Add basic infrastructure to support the FWFT extension in KVM.

Signed-off-by: Clément Léger <cleger@rivosinc.com>
Reviewed-by: Andrew Jones <ajones@ventanamicro.com>
Reviewed-by: Atish Patra <atishp@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 |  29 +++
 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             | 216 +++++++++++++++++++++
 7 files changed, 256 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 4fa02e082142..c3f880763b9a 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..9ba841355758
--- /dev/null
+++ b/arch/riscv/include/asm/kvm_vcpu_sbi_fwft.h
@@ -0,0 +1,29 @@
+/* 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_feature;
+
+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 5f59fd226cc5..5ba77a3d9f6e 100644
--- a/arch/riscv/include/uapi/asm/kvm.h
+++ b/arch/riscv/include/uapi/asm/kvm.h
@@ -204,6 +204,7 @@ 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 50be079b5528..0748810c0252 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..b0f66c7bf010
--- /dev/null
+++ b/arch/riscv/kvm/vcpu_sbi_fwft.c
@@ -0,0 +1,216 @@
+// 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>
+
+struct kvm_sbi_fwft_feature {
+	/**
+	 * @id: Feature ID
+	 */
+	enum sbi_fwft_feature_t id;
+
+	/**
+	 * @supported: Check if the feature is supported on the vcpu
+	 *
+	 * This callback is optional, if not provided the feature is assumed to
+	 * be supported
+	 */
+	bool (*supported)(struct kvm_vcpu *vcpu);
+
+	/**
+	 * @set: Set the feature value
+	 *
+	 * Return SBI_SUCCESS on success or an SBI error (SBI_ERR_*)
+	 *
+	 * This callback is mandatory
+	 */
+	long (*set)(struct kvm_vcpu *vcpu, struct kvm_sbi_fwft_config *conf, unsigned long value);
+
+	/**
+	 * @get: Get the feature current value
+	 *
+	 * Return SBI_SUCCESS on success or an SBI error (SBI_ERR_*)
+	 *
+	 * This callback is mandatory
+	 */
+	long (*get)(struct kvm_vcpu *vcpu, struct kvm_sbi_fwft_config *conf, unsigned long *value);
+};
+
+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;
+	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, u32 feature,
+				struct kvm_sbi_fwft_config **conf)
+{
+	struct kvm_sbi_fwft_config *tconf;
+
+	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, u32 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;
+	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;
+	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,
+};
-- 
2.49.0

On Fri, May 23, 2025 at 3:52 PM Clément Léger <cleger@rivosinc.com> wrote:
>
> Add basic infrastructure to support the FWFT extension in KVM.
>
> Signed-off-by: Clément Léger <cleger@rivosinc.com>
> Reviewed-by: Andrew Jones <ajones@ventanamicro.com>
> Reviewed-by: Atish Patra <atishp@rivosinc.com>

Queued this patch for Linux-6.17

Thanks,
Anup

> ---
>  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 |  29 +++
>  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             | 216 +++++++++++++++++++++
>  7 files changed, 256 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 4fa02e082142..c3f880763b9a 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..9ba841355758
> --- /dev/null
> +++ b/arch/riscv/include/asm/kvm_vcpu_sbi_fwft.h
> @@ -0,0 +1,29 @@
> +/* 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_feature;
> +
> +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 5f59fd226cc5..5ba77a3d9f6e 100644
> --- a/arch/riscv/include/uapi/asm/kvm.h
> +++ b/arch/riscv/include/uapi/asm/kvm.h
> @@ -204,6 +204,7 @@ 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 50be079b5528..0748810c0252 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..b0f66c7bf010
> --- /dev/null
> +++ b/arch/riscv/kvm/vcpu_sbi_fwft.c
> @@ -0,0 +1,216 @@
> +// 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>
> +
> +struct kvm_sbi_fwft_feature {
> +       /**
> +        * @id: Feature ID
> +        */
> +       enum sbi_fwft_feature_t id;
> +
> +       /**
> +        * @supported: Check if the feature is supported on the vcpu
> +        *
> +        * This callback is optional, if not provided the feature is assumed to
> +        * be supported
> +        */
> +       bool (*supported)(struct kvm_vcpu *vcpu);
> +
> +       /**
> +        * @set: Set the feature value
> +        *
> +        * Return SBI_SUCCESS on success or an SBI error (SBI_ERR_*)
> +        *
> +        * This callback is mandatory
> +        */
> +       long (*set)(struct kvm_vcpu *vcpu, struct kvm_sbi_fwft_config *conf, unsigned long value);
> +
> +       /**
> +        * @get: Get the feature current value
> +        *
> +        * Return SBI_SUCCESS on success or an SBI error (SBI_ERR_*)
> +        *
> +        * This callback is mandatory
> +        */
> +       long (*get)(struct kvm_vcpu *vcpu, struct kvm_sbi_fwft_config *conf, unsigned long *value);
> +};
> +
> +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;
> +       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, u32 feature,
> +                               struct kvm_sbi_fwft_config **conf)
> +{
> +       struct kvm_sbi_fwft_config *tconf;
> +
> +       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, u32 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;
> +       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;
> +       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,
> +};
> --
> 2.49.0
>

