19,6 +19,7 @@
 #include <asm/kvm_vcpu_fp.h>
 #include <asm/kvm_vcpu_insn.h>
 #include <asm/kvm_vcpu_sbi.h>
+#include <asm/kvm_vcpu_sbi_fwft.h>
 #include <asm/kvm_vcpu_timer.h>
 #include <asm/kvm_vcpu_pmu.h>
 
@@ -281,6 +282,9 @@ struct kvm_vcpu_arch {
 	/* Performance monitoring context */
 	struct kvm_pmu pmu_context;
 
+	/* Firmware feature SBI extension context */
+	struct kvm_sbi_fwft fwft_context;
+
 	/* 'static' configurations which are set only once */
 	struct kvm_vcpu_config cfg;
 
diff --git a/arch/riscv/include/asm/kvm_vcpu_sbi.h b/arch/riscv/include/asm/kvm_vcpu_sbi.h
index cb68b3a57c8f..ffd03fed0c06 100644
--- a/arch/riscv/include/asm/kvm_vcpu_sbi.h
+++ b/arch/riscv/include/asm/kvm_vcpu_sbi.h
@@ -98,6 +98,7 @@ extern const struct kvm_vcpu_sbi_extension vcpu_sbi_ext_hsm;
 extern const struct kvm_vcpu_sbi_extension vcpu_sbi_ext_dbcn;
 extern const struct kvm_vcpu_sbi_extension vcpu_sbi_ext_susp;
 extern const struct kvm_vcpu_sbi_extension vcpu_sbi_ext_sta;
+extern const struct kvm_vcpu_sbi_extension vcpu_sbi_ext_fwft;
 extern const struct kvm_vcpu_sbi_extension vcpu_sbi_ext_experimental;
 extern const struct kvm_vcpu_sbi_extension vcpu_sbi_ext_vendor;
 
diff --git a/arch/riscv/include/asm/kvm_vcpu_sbi_fwft.h b/arch/riscv/include/asm/kvm_vcpu_sbi_fwft.h
new file mode 100644
index 000000000000..5782517f6e08
--- /dev/null
+++ b/arch/riscv/include/asm/kvm_vcpu_sbi_fwft.h
@@ -0,0 +1,37 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ * Copyright (c) 2025 Rivos Inc.
+ *
+ * Authors:
+ *     Clément Léger <cleger@rivosinc.com>
+ */
+
+#ifndef __KVM_VCPU_RISCV_FWFT_H
+#define __KVM_VCPU_RISCV_FWFT_H
+
+#include <asm/sbi.h>
+
+struct kvm_sbi_fwft_config;
+struct kvm_vcpu;
+
+struct kvm_sbi_fwft_feature {
+	enum sbi_fwft_feature_t id;
+	bool (*supported)(struct kvm_vcpu *vcpu);
+	int (*set)(struct kvm_vcpu *vcpu, struct kvm_sbi_fwft_config *conf, unsigned long value);
+	int (*get)(struct kvm_vcpu *vcpu, struct kvm_sbi_fwft_config *conf, unsigned long *value);
+};
+
+struct kvm_sbi_fwft_config {
+	const struct kvm_sbi_fwft_feature *feature;
+	bool supported;
+	unsigned long flags;
+};
+
+/* FWFT data structure per vcpu */
+struct kvm_sbi_fwft {
+	struct kvm_sbi_fwft_config *configs;
+};
+
+#define vcpu_to_fwft(vcpu) (&(vcpu)->arch.fwft_context)
+
+#endif /* !__KVM_VCPU_RISCV_FWFT_H */
diff --git a/arch/riscv/include/uapi/asm/kvm.h b/arch/riscv/include/uapi/asm/kvm.h
index f06bc5efcd79..fa6eee1caf41 100644
--- a/arch/riscv/include/uapi/asm/kvm.h
+++ b/arch/riscv/include/uapi/asm/kvm.h
@@ -202,6 +202,7 @@ enum KVM_RISCV_SBI_EXT_ID {
 	KVM_RISCV_SBI_EXT_DBCN,
 	KVM_RISCV_SBI_EXT_STA,
 	KVM_RISCV_SBI_EXT_SUSP,
+	KVM_RISCV_SBI_EXT_FWFT,
 	KVM_RISCV_SBI_EXT_MAX,
 };
 
diff --git a/arch/riscv/kvm/Makefile b/arch/riscv/kvm/Makefile
index 4e0bba91d284..06e2d52a9b88 100644
--- a/arch/riscv/kvm/Makefile
+++ b/arch/riscv/kvm/Makefile
@@ -26,6 +26,7 @@ kvm-y += vcpu_onereg.o
 kvm-$(CONFIG_RISCV_PMU_SBI) += vcpu_pmu.o
 kvm-y += vcpu_sbi.o
 kvm-y += vcpu_sbi_base.o
+kvm-y += vcpu_sbi_fwft.o
 kvm-y += vcpu_sbi_hsm.o
 kvm-$(CONFIG_RISCV_PMU_SBI) += vcpu_sbi_pmu.o
 kvm-y += vcpu_sbi_replace.o
diff --git a/arch/riscv/kvm/vcpu_sbi.c b/arch/riscv/kvm/vcpu_sbi.c
index f81f06f82650..3b37deaed4e7 100644
--- a/arch/riscv/kvm/vcpu_sbi.c
+++ b/arch/riscv/kvm/vcpu_sbi.c
@@ -78,6 +78,10 @@ static const struct kvm_riscv_sbi_extension_entry sbi_ext[] = {
 		.ext_idx = KVM_RISCV_SBI_EXT_STA,
 		.ext_ptr = &vcpu_sbi_ext_sta,
 	},
+	{
+		.ext_idx = KVM_RISCV_SBI_EXT_FWFT,
+		.ext_ptr = &vcpu_sbi_ext_fwft,
+	},
 	{
 		.ext_idx = KVM_RISCV_SBI_EXT_EXPERIMENTAL,
 		.ext_ptr = &vcpu_sbi_ext_experimental,
diff --git a/arch/riscv/kvm/vcpu_sbi_fwft.c b/arch/riscv/kvm/vcpu_sbi_fwft.c
new file mode 100644
index 000000000000..fe608bf16558
--- /dev/null
+++ b/arch/riscv/kvm/vcpu_sbi_fwft.c
@@ -0,0 +1,187 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (c) 2025 Rivos Inc.
+ *
+ * Authors:
+ *     Clément Léger <cleger@rivosinc.com>
+ */
+
+#include <linux/errno.h>
+#include <linux/err.h>
+#include <linux/kvm_host.h>
+#include <asm/cpufeature.h>
+#include <asm/sbi.h>
+#include <asm/kvm_vcpu_sbi.h>
+#include <asm/kvm_vcpu_sbi_fwft.h>
+
+static const enum sbi_fwft_feature_t kvm_fwft_defined_features[] = {
+	SBI_FWFT_MISALIGNED_EXC_DELEG,
+	SBI_FWFT_LANDING_PAD,
+	SBI_FWFT_SHADOW_STACK,
+	SBI_FWFT_DOUBLE_TRAP,
+	SBI_FWFT_PTE_AD_HW_UPDATING,
+	SBI_FWFT_POINTER_MASKING_PMLEN,
+};
+
+static bool kvm_fwft_is_defined_feature(enum sbi_fwft_feature_t feature)
+{
+	int i;
+
+	for (i = 0; i < ARRAY_SIZE(kvm_fwft_defined_features); i++) {
+		if (kvm_fwft_defined_features[i] == feature)
+			return true;
+	}
+
+	return false;
+}
+
+static const struct kvm_sbi_fwft_feature features[] = {
+};
+
+static struct kvm_sbi_fwft_config *
+kvm_sbi_fwft_get_config(struct kvm_vcpu *vcpu, enum sbi_fwft_feature_t feature)
+{
+	int i = 0;
+	struct kvm_sbi_fwft *fwft = vcpu_to_fwft(vcpu);
+
+	for (i = 0; i < ARRAY_SIZE(features); i++) {
+		if (fwft->configs[i].feature->id == feature)
+			return &fwft->configs[i];
+	}
+
+	return NULL;
+}
+
+static int kvm_fwft_get_feature(struct kvm_vcpu *vcpu, unsigned long feature,
+				struct kvm_sbi_fwft_config **conf)
+{
+	struct kvm_sbi_fwft_config *tconf;
+
+	/* Feature are defined as 32 bits identifiers */
+	if (feature & ~(BIT_ULL(32) - 1))
+		return SBI_ERR_INVALID_PARAM;
+
+	tconf = kvm_sbi_fwft_get_config(vcpu, feature);
+	if (!tconf) {
+		if (kvm_fwft_is_defined_feature(feature))
+			return SBI_ERR_NOT_SUPPORTED;
+
+		return SBI_ERR_DENIED;
+	}
+
+	if (!tconf->supported)
+		return SBI_ERR_NOT_SUPPORTED;
+
+	*conf = tconf;
+
+	return SBI_SUCCESS;
+}
+
+static int kvm_sbi_fwft_set(struct kvm_vcpu *vcpu, unsigned long feature,
+			    unsigned long value, unsigned long flags)
+{
+	int ret;
+	struct kvm_sbi_fwft_config *conf;
+
+	ret = kvm_fwft_get_feature(vcpu, feature, &conf);
+	if (ret)
+		return ret;
+
+	if ((flags & ~SBI_FWFT_SET_FLAG_LOCK) != 0)
+		return SBI_ERR_INVALID_PARAM;
+
+	if (conf->flags & SBI_FWFT_SET_FLAG_LOCK)
+		return SBI_ERR_DENIED_LOCKED;
+
+	conf->flags = flags;
+
+	return conf->feature->set(vcpu, conf, value);
+}
+
+static int kvm_sbi_fwft_get(struct kvm_vcpu *vcpu, unsigned long feature,
+			    unsigned long *value)
+{
+	int ret;
+	struct kvm_sbi_fwft_config *conf;
+
+	ret = kvm_fwft_get_feature(vcpu, feature, &conf);
+	if (ret)
+		return ret;
+
+	return conf->feature->get(vcpu, conf, value);
+}
+
+static int kvm_sbi_ext_fwft_handler(struct kvm_vcpu *vcpu, struct kvm_run *run,
+				    struct kvm_vcpu_sbi_return *retdata)
+{
+	int ret = 0;
+	struct kvm_cpu_context *cp = &vcpu->arch.guest_context;
+	unsigned long funcid = cp->a6;
+
+	switch (funcid) {
+	case SBI_EXT_FWFT_SET:
+		ret = kvm_sbi_fwft_set(vcpu, cp->a0, cp->a1, cp->a2);
+		break;
+	case SBI_EXT_FWFT_GET:
+		ret = kvm_sbi_fwft_get(vcpu, cp->a0, &retdata->out_val);
+		break;
+	default:
+		ret = SBI_ERR_NOT_SUPPORTED;
+		break;
+	}
+
+	retdata->err_val = ret;
+
+	return 0;
+}
+
+static int kvm_sbi_ext_fwft_init(struct kvm_vcpu *vcpu)
+{
+	struct kvm_sbi_fwft *fwft = vcpu_to_fwft(vcpu);
+	const struct kvm_sbi_fwft_feature *feature;
+	struct kvm_sbi_fwft_config *conf;
+	int i;
+
+	fwft->configs = kcalloc(ARRAY_SIZE(features), sizeof(struct kvm_sbi_fwft_config),
+				GFP_KERNEL);
+	if (!fwft->configs)
+		return -ENOMEM;
+
+	for (i = 0; i < ARRAY_SIZE(features); i++) {
+		feature = &features[i];
+		conf = &fwft->configs[i];
+		if (feature->supported)
+			conf->supported = feature->supported(vcpu);
+		else
+			conf->supported = true;
+
+		conf->feature = feature;
+	}
+
+	return 0;
+}
+
+static void kvm_sbi_ext_fwft_deinit(struct kvm_vcpu *vcpu)
+{
+	struct kvm_sbi_fwft *fwft = vcpu_to_fwft(vcpu);
+
+	kfree(fwft->configs);
+}
+
+static void kvm_sbi_ext_fwft_reset(struct kvm_vcpu *vcpu)
+{
+	int i = 0;
+	struct kvm_sbi_fwft *fwft = vcpu_to_fwft(vcpu);
+
+	for (i = 0; i < ARRAY_SIZE(features); i++)
+		fwft->configs[i].flags = 0;
+}
+
+const struct kvm_vcpu_sbi_extension vcpu_sbi_ext_fwft = {
+	.extid_start = SBI_EXT_FWFT,
+	.extid_end = SBI_EXT_FWFT,
+	.handler = kvm_sbi_ext_fwft_handler,
+	.init = kvm_sbi_ext_fwft_init,
+	.deinit = kvm_sbi_ext_fwft_deinit,
+	.reset = kvm_sbi_ext_fwft_reset,
+};
-- 
2.47.2

On Mon, Feb 10, 2025 at 10:35:47PM +0100, Clément Léger wrote:
>Add basic infrastructure to support the FWFT extension in KVM.
>
>Signed-off-by: Clément Léger <cleger@rivosinc.com>
>---
> arch/riscv/include/asm/kvm_host.h          |   4 +
> arch/riscv/include/asm/kvm_vcpu_sbi.h      |   1 +
> arch/riscv/include/asm/kvm_vcpu_sbi_fwft.h |  37 ++++
> arch/riscv/include/uapi/asm/kvm.h          |   1 +
> arch/riscv/kvm/Makefile                    |   1 +
> arch/riscv/kvm/vcpu_sbi.c                  |   4 +
> arch/riscv/kvm/vcpu_sbi_fwft.c             | 187 +++++++++++++++++++++
> 7 files changed, 235 insertions(+)
> create mode 100644 arch/riscv/include/asm/kvm_vcpu_sbi_fwft.h
> create mode 100644 arch/riscv/kvm/vcpu_sbi_fwft.c
>
>diff --git a/arch/riscv/include/asm/kvm_host.h b/arch/riscv/include/asm/kvm_host.h
>index bb93d2995ea2..c0db61ba691a 100644
>--- a/arch/riscv/include/asm/kvm_host.h
>+++ b/arch/riscv/include/asm/kvm_host.h
>@@ -19,6 +19,7 @@
> #include <asm/kvm_vcpu_fp.h>
> #include <asm/kvm_vcpu_insn.h>
> #include <asm/kvm_vcpu_sbi.h>
>+#include <asm/kvm_vcpu_sbi_fwft.h>
> #include <asm/kvm_vcpu_timer.h>
> #include <asm/kvm_vcpu_pmu.h>
>
>@@ -281,6 +282,9 @@ struct kvm_vcpu_arch {
> 	/* Performance monitoring context */
> 	struct kvm_pmu pmu_context;
>
>+	/* Firmware feature SBI extension context */
>+	struct kvm_sbi_fwft fwft_context;
>+
> 	/* 'static' configurations which are set only once */
> 	struct kvm_vcpu_config cfg;
>
>diff --git a/arch/riscv/include/asm/kvm_vcpu_sbi.h b/arch/riscv/include/asm/kvm_vcpu_sbi.h
>index cb68b3a57c8f..ffd03fed0c06 100644
>--- a/arch/riscv/include/asm/kvm_vcpu_sbi.h
>+++ b/arch/riscv/include/asm/kvm_vcpu_sbi.h
>@@ -98,6 +98,7 @@ extern const struct kvm_vcpu_sbi_extension vcpu_sbi_ext_hsm;
> extern const struct kvm_vcpu_sbi_extension vcpu_sbi_ext_dbcn;
> extern const struct kvm_vcpu_sbi_extension vcpu_sbi_ext_susp;
> extern const struct kvm_vcpu_sbi_extension vcpu_sbi_ext_sta;
>+extern const struct kvm_vcpu_sbi_extension vcpu_sbi_ext_fwft;
> extern const struct kvm_vcpu_sbi_extension vcpu_sbi_ext_experimental;
> extern const struct kvm_vcpu_sbi_extension vcpu_sbi_ext_vendor;
>
>diff --git a/arch/riscv/include/asm/kvm_vcpu_sbi_fwft.h b/arch/riscv/include/asm/kvm_vcpu_sbi_fwft.h
>new file mode 100644
>index 000000000000..5782517f6e08
>--- /dev/null
>+++ b/arch/riscv/include/asm/kvm_vcpu_sbi_fwft.h
>@@ -0,0 +1,37 @@
>+/* SPDX-License-Identifier: GPL-2.0-only */
>+/*
>+ * Copyright (c) 2025 Rivos Inc.
>+ *
>+ * Authors:
>+ *     Clément Léger <cleger@rivosinc.com>
>+ */
>+
>+#ifndef __KVM_VCPU_RISCV_FWFT_H
>+#define __KVM_VCPU_RISCV_FWFT_H
>+
>+#include <asm/sbi.h>
>+
>+struct kvm_sbi_fwft_config;
>+struct kvm_vcpu;
>+


Can we add some comments here for future fwft providers along below lines?