2025-05-23T12:19:30+02:00, Clément Léger <cleger@rivosinc.com>:
> +++ b/arch/riscv/kvm/vcpu_sbi_fwft.c
> +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,
> +};

How will userspace control which subset of these features is allowed in
the guest?

(We can reuse the KVM SBI extension interface if we don't want to add a
 FWFT specific ONE_REG.)

Thanks.

On 23/05/2025 15:05, Radim Krčmář wrote:
> 2025-05-23T12:19:30+02:00, Clément Léger <cleger@rivosinc.com>:
>> +++ b/arch/riscv/kvm/vcpu_sbi_fwft.c
>> +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,
>> +};
> 
> How will userspace control which subset of these features is allowed in
> the guest?
> 
> (We can reuse the KVM SBI extension interface if we don't want to add a
>  FWFT specific ONE_REG.)

Hi Radim,

I didn't looked at that part. But most likely using the kvm one reg
interface seems ok like what is done for STA ? We could have per feature
override with one reg per feature.

Is this something blocking though ? We'd like to merge FWFT once SBI 3.0
is ratified so that would be nice not delaying it too much. I'll take a
look at it to see if it isn't too long to implement.

Thanks,

Clément

> 
> Thanks.

2025-05-23T17:29:49+02:00, Clément Léger <cleger@rivosinc.com>:
> On 23/05/2025 15:05, Radim Krčmář wrote:
>> 2025-05-23T12:19:30+02:00, Clément Léger <cleger@rivosinc.com>:
>>> +++ b/arch/riscv/kvm/vcpu_sbi_fwft.c
>>> +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,
>>> +};
>> 
>> How will userspace control which subset of these features is allowed in
>> the guest?
>> 
>> (We can reuse the KVM SBI extension interface if we don't want to add a
>>  FWFT specific ONE_REG.)
>
> Hi Radim,
>
> I didn't looked at that part. But most likely using the kvm one reg
> interface seems ok like what is done for STA ? We could have per feature
> override with one reg per feature.

Sounds fine.

> Is this something blocking though ? We'd like to merge FWFT once SBI 3.0
> is ratified so that would be nice not delaying it too much. I'll take a
> look at it to see if it isn't too long to implement.

Not blocking, but I would at least default FWFT to disabled, because
current userspace cannot handle [14/14].  (Well... save/restore was
probably broken even before, but let's try to not make it worse. :])

Thanks.

On 5/23/25 9:27 AM, Radim KrÄmáŠwrote:
> 2025-05-23T17:29:49+02:00, Clément Léger <cleger@rivosinc.com>:
>> On 23/05/2025 15:05, Radim Krčmář wrote:
>>> 2025-05-23T12:19:30+02:00, Clément Léger <cleger@rivosinc.com>:
>>>> +++ b/arch/riscv/kvm/vcpu_sbi_fwft.c
>>>> +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,
>>>> +};
>>>
>>> How will userspace control which subset of these features is allowed in
>>> the guest?
>>>
>>> (We can reuse the KVM SBI extension interface if we don't want to add a
>>>   FWFT specific ONE_REG.)
>>
>> Hi Radim,
>>
>> I didn't looked at that part. But most likely using the kvm one reg
>> interface seems ok like what is done for STA ? We could have per feature
>> override with one reg per feature.
> 
> Sounds fine.
> 

Yeah. We can have a follow up series for SBI FWFT state that allows user 
space to toggle each state individually.