Reason being, patch defaults to `conf->supported = true` if `supported` fn
pointer in `kvm_sbi_fwft_feature` was NULL. Although `kvm_sbi_fwft_set/get`
does get/set fn pointers (it would happen even if `supported` fn pointer
was NULL).

>+struct kvm_sbi_fwft_feature {
>+	enum sbi_fwft_feature_t id;
	/* If function not provided, KVM will default assume to be true */
>+	bool (*supported)(struct kvm_vcpu *vcpu);
	/* Must always provide function pointers for get/set */
>+	int (*set)(struct kvm_vcpu *vcpu, struct kvm_sbi_fwft_config *conf, unsigned long value);
>+	int (*get)(struct kvm_vcpu *vcpu, struct kvm_sbi_fwft_config *conf, unsigned long *value);


>+};
>+
>+struct kvm_sbi_fwft_config {
>+	const struct kvm_sbi_fwft_feature *feature;
>+	bool supported;
>+	unsigned long flags;
>+};
>+
>+/* FWFT data structure per vcpu */
>+struct kvm_sbi_fwft {
>+	struct kvm_sbi_fwft_config *configs;
>+};
>+
>+#define vcpu_to_fwft(vcpu) (&(vcpu)->arch.fwft_context)
>+
>+#endif /* !__KVM_VCPU_RISCV_FWFT_H */
>diff --git a/arch/riscv/include/uapi/asm/kvm.h b/arch/riscv/include/uapi/asm/kvm.h
>index f06bc5efcd79..fa6eee1caf41 100644
>--- a/arch/riscv/include/uapi/asm/kvm.h
>+++ b/arch/riscv/include/uapi/asm/kvm.h
>@@ -202,6 +202,7 @@ enum KVM_RISCV_SBI_EXT_ID {
> 	KVM_RISCV_SBI_EXT_DBCN,
> 	KVM_RISCV_SBI_EXT_STA,
> 	KVM_RISCV_SBI_EXT_SUSP,
>+	KVM_RISCV_SBI_EXT_FWFT,
> 	KVM_RISCV_SBI_EXT_MAX,
> };
>
>diff --git a/arch/riscv/kvm/Makefile b/arch/riscv/kvm/Makefile
>index 4e0bba91d284..06e2d52a9b88 100644
>--- a/arch/riscv/kvm/Makefile
>+++ b/arch/riscv/kvm/Makefile
>@@ -26,6 +26,7 @@ kvm-y += vcpu_onereg.o
> kvm-$(CONFIG_RISCV_PMU_SBI) += vcpu_pmu.o
> kvm-y += vcpu_sbi.o
> kvm-y += vcpu_sbi_base.o
>+kvm-y += vcpu_sbi_fwft.o
> kvm-y += vcpu_sbi_hsm.o
> kvm-$(CONFIG_RISCV_PMU_SBI) += vcpu_sbi_pmu.o
> kvm-y += vcpu_sbi_replace.o
>diff --git a/arch/riscv/kvm/vcpu_sbi.c b/arch/riscv/kvm/vcpu_sbi.c
>index f81f06f82650..3b37deaed4e7 100644
>--- a/arch/riscv/kvm/vcpu_sbi.c
>+++ b/arch/riscv/kvm/vcpu_sbi.c
>@@ -78,6 +78,10 @@ static const struct kvm_riscv_sbi_extension_entry sbi_ext[] = {
> 		.ext_idx = KVM_RISCV_SBI_EXT_STA,
> 		.ext_ptr = &vcpu_sbi_ext_sta,
> 	},
>+	{
>+		.ext_idx = KVM_RISCV_SBI_EXT_FWFT,
>+		.ext_ptr = &vcpu_sbi_ext_fwft,
>+	},
> 	{
> 		.ext_idx = KVM_RISCV_SBI_EXT_EXPERIMENTAL,
> 		.ext_ptr = &vcpu_sbi_ext_experimental,
>diff --git a/arch/riscv/kvm/vcpu_sbi_fwft.c b/arch/riscv/kvm/vcpu_sbi_fwft.c
>new file mode 100644
>index 000000000000..fe608bf16558
>--- /dev/null
>+++ b/arch/riscv/kvm/vcpu_sbi_fwft.c
>@@ -0,0 +1,187 @@
>+// SPDX-License-Identifier: GPL-2.0
>+/*
>+ * Copyright (c) 2025 Rivos Inc.
>+ *
>+ * Authors:
>+ *     Clément Léger <cleger@rivosinc.com>
>+ */
>+
>+#include <linux/errno.h>
>+#include <linux/err.h>
>+#include <linux/kvm_host.h>
>+#include <asm/cpufeature.h>
>+#include <asm/sbi.h>
>+#include <asm/kvm_vcpu_sbi.h>
>+#include <asm/kvm_vcpu_sbi_fwft.h>
>+
>+static const enum sbi_fwft_feature_t kvm_fwft_defined_features[] = {
>+	SBI_FWFT_MISALIGNED_EXC_DELEG,
>+	SBI_FWFT_LANDING_PAD,
>+	SBI_FWFT_SHADOW_STACK,
>+	SBI_FWFT_DOUBLE_TRAP,
>+	SBI_FWFT_PTE_AD_HW_UPDATING,
>+	SBI_FWFT_POINTER_MASKING_PMLEN,
>+};
>+
>+static bool kvm_fwft_is_defined_feature(enum sbi_fwft_feature_t feature)
>+{
>+	int i;
>+
>+	for (i = 0; i < ARRAY_SIZE(kvm_fwft_defined_features); i++) {
>+		if (kvm_fwft_defined_features[i] == feature)
>+			return true;
>+	}
>+
>+	return false;
>+}
>+
>+static const struct kvm_sbi_fwft_feature features[] = {
>+};
>+
>+static struct kvm_sbi_fwft_config *
>+kvm_sbi_fwft_get_config(struct kvm_vcpu *vcpu, enum sbi_fwft_feature_t feature)
>+{
>+	int i = 0;
>+	struct kvm_sbi_fwft *fwft = vcpu_to_fwft(vcpu);
>+
>+	for (i = 0; i < ARRAY_SIZE(features); i++) {
>+		if (fwft->configs[i].feature->id == feature)
>+			return &fwft->configs[i];
>+	}
>+
>+	return NULL;
>+}
>+
>+static int kvm_fwft_get_feature(struct kvm_vcpu *vcpu, unsigned long feature,
>+				struct kvm_sbi_fwft_config **conf)
>+{
>+	struct kvm_sbi_fwft_config *tconf;
>+
>+	/* Feature are defined as 32 bits identifiers */
>+	if (feature & ~(BIT_ULL(32) - 1))
>+		return SBI_ERR_INVALID_PARAM;
>+
>+	tconf = kvm_sbi_fwft_get_config(vcpu, feature);
>+	if (!tconf) {
>+		if (kvm_fwft_is_defined_feature(feature))
>+			return SBI_ERR_NOT_SUPPORTED;
>+
>+		return SBI_ERR_DENIED;
>+	}
>+
>+	if (!tconf->supported)
>+		return SBI_ERR_NOT_SUPPORTED;
>+
>+	*conf = tconf;
>+
>+	return SBI_SUCCESS;
>+}
>+
>+static int kvm_sbi_fwft_set(struct kvm_vcpu *vcpu, unsigned long feature,
>+			    unsigned long value, unsigned long flags)
>+{
>+	int ret;
>+	struct kvm_sbi_fwft_config *conf;
>+
>+	ret = kvm_fwft_get_feature(vcpu, feature, &conf);
>+	if (ret)
>+		return ret;
>+
>+	if ((flags & ~SBI_FWFT_SET_FLAG_LOCK) != 0)
>+		return SBI_ERR_INVALID_PARAM;
>+
>+	if (conf->flags & SBI_FWFT_SET_FLAG_LOCK)
>+		return SBI_ERR_DENIED_LOCKED;
>+
>+	conf->flags = flags;
>+
>+	return conf->feature->set(vcpu, conf, value);
>+}
>+
>+static int kvm_sbi_fwft_get(struct kvm_vcpu *vcpu, unsigned long feature,
>+			    unsigned long *value)
>+{
>+	int ret;
>+	struct kvm_sbi_fwft_config *conf;
>+
>+	ret = kvm_fwft_get_feature(vcpu, feature, &conf);
>+	if (ret)
>+		return ret;
>+
>+	return conf->feature->get(vcpu, conf, value);
>+}
>+
>+static int kvm_sbi_ext_fwft_handler(struct kvm_vcpu *vcpu, struct kvm_run *run,
>+				    struct kvm_vcpu_sbi_return *retdata)
>+{
>+	int ret = 0;
>+	struct kvm_cpu_context *cp = &vcpu->arch.guest_context;
>+	unsigned long funcid = cp->a6;
>+
>+	switch (funcid) {
>+	case SBI_EXT_FWFT_SET:
>+		ret = kvm_sbi_fwft_set(vcpu, cp->a0, cp->a1, cp->a2);
>+		break;
>+	case SBI_EXT_FWFT_GET:
>+		ret = kvm_sbi_fwft_get(vcpu, cp->a0, &retdata->out_val);
>+		break;
>+	default:
>+		ret = SBI_ERR_NOT_SUPPORTED;
>+		break;
>+	}
>+
>+	retdata->err_val = ret;
>+
>+	return 0;
>+}
>+
>+static int kvm_sbi_ext_fwft_init(struct kvm_vcpu *vcpu)
>+{
>+	struct kvm_sbi_fwft *fwft = vcpu_to_fwft(vcpu);
>+	const struct kvm_sbi_fwft_feature *feature;
>+	struct kvm_sbi_fwft_config *conf;
>+	int i;
>+
>+	fwft->configs = kcalloc(ARRAY_SIZE(features), sizeof(struct kvm_sbi_fwft_config),
>+				GFP_KERNEL);
>+	if (!fwft->configs)
>+		return -ENOMEM;
>+
>+	for (i = 0; i < ARRAY_SIZE(features); i++) {
>+		feature = &features[i];
>+		conf = &fwft->configs[i];
>+		if (feature->supported)
>+			conf->supported = feature->supported(vcpu);
>+		else
>+			conf->supported = true;
>+
>+		conf->feature = feature;
>+	}
>+
>+	return 0;
>+}
>+
>+static void kvm_sbi_ext_fwft_deinit(struct kvm_vcpu *vcpu)
>+{
>+	struct kvm_sbi_fwft *fwft = vcpu_to_fwft(vcpu);
>+
>+	kfree(fwft->configs);
>+}
>+
>+static void kvm_sbi_ext_fwft_reset(struct kvm_vcpu *vcpu)
>+{
>+	int i = 0;
>+	struct kvm_sbi_fwft *fwft = vcpu_to_fwft(vcpu);
>+
>+	for (i = 0; i < ARRAY_SIZE(features); i++)
>+		fwft->configs[i].flags = 0;
>+}
>+
>+const struct kvm_vcpu_sbi_extension vcpu_sbi_ext_fwft = {
>+	.extid_start = SBI_EXT_FWFT,
>+	.extid_end = SBI_EXT_FWFT,
>+	.handler = kvm_sbi_ext_fwft_handler,
>+	.init = kvm_sbi_ext_fwft_init,
>+	.deinit = kvm_sbi_ext_fwft_deinit,
>+	.reset = kvm_sbi_ext_fwft_reset,
>+};
>-- 
>2.47.2
>
>

On 11/02/2025 06:57, Deepak Gupta wrote:
> On Mon, Feb 10, 2025 at 10:35:47PM +0100, Clément Léger wrote:
>> Add basic infrastructure to support the FWFT extension in KVM.
>>
>> Signed-off-by: Clément Léger <cleger@rivosinc.com>
>> ---
>> arch/riscv/include/asm/kvm_host.h          |   4 +
>> arch/riscv/include/asm/kvm_vcpu_sbi.h      |   1 +
>> arch/riscv/include/asm/kvm_vcpu_sbi_fwft.h |  37 ++++
>> arch/riscv/include/uapi/asm/kvm.h          |   1 +
>> arch/riscv/kvm/Makefile                    |   1 +
>> arch/riscv/kvm/vcpu_sbi.c                  |   4 +
>> arch/riscv/kvm/vcpu_sbi_fwft.c             | 187 +++++++++++++++++++++
>> 7 files changed, 235 insertions(+)
>> create mode 100644 arch/riscv/include/asm/kvm_vcpu_sbi_fwft.h
>> create mode 100644 arch/riscv/kvm/vcpu_sbi_fwft.c
>>
>> diff --git a/arch/riscv/include/asm/kvm_host.h b/arch/riscv/include/
>> asm/kvm_host.h
>> index bb93d2995ea2..c0db61ba691a 100644
>> --- a/arch/riscv/include/asm/kvm_host.h
>> +++ b/arch/riscv/include/asm/kvm_host.h
>> @@ -19,6 +19,7 @@
>> #include <asm/kvm_vcpu_fp.h>
>> #include <asm/kvm_vcpu_insn.h>
>> #include <asm/kvm_vcpu_sbi.h>
>> +#include <asm/kvm_vcpu_sbi_fwft.h>
>> #include <asm/kvm_vcpu_timer.h>
>> #include <asm/kvm_vcpu_pmu.h>
>>
>> @@ -281,6 +282,9 @@ struct kvm_vcpu_arch {
>>     /* Performance monitoring context */
>>     struct kvm_pmu pmu_context;
>>
>> +    /* Firmware feature SBI extension context */
>> +    struct kvm_sbi_fwft fwft_context;
>> +
>>     /* 'static' configurations which are set only once */
>>     struct kvm_vcpu_config cfg;
>>
>> diff --git a/arch/riscv/include/asm/kvm_vcpu_sbi.h b/arch/riscv/
>> include/asm/kvm_vcpu_sbi.h
>> index cb68b3a57c8f..ffd03fed0c06 100644
>> --- a/arch/riscv/include/asm/kvm_vcpu_sbi.h
>> +++ b/arch/riscv/include/asm/kvm_vcpu_sbi.h
>> @@ -98,6 +98,7 @@ extern const struct kvm_vcpu_sbi_extension
>> vcpu_sbi_ext_hsm;
>> extern const struct kvm_vcpu_sbi_extension vcpu_sbi_ext_dbcn;
>> extern const struct kvm_vcpu_sbi_extension vcpu_sbi_ext_susp;
>> extern const struct kvm_vcpu_sbi_extension vcpu_sbi_ext_sta;
>> +extern const struct kvm_vcpu_sbi_extension vcpu_sbi_ext_fwft;
>> extern const struct kvm_vcpu_sbi_extension vcpu_sbi_ext_experimental;
>> extern const struct kvm_vcpu_sbi_extension vcpu_sbi_ext_vendor;
>>
>> diff --git a/arch/riscv/include/asm/kvm_vcpu_sbi_fwft.h b/arch/riscv/
>> include/asm/kvm_vcpu_sbi_fwft.h
>> new file mode 100644
>> index 000000000000..5782517f6e08
>> --- /dev/null
>> +++ b/arch/riscv/include/asm/kvm_vcpu_sbi_fwft.h
>> @@ -0,0 +1,37 @@
>> +/* SPDX-License-Identifier: GPL-2.0-only */
>> +/*
>> + * Copyright (c) 2025 Rivos Inc.
>> + *
>> + * Authors:
>> + *     Clément Léger <cleger@rivosinc.com>
>> + */
>> +
>> +#ifndef __KVM_VCPU_RISCV_FWFT_H
>> +#define __KVM_VCPU_RISCV_FWFT_H
>> +
>> +#include <asm/sbi.h>
>> +
>> +struct kvm_sbi_fwft_config;
>> +struct kvm_vcpu;
>> +
> 
> 
> Can we add some comments here for future fwft providers along below lines?
> 
> Reason being, patch defaults to `conf->supported = true` if `supported` fn
> pointer in `kvm_sbi_fwft_feature` was NULL. Although `kvm_sbi_fwft_set/get`
> does get/set fn pointers (it would happen even if `supported` fn pointer
> was NULL).

Yes sure, I'll add some kernel doc comments.