>> Is this something blocking though ? We'd like to merge FWFT once SBI 3.0
>> is ratified so that would be nice not delaying it too much. I'll take a
>> look at it to see if it isn't too long to implement.
> 
> Not blocking, but I would at least default FWFT to disabled, because
> current userspace cannot handle [14/14].  (Well... save/restore was
> probably broken even before, but let's try to not make it worse. :])
> 

User space can not enable or disable misaligned access delegation as 
there is no interface for now rightly pointed by you. I guess supporting 
that would be quicker than fixing the broader guest save/restore 
anyways. Isn't it ?

We can have the patches ready for the next MW for FWFT one reg interface.

> Thanks.
> 
> _______________________________________________
> linux-riscv mailing list
> linux-riscv@lists.infradead.org
> http://lists.infradead.org/mailman/listinfo/linux-riscv

2025-05-23T11:02:11-07:00, Atish Patra <atish.patra@linux.dev>:
> On 5/23/25 9:27 AM, Radim KrÄmáŠwrote:
>> 2025-05-23T17:29:49+02:00, Clément Léger <cleger@rivosinc.com>:
>>> Is this something blocking though ? We'd like to merge FWFT once SBI 3.0
>>> is ratified so that would be nice not delaying it too much. I'll take a
>>> look at it to see if it isn't too long to implement.
>> 
>> Not blocking, but I would at least default FWFT to disabled, because
>> current userspace cannot handle [14/14].  (Well... save/restore was
>> probably broken even before, but let's try to not make it worse. :])
>> 
>
> User space can not enable or disable misaligned access delegation as 
> there is no interface for now rightly pointed by you.

I mean setting default_disabled=true and just disabling FWFT for the
guest unless userspace explicitly enables the incomplete extension.
We would blame the user for wanting mutually exclusive features.

>                                                       I guess supporting 
> that would be quicker than fixing the broader guest save/restore 
> anyways. Isn't it ?

Yes.  The save/restore for FWFT is simple (if we disregard the
discussions), but definitely more than a single line.

On 23/05/2025 20:02, Atish Patra wrote:
> On 5/23/25 9:27 AM, Radim KrÄmáŠwrote:
>> 2025-05-23T17:29:49+02:00, Clément Léger <cleger@rivosinc.com>:
>>> On 23/05/2025 15:05, Radim Krčmář wrote:
>>>> 2025-05-23T12:19:30+02:00, Clément Léger <cleger@rivosinc.com>:
>>>>> +++ b/arch/riscv/kvm/vcpu_sbi_fwft.c
>>>>> +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,
>>>>> +};
>>>>
>>>> How will userspace control which subset of these features is allowed in
>>>> the guest?
>>>>
>>>> (We can reuse the KVM SBI extension interface if we don't want to add a
>>>>   FWFT specific ONE_REG.)
>>>
>>> Hi Radim,
>>>
>>> I didn't looked at that part. But most likely using the kvm one reg
>>> interface seems ok like what is done for STA ? We could have per feature
>>> override with one reg per feature.
>>
>> Sounds fine.
>>
> 
> Yeah. We can have a follow up series for SBI FWFT state that allows user
> space to toggle each state individually.
> 
>>> Is this something blocking though ? We'd like to merge FWFT once SBI 3.0
>>> is ratified so that would be nice not delaying it too much. I'll take a
>>> look at it to see if it isn't too long to implement.
>>
>> Not blocking, but I would at least default FWFT to disabled, because
>> current userspace cannot handle [14/14].  (Well... save/restore was
>> probably broken even before, but let's try to not make it worse. :])
>>
> 
> User space can not enable or disable misaligned access delegation as
> there is no interface for now rightly pointed by you. I guess supporting
> that would be quicker than fixing the broader guest save/restore
> anyways. Isn't it ?
> 
> We can have the patches ready for the next MW for FWFT one reg interface.

Yeah sure I'll work on that in the meantime.

> 
>> Thanks.
>>
>> _______________________________________________
>> linux-riscv mailing list
>> linux-riscv@lists.infradead.org
>> http://lists.infradead.org/mailman/listinfo/linux-riscv
>