Thanks,

Clément

> 
>> +struct kvm_sbi_fwft_feature {
>> +    enum sbi_fwft_feature_t id;
>     /* If function not provided, KVM will default assume to be true */
>> +    bool (*supported)(struct kvm_vcpu *vcpu);
>     /* Must always provide function pointers for get/set */
>> +    int (*set)(struct kvm_vcpu *vcpu, struct kvm_sbi_fwft_config
>> *conf, unsigned long value);
>> +    int (*get)(struct kvm_vcpu *vcpu, struct kvm_sbi_fwft_config
>> *conf, unsigned long *value);
> 
> 
>> +};
>> +
>> +struct kvm_sbi_fwft_config {
>> +    const struct kvm_sbi_fwft_feature *feature;
>> +    bool supported;
>> +    unsigned long flags;
>> +};
>> +
>> +/* FWFT data structure per vcpu */
>> +struct kvm_sbi_fwft {
>> +    struct kvm_sbi_fwft_config *configs;
>> +};
>> +
>> +#define vcpu_to_fwft(vcpu) (&(vcpu)->arch.fwft_context)
>> +
>> +#endif /* !__KVM_VCPU_RISCV_FWFT_H */
>> diff --git a/arch/riscv/include/uapi/asm/kvm.h b/arch/riscv/include/
>> uapi/asm/kvm.h
>> index f06bc5efcd79..fa6eee1caf41 100644
>> --- a/arch/riscv/include/uapi/asm/kvm.h
>> +++ b/arch/riscv/include/uapi/asm/kvm.h
>> @@ -202,6 +202,7 @@ enum KVM_RISCV_SBI_EXT_ID {
>>     KVM_RISCV_SBI_EXT_DBCN,
>>     KVM_RISCV_SBI_EXT_STA,
>>     KVM_RISCV_SBI_EXT_SUSP,
>> +    KVM_RISCV_SBI_EXT_FWFT,
>>     KVM_RISCV_SBI_EXT_MAX,
>> };
>>
>> diff --git a/arch/riscv/kvm/Makefile b/arch/riscv/kvm/Makefile
>> index 4e0bba91d284..06e2d52a9b88 100644
>> --- a/arch/riscv/kvm/Makefile
>> +++ b/arch/riscv/kvm/Makefile
>> @@ -26,6 +26,7 @@ kvm-y += vcpu_onereg.o
>> kvm-$(CONFIG_RISCV_PMU_SBI) += vcpu_pmu.o
>> kvm-y += vcpu_sbi.o
>> kvm-y += vcpu_sbi_base.o
>> +kvm-y += vcpu_sbi_fwft.o
>> kvm-y += vcpu_sbi_hsm.o
>> kvm-$(CONFIG_RISCV_PMU_SBI) += vcpu_sbi_pmu.o
>> kvm-y += vcpu_sbi_replace.o
>> diff --git a/arch/riscv/kvm/vcpu_sbi.c b/arch/riscv/kvm/vcpu_sbi.c
>> index f81f06f82650..3b37deaed4e7 100644
>> --- a/arch/riscv/kvm/vcpu_sbi.c
>> +++ b/arch/riscv/kvm/vcpu_sbi.c
>> @@ -78,6 +78,10 @@ static const struct kvm_riscv_sbi_extension_entry
>> sbi_ext[] = {
>>         .ext_idx = KVM_RISCV_SBI_EXT_STA,
>>         .ext_ptr = &vcpu_sbi_ext_sta,
>>     },
>> +    {
>> +        .ext_idx = KVM_RISCV_SBI_EXT_FWFT,
>> +        .ext_ptr = &vcpu_sbi_ext_fwft,
>> +    },
>>     {
>>         .ext_idx = KVM_RISCV_SBI_EXT_EXPERIMENTAL,
>>         .ext_ptr = &vcpu_sbi_ext_experimental,
>> diff --git a/arch/riscv/kvm/vcpu_sbi_fwft.c b/arch/riscv/kvm/
>> vcpu_sbi_fwft.c
>> new file mode 100644
>> index 000000000000..fe608bf16558
>> --- /dev/null
>> +++ b/arch/riscv/kvm/vcpu_sbi_fwft.c
>> @@ -0,0 +1,187 @@
>> +// SPDX-License-Identifier: GPL-2.0
>> +/*
>> + * Copyright (c) 2025 Rivos Inc.
>> + *
>> + * Authors:
>> + *     Clément Léger <cleger@rivosinc.com>
>> + */
>> +
>> +#include <linux/errno.h>
>> +#include <linux/err.h>
>> +#include <linux/kvm_host.h>
>> +#include <asm/cpufeature.h>
>> +#include <asm/sbi.h>
>> +#include <asm/kvm_vcpu_sbi.h>
>> +#include <asm/kvm_vcpu_sbi_fwft.h>
>> +
>> +static const enum sbi_fwft_feature_t kvm_fwft_defined_features[] = {
>> +    SBI_FWFT_MISALIGNED_EXC_DELEG,
>> +    SBI_FWFT_LANDING_PAD,
>> +    SBI_FWFT_SHADOW_STACK,
>> +    SBI_FWFT_DOUBLE_TRAP,
>> +    SBI_FWFT_PTE_AD_HW_UPDATING,
>> +    SBI_FWFT_POINTER_MASKING_PMLEN,
>> +};
>> +
>> +static bool kvm_fwft_is_defined_feature(enum sbi_fwft_feature_t feature)
>> +{
>> +    int i;
>> +
>> +    for (i = 0; i < ARRAY_SIZE(kvm_fwft_defined_features); i++) {
>> +        if (kvm_fwft_defined_features[i] == feature)
>> +            return true;
>> +    }
>> +
>> +    return false;
>> +}
>> +
>> +static const struct kvm_sbi_fwft_feature features[] = {
>> +};
>> +
>> +static struct kvm_sbi_fwft_config *
>> +kvm_sbi_fwft_get_config(struct kvm_vcpu *vcpu, enum
>> sbi_fwft_feature_t feature)
>> +{
>> +    int i = 0;
>> +    struct kvm_sbi_fwft *fwft = vcpu_to_fwft(vcpu);
>> +
>> +    for (i = 0; i < ARRAY_SIZE(features); i++) {
>> +        if (fwft->configs[i].feature->id == feature)
>> +            return &fwft->configs[i];
>> +    }
>> +
>> +    return NULL;
>> +}
>> +
>> +static int kvm_fwft_get_feature(struct kvm_vcpu *vcpu, unsigned long
>> feature,
>> +                struct kvm_sbi_fwft_config **conf)
>> +{
>> +    struct kvm_sbi_fwft_config *tconf;
>> +
>> +    /* Feature are defined as 32 bits identifiers */
>> +    if (feature & ~(BIT_ULL(32) - 1))
>> +        return SBI_ERR_INVALID_PARAM;
>> +
>> +    tconf = kvm_sbi_fwft_get_config(vcpu, feature);
>> +    if (!tconf) {
>> +        if (kvm_fwft_is_defined_feature(feature))
>> +            return SBI_ERR_NOT_SUPPORTED;
>> +
>> +        return SBI_ERR_DENIED;
>> +    }
>> +
>> +    if (!tconf->supported)
>> +        return SBI_ERR_NOT_SUPPORTED;
>> +
>> +    *conf = tconf;
>> +
>> +    return SBI_SUCCESS;
>> +}
>> +
>> +static int kvm_sbi_fwft_set(struct kvm_vcpu *vcpu, unsigned long
>> feature,
>> +                unsigned long value, unsigned long flags)
>> +{
>> +    int ret;
>> +    struct kvm_sbi_fwft_config *conf;
>> +
>> +    ret = kvm_fwft_get_feature(vcpu, feature, &conf);
>> +    if (ret)
>> +        return ret;
>> +
>> +    if ((flags & ~SBI_FWFT_SET_FLAG_LOCK) != 0)
>> +        return SBI_ERR_INVALID_PARAM;
>> +
>> +    if (conf->flags & SBI_FWFT_SET_FLAG_LOCK)
>> +        return SBI_ERR_DENIED_LOCKED;
>> +
>> +    conf->flags = flags;
>> +
>> +    return conf->feature->set(vcpu, conf, value);
>> +}
>> +
>> +static int kvm_sbi_fwft_get(struct kvm_vcpu *vcpu, unsigned long
>> feature,
>> +                unsigned long *value)
>> +{
>> +    int ret;
>> +    struct kvm_sbi_fwft_config *conf;
>> +
>> +    ret = kvm_fwft_get_feature(vcpu, feature, &conf);
>> +    if (ret)
>> +        return ret;
>> +
>> +    return conf->feature->get(vcpu, conf, value);
>> +}
>> +
>> +static int kvm_sbi_ext_fwft_handler(struct kvm_vcpu *vcpu, struct
>> kvm_run *run,
>> +                    struct kvm_vcpu_sbi_return *retdata)
>> +{
>> +    int ret = 0;
>> +    struct kvm_cpu_context *cp = &vcpu->arch.guest_context;
>> +    unsigned long funcid = cp->a6;
>> +
>> +    switch (funcid) {
>> +    case SBI_EXT_FWFT_SET:
>> +        ret = kvm_sbi_fwft_set(vcpu, cp->a0, cp->a1, cp->a2);
>> +        break;
>> +    case SBI_EXT_FWFT_GET:
>> +        ret = kvm_sbi_fwft_get(vcpu, cp->a0, &retdata->out_val);
>> +        break;
>> +    default:
>> +        ret = SBI_ERR_NOT_SUPPORTED;
>> +        break;
>> +    }
>> +
>> +    retdata->err_val = ret;
>> +
>> +    return 0;
>> +}
>> +
>> +static int kvm_sbi_ext_fwft_init(struct kvm_vcpu *vcpu)
>> +{
>> +    struct kvm_sbi_fwft *fwft = vcpu_to_fwft(vcpu);
>> +    const struct kvm_sbi_fwft_feature *feature;
>> +    struct kvm_sbi_fwft_config *conf;
>> +    int i;
>> +
>> +    fwft->configs = kcalloc(ARRAY_SIZE(features), sizeof(struct
>> kvm_sbi_fwft_config),
>> +                GFP_KERNEL);
>> +    if (!fwft->configs)
>> +        return -ENOMEM;
>> +
>> +    for (i = 0; i < ARRAY_SIZE(features); i++) {
>> +        feature = &features[i];
>> +        conf = &fwft->configs[i];
>> +        if (feature->supported)
>> +            conf->supported = feature->supported(vcpu);
>> +        else
>> +            conf->supported = true;
>> +
>> +        conf->feature = feature;
>> +    }
>> +
>> +    return 0;
>> +}
>> +
>> +static void kvm_sbi_ext_fwft_deinit(struct kvm_vcpu *vcpu)
>> +{
>> +    struct kvm_sbi_fwft *fwft = vcpu_to_fwft(vcpu);
>> +
>> +    kfree(fwft->configs);
>> +}
>> +
>> +static void kvm_sbi_ext_fwft_reset(struct kvm_vcpu *vcpu)
>> +{
>> +    int i = 0;
>> +    struct kvm_sbi_fwft *fwft = vcpu_to_fwft(vcpu);
>> +
>> +    for (i = 0; i < ARRAY_SIZE(features); i++)
>> +        fwft->configs[i].flags = 0;
>> +}
>> +
>> +const struct kvm_vcpu_sbi_extension vcpu_sbi_ext_fwft = {
>> +    .extid_start = SBI_EXT_FWFT,
>> +    .extid_end = SBI_EXT_FWFT,
>> +    .handler = kvm_sbi_ext_fwft_handler,
>> +    .init = kvm_sbi_ext_fwft_init,
>> +    .deinit = kvm_sbi_ext_fwft_deinit,
>> +    .reset = kvm_sbi_ext_fwft_reset,
>> +};
>> -- 
>> 2.47.2
>>
>>

On Mon, Feb 10, 2025 at 10:35:47PM +0100, Clément Léger wrote:
>Add basic infrastructure to support the FWFT extension in KVM.
>
>Signed-off-by: Clément Léger <cleger@rivosinc.com>
>---
> arch/riscv/include/asm/kvm_host.h          |   4 +
> arch/riscv/include/asm/kvm_vcpu_sbi.h      |   1 +
> arch/riscv/include/asm/kvm_vcpu_sbi_fwft.h |  37 ++++
> arch/riscv/include/uapi/asm/kvm.h          |   1 +
> arch/riscv/kvm/Makefile                    |   1 +
> arch/riscv/kvm/vcpu_sbi.c                  |   4 +
> arch/riscv/kvm/vcpu_sbi_fwft.c             | 187 +++++++++++++++++++++
> 7 files changed, 235 insertions(+)
> create mode 100644 arch/riscv/include/asm/kvm_vcpu_sbi_fwft.h
> create mode 100644 arch/riscv/kvm/vcpu_sbi_fwft.c
>
>diff --git a/arch/riscv/include/asm/kvm_host.h b/arch/riscv/include/asm/kvm_host.h
>index bb93d2995ea2..c0db61ba691a 100644
>--- a/arch/riscv/include/asm/kvm_host.h
>+++ b/arch/riscv/include/asm/kvm_host.h
>@@ -19,6 +19,7 @@
> #include <asm/kvm_vcpu_fp.h>
> #include <asm/kvm_vcpu_insn.h>
> #include <asm/kvm_vcpu_sbi.h>
>+#include <asm/kvm_vcpu_sbi_fwft.h>
> #include <asm/kvm_vcpu_timer.h>
> #include <asm/kvm_vcpu_pmu.h>
>
>@@ -281,6 +282,9 @@ struct kvm_vcpu_arch {
> 	/* Performance monitoring context */
> 	struct kvm_pmu pmu_context;
>
>+	/* Firmware feature SBI extension context */
>+	struct kvm_sbi_fwft fwft_context;
>+
> 	/* 'static' configurations which are set only once */
> 	struct kvm_vcpu_config cfg;
>
>diff --git a/arch/riscv/include/asm/kvm_vcpu_sbi.h b/arch/riscv/include/asm/kvm_vcpu_sbi.h
>index cb68b3a57c8f..ffd03fed0c06 100644
>--- a/arch/riscv/include/asm/kvm_vcpu_sbi.h
>+++ b/arch/riscv/include/asm/kvm_vcpu_sbi.h
>@@ -98,6 +98,7 @@ extern const struct kvm_vcpu_sbi_extension vcpu_sbi_ext_hsm;
> extern const struct kvm_vcpu_sbi_extension vcpu_sbi_ext_dbcn;
> extern const struct kvm_vcpu_sbi_extension vcpu_sbi_ext_susp;
> extern const struct kvm_vcpu_sbi_extension vcpu_sbi_ext_sta;
>+extern const struct kvm_vcpu_sbi_extension vcpu_sbi_ext_fwft;
> extern const struct kvm_vcpu_sbi_extension vcpu_sbi_ext_experimental;
> extern const struct kvm_vcpu_sbi_extension vcpu_sbi_ext_vendor;
>
>diff --git a/arch/riscv/include/asm/kvm_vcpu_sbi_fwft.h b/arch/riscv/include/asm/kvm_vcpu_sbi_fwft.h
>new file mode 100644
>index 000000000000..5782517f6e08
>--- /dev/null
>+++ b/arch/riscv/include/asm/kvm_vcpu_sbi_fwft.h
>@@ -0,0 +1,37 @@
>+/* SPDX-License-Identifier: GPL-2.0-only */
>+/*
>+ * Copyright (c) 2025 Rivos Inc.
>+ *
>+ * Authors:
>+ *     Clément Léger <cleger@rivosinc.com>
>+ */
>+
>+#ifndef __KVM_VCPU_RISCV_FWFT_H
>+#define __KVM_VCPU_RISCV_FWFT_H
>+
>+#include <asm/sbi.h>
>+
>+struct kvm_sbi_fwft_config;
>+struct kvm_vcpu;
>+
>+struct kvm_sbi_fwft_feature {
>+	enum sbi_fwft_feature_t id;
>+	bool (*supported)(struct kvm_vcpu *vcpu);
>+	int (*set)(struct kvm_vcpu *vcpu, struct kvm_sbi_fwft_config *conf, unsigned long value);
>+	int (*get)(struct kvm_vcpu *vcpu, struct kvm_sbi_fwft_config *conf, unsigned long *value);
>+};
>+
>+struct kvm_sbi_fwft_config {
>+	const struct kvm_sbi_fwft_feature *feature;
>+	bool supported;
>+	unsigned long flags;
>+};
>+
>+/* FWFT data structure per vcpu */
>+struct kvm_sbi_fwft {
>+	struct kvm_sbi_fwft_config *configs;
>+};
>+
>+#define vcpu_to_fwft(vcpu) (&(vcpu)->arch.fwft_context)
>+
>+#endif /* !__KVM_VCPU_RISCV_FWFT_H */
>diff --git a/arch/riscv/include/uapi/asm/kvm.h b/arch/riscv/include/uapi/asm/kvm.h
>index f06bc5efcd79..fa6eee1caf41 100644
>--- a/arch/riscv/include/uapi/asm/kvm.h
>+++ b/arch/riscv/include/uapi/asm/kvm.h
>@@ -202,6 +202,7 @@ enum KVM_RISCV_SBI_EXT_ID {
> 	KVM_RISCV_SBI_EXT_DBCN,
> 	KVM_RISCV_SBI_EXT_STA,
> 	KVM_RISCV_SBI_EXT_SUSP,
>+	KVM_RISCV_SBI_EXT_FWFT,
> 	KVM_RISCV_SBI_EXT_MAX,
> };
>
>diff --git a/arch/riscv/kvm/Makefile b/arch/riscv/kvm/Makefile
>index 4e0bba91d284..06e2d52a9b88 100644
>--- a/arch/riscv/kvm/Makefile
>+++ b/arch/riscv/kvm/Makefile
>@@ -26,6 +26,7 @@ kvm-y += vcpu_onereg.o
> kvm-$(CONFIG_RISCV_PMU_SBI) += vcpu_pmu.o
> kvm-y += vcpu_sbi.o
> kvm-y += vcpu_sbi_base.o
>+kvm-y += vcpu_sbi_fwft.o
> kvm-y += vcpu_sbi_hsm.o
> kvm-$(CONFIG_RISCV_PMU_SBI) += vcpu_sbi_pmu.o
> kvm-y += vcpu_sbi_replace.o
>diff --git a/arch/riscv/kvm/vcpu_sbi.c b/arch/riscv/kvm/vcpu_sbi.c
>index f81f06f82650..3b37deaed4e7 100644
>--- a/arch/riscv/kvm/vcpu_sbi.c
>+++ b/arch/riscv/kvm/vcpu_sbi.c
>@@ -78,6 +78,10 @@ static const struct kvm_riscv_sbi_extension_entry sbi_ext[] = {
> 		.ext_idx = KVM_RISCV_SBI_EXT_STA,
> 		.ext_ptr = &vcpu_sbi_ext_sta,
> 	},
>+	{
>+		.ext_idx = KVM_RISCV_SBI_EXT_FWFT,
>+		.ext_ptr = &vcpu_sbi_ext_fwft,
>+	},
> 	{
> 		.ext_idx = KVM_RISCV_SBI_EXT_EXPERIMENTAL,
> 		.ext_ptr = &vcpu_sbi_ext_experimental,
>diff --git a/arch/riscv/kvm/vcpu_sbi_fwft.c b/arch/riscv/kvm/vcpu_sbi_fwft.c
>new file mode 100644
>index 000000000000..fe608bf16558
>--- /dev/null
>+++ b/arch/riscv/kvm/vcpu_sbi_fwft.c
>@@ -0,0 +1,187 @@
>+// SPDX-License-Identifier: GPL-2.0
>+/*
>+ * Copyright (c) 2025 Rivos Inc.
>+ *
>+ * Authors:
>+ *     Clément Léger <cleger@rivosinc.com>
>+ */
>+
>+#include <linux/errno.h>
>+#include <linux/err.h>
>+#include <linux/kvm_host.h>
>+#include <asm/cpufeature.h>
>+#include <asm/sbi.h>
>+#include <asm/kvm_vcpu_sbi.h>
>+#include <asm/kvm_vcpu_sbi_fwft.h>
>+
>+static const enum sbi_fwft_feature_t kvm_fwft_defined_features[] = {
>+	SBI_FWFT_MISALIGNED_EXC_DELEG,
>+	SBI_FWFT_LANDING_PAD,
>+	SBI_FWFT_SHADOW_STACK,
>+	SBI_FWFT_DOUBLE_TRAP,
>+	SBI_FWFT_PTE_AD_HW_UPDATING,
>+	SBI_FWFT_POINTER_MASKING_PMLEN,
>+};
>+
>+static bool kvm_fwft_is_defined_feature(enum sbi_fwft_feature_t feature)
>+{
>+	int i;
>+
>+	for (i = 0; i < ARRAY_SIZE(kvm_fwft_defined_features); i++) {
>+		if (kvm_fwft_defined_features[i] == feature)
>+			return true;
>+	}
>+
>+	return false;
>+}
>+
>+static const struct kvm_sbi_fwft_feature features[] = {
>+};
>+
>+static struct kvm_sbi_fwft_config *
>+kvm_sbi_fwft_get_config(struct kvm_vcpu *vcpu, enum sbi_fwft_feature_t feature)
>+{
>+	int i = 0;
>+	struct kvm_sbi_fwft *fwft = vcpu_to_fwft(vcpu);
>+
>+	for (i = 0; i < ARRAY_SIZE(features); i++) {
>+		if (fwft->configs[i].feature->id == feature)
>+			return &fwft->configs[i];
>+	}
>+
>+	return NULL;
>+}
>+
>+static int kvm_fwft_get_feature(struct kvm_vcpu *vcpu, unsigned long feature,
>+				struct kvm_sbi_fwft_config **conf)
>+{
>+	struct kvm_sbi_fwft_config *tconf;
>+
>+	/* Feature are defined as 32 bits identifiers */
>+	if (feature & ~(BIT_ULL(32) - 1))
>+		return SBI_ERR_INVALID_PARAM;
>+
>+	tconf = kvm_sbi_fwft_get_config(vcpu, feature);
>+	if (!tconf) {
>+		if (kvm_fwft_is_defined_feature(feature))
>+			return SBI_ERR_NOT_SUPPORTED;
>+
>+		return SBI_ERR_DENIED;
>+	}
>+
>+	if (!tconf->supported)
>+		return SBI_ERR_NOT_SUPPORTED;
>+
>+	*conf = tconf;
>+
>+	return SBI_SUCCESS;
>+}
>+
>+static int kvm_sbi_fwft_set(struct kvm_vcpu *vcpu, unsigned long feature,
>+			    unsigned long value, unsigned long flags)
>+{
>+	int ret;
>+	struct kvm_sbi_fwft_config *conf;
>+
>+	ret = kvm_fwft_get_feature(vcpu, feature, &conf);
>+	if (ret)
>+		return ret;
>+
>+	if ((flags & ~SBI_FWFT_SET_FLAG_LOCK) != 0)
>+		return SBI_ERR_INVALID_PARAM;
>+
>+	if (conf->flags & SBI_FWFT_SET_FLAG_LOCK)
>+		return SBI_ERR_DENIED_LOCKED;
>+
>+	conf->flags = flags;
>+
>+	return conf->feature->set(vcpu, conf, value);
>+}
>+
>+static int kvm_sbi_fwft_get(struct kvm_vcpu *vcpu, unsigned long feature,
>+			    unsigned long *value)
>+{
>+	int ret;
>+	struct kvm_sbi_fwft_config *conf;
>+
>+	ret = kvm_fwft_get_feature(vcpu, feature, &conf);
>+	if (ret)
>+		return ret;
>+
>+	return conf->feature->get(vcpu, conf, value);
>+}
>+
>+static int kvm_sbi_ext_fwft_handler(struct kvm_vcpu *vcpu, struct kvm_run *run,
>+				    struct kvm_vcpu_sbi_return *retdata)
>+{
>+	int ret = 0;
>+	struct kvm_cpu_context *cp = &vcpu->arch.guest_context;
>+	unsigned long funcid = cp->a6;
>+
>+	switch (funcid) {
>+	case SBI_EXT_FWFT_SET:
>+		ret = kvm_sbi_fwft_set(vcpu, cp->a0, cp->a1, cp->a2);
>+		break;
>+	case SBI_EXT_FWFT_GET:
>+		ret = kvm_sbi_fwft_get(vcpu, cp->a0, &retdata->out_val);
>+		break;
>+	default:
>+		ret = SBI_ERR_NOT_SUPPORTED;
>+		break;
>+	}
>+
>+	retdata->err_val = ret;
>+
>+	return 0;
>+}
>+
>+static int kvm_sbi_ext_fwft_init(struct kvm_vcpu *vcpu)
>+{
>+	struct kvm_sbi_fwft *fwft = vcpu_to_fwft(vcpu);
>+	const struct kvm_sbi_fwft_feature *feature;
>+	struct kvm_sbi_fwft_config *conf;
>+	int i;
>+
>+	fwft->configs = kcalloc(ARRAY_SIZE(features), sizeof(struct kvm_sbi_fwft_config),
>+				GFP_KERNEL);
nit:

I understand that in next patch you grow the static array`features`. But in this patch
`ARRAY_SIZE(features)` evaluates to 0, thus kcalloc will be returning a pointer
to some slab block (IIRC, kcalloc will not return NULL if size eventually evals to 0)

This probably won't result in some bad stuff. But still there is a pointer in
fwft->configs which is pointing to some random stuff if `features` turns out to be
empty.

Let me know if I got that right or missing something.

>+	if (!fwft->configs)
>+		return -ENOMEM;
>+
>+	for (i = 0; i < ARRAY_SIZE(features); i++) {
>+		feature = &features[i];
>+		conf = &fwft->configs[i];
>+		if (feature->supported)
>+			conf->supported = feature->supported(vcpu);
>+		else
>+			conf->supported = true;
>+
>+		conf->feature = feature;
>+	}
>+
>+	return 0;
>+}
>+
>+static void kvm_sbi_ext_fwft_deinit(struct kvm_vcpu *vcpu)
>+{
>+	struct kvm_sbi_fwft *fwft = vcpu_to_fwft(vcpu);
>+
>+	kfree(fwft->configs);
>+}
>+
>+static void kvm_sbi_ext_fwft_reset(struct kvm_vcpu *vcpu)
>+{
>+	int i = 0;
>+	struct kvm_sbi_fwft *fwft = vcpu_to_fwft(vcpu);
>+
>+	for (i = 0; i < ARRAY_SIZE(features); i++)
>+		fwft->configs[i].flags = 0;
>+}
>+
>+const struct kvm_vcpu_sbi_extension vcpu_sbi_ext_fwft = {
>+	.extid_start = SBI_EXT_FWFT,
>+	.extid_end = SBI_EXT_FWFT,
>+	.handler = kvm_sbi_ext_fwft_handler,
>+	.init = kvm_sbi_ext_fwft_init,
>+	.deinit = kvm_sbi_ext_fwft_deinit,
>+	.reset = kvm_sbi_ext_fwft_reset,
>+};
>-- 
>2.47.2
>
>

On 11/02/2025 06:43, Deepak Gupta wrote:
>> +static int kvm_sbi_fwft_get(struct kvm_vcpu *vcpu, unsigned long
>> feature,
>> +                unsigned long *value)
>> +{
>> +    int ret;
>> +    struct kvm_sbi_fwft_config *conf;
>> +
>> +    ret = kvm_fwft_get_feature(vcpu, feature, &conf);
>> +    if (ret)
>> +        return ret;
>> +
>> +    return conf->feature->get(vcpu, conf, value);
>> +}
>> +
>> +static int kvm_sbi_ext_fwft_handler(struct kvm_vcpu *vcpu, struct
>> kvm_run *run,
>> +                    struct kvm_vcpu_sbi_return *retdata)
>> +{
>> +    int ret = 0;
>> +    struct kvm_cpu_context *cp = &vcpu->arch.guest_context;
>> +    unsigned long funcid = cp->a6;
>> +
>> +    switch (funcid) {
>> +    case SBI_EXT_FWFT_SET:
>> +        ret = kvm_sbi_fwft_set(vcpu, cp->a0, cp->a1, cp->a2);
>> +        break;
>> +    case SBI_EXT_FWFT_GET:
>> +        ret = kvm_sbi_fwft_get(vcpu, cp->a0, &retdata->out_val);
>> +        break;
>> +    default:
>> +        ret = SBI_ERR_NOT_SUPPORTED;
>> +        break;
>> +    }
>> +
>> +    retdata->err_val = ret;
>> +
>> +    return 0;
>> +}
>> +
>> +static int kvm_sbi_ext_fwft_init(struct kvm_vcpu *vcpu)
>> +{
>> +    struct kvm_sbi_fwft *fwft = vcpu_to_fwft(vcpu);
>> +    const struct kvm_sbi_fwft_feature *feature;
>> +    struct kvm_sbi_fwft_config *conf;
>> +    int i;
>> +
>> +    fwft->configs = kcalloc(ARRAY_SIZE(features), sizeof(struct
>> kvm_sbi_fwft_config),
>> +                GFP_KERNEL);
> nit:
> 
> I understand that in next patch you grow the static array`features`. But
> in this patch
> `ARRAY_SIZE(features)` evaluates to 0, thus kcalloc will be returning a
> pointer
> to some slab block (IIRC, kcalloc will not return NULL if size
> eventually evals to 0)
> 
> This probably won't result in some bad stuff. But still there is a
> pointer in
> fwft->configs which is pointing to some random stuff if `features` turns
> out to be
> empty.
> 
> Let me know if I got that right or missing something.

So I actually searched into the kmalloc code to see what hapopens with a
zero size allocation and it actually return ZERO_SIZE_PTR:

/*
 * ZERO_SIZE_PTR will be returned for zero sized kmalloc requests.
 *
 * Dereferencing ZERO_SIZE_PTR will lead to a distinct access fault.
 *
 * ZERO_SIZE_PTR can be passed to kfree though in the same way that NULL
can.
 * Both make kfree a no-op.
 */

Which seems like it's not really random and will fault if accessed. I
think that's enough for that commit (which will be bisectable if needed
then).

Clément

On Tue, Feb 11, 2025 at 11:31:28AM +0100, Clément Léger wrote:
>
>
>On 11/02/2025 06:43, Deepak Gupta wrote:
>>> +static int kvm_sbi_fwft_get(struct kvm_vcpu *vcpu, unsigned long
>>> feature,
>>> +                unsigned long *value)
>>> +{
>>> +    int ret;
>>> +    struct kvm_sbi_fwft_config *conf;
>>> +
>>> +    ret = kvm_fwft_get_feature(vcpu, feature, &conf);
>>> +    if (ret)
>>> +        return ret;
>>> +
>>> +    return conf->feature->get(vcpu, conf, value);
>>> +}
>>> +
>>> +static int kvm_sbi_ext_fwft_handler(struct kvm_vcpu *vcpu, struct
>>> kvm_run *run,
>>> +                    struct kvm_vcpu_sbi_return *retdata)
>>> +{
>>> +    int ret = 0;
>>> +    struct kvm_cpu_context *cp = &vcpu->arch.guest_context;
>>> +    unsigned long funcid = cp->a6;
>>> +
>>> +    switch (funcid) {
>>> +    case SBI_EXT_FWFT_SET:
>>> +        ret = kvm_sbi_fwft_set(vcpu, cp->a0, cp->a1, cp->a2);
>>> +        break;
>>> +    case SBI_EXT_FWFT_GET:
>>> +        ret = kvm_sbi_fwft_get(vcpu, cp->a0, &retdata->out_val);
>>> +        break;
>>> +    default:
>>> +        ret = SBI_ERR_NOT_SUPPORTED;
>>> +        break;
>>> +    }
>>> +
>>> +    retdata->err_val = ret;
>>> +
>>> +    return 0;
>>> +}
>>> +
>>> +static int kvm_sbi_ext_fwft_init(struct kvm_vcpu *vcpu)
>>> +{
>>> +    struct kvm_sbi_fwft *fwft = vcpu_to_fwft(vcpu);
>>> +    const struct kvm_sbi_fwft_feature *feature;
>>> +    struct kvm_sbi_fwft_config *conf;
>>> +    int i;
>>> +
>>> +    fwft->configs = kcalloc(ARRAY_SIZE(features), sizeof(struct
>>> kvm_sbi_fwft_config),
>>> +                GFP_KERNEL);
>> nit:
>>
>> I understand that in next patch you grow the static array`features`. But
>> in this patch
>> `ARRAY_SIZE(features)` evaluates to 0, thus kcalloc will be returning a
>> pointer
>> to some slab block (IIRC, kcalloc will not return NULL if size
>> eventually evals to 0)
>>
>> This probably won't result in some bad stuff. But still there is a
>> pointer in
>> fwft->configs which is pointing to some random stuff if `features` turns
>> out to be
>> empty.
>>
>> Let me know if I got that right or missing something.
>
>So I actually searched into the kmalloc code to see what hapopens with a
>zero size allocation and it actually return ZERO_SIZE_PTR:
>
>/*
> * ZERO_SIZE_PTR will be returned for zero sized kmalloc requests.
> *
> * Dereferencing ZERO_SIZE_PTR will lead to a distinct access fault.
> *
> * ZERO_SIZE_PTR can be passed to kfree though in the same way that NULL
>can.
> * Both make kfree a no-op.
> */
>
>Which seems like it's not really random and will fault if accessed. I
>think that's enough for that commit (which will be bisectable if needed
>then).
>

Awesome. Thanks for looking into it.

>Clément