Implement support for the HVMOP_set_evtchn_upcall_vector hypercall in
order to set the per-vCPU event channel vector callback on Linux and
use it in preference of HVM_PARAM_CALLBACK_IRQ.

If the per-VCPU vector setup is successful on BSP, use this method
for the APs. If not, fallback to the global vector-type callback.

Also register callback_irq at per-vCPU event channel setup to trick
toolstack to think the domain is enlightened.

Suggested-by: "Roger Pau Monné" <roger.pau@citrix.com>
Signed-off-by: Jane Malalane <jane.malalane@citrix.com>
---
CC: Juergen Gross <jgross@suse.com>
CC: Boris Ostrovsky <boris.ostrovsky@oracle.com>
CC: Thomas Gleixner <tglx@linutronix.de>
CC: Ingo Molnar <mingo@redhat.com>
CC: Borislav Petkov <bp@alien8.de>
CC: Dave Hansen <dave.hansen@linux.intel.com>
CC: x86@kernel.org
CC: "H. Peter Anvin" <hpa@zytor.com>
CC: Stefano Stabellini <sstabellini@kernel.org>
CC: Oleksandr Tyshchenko <oleksandr_tyshchenko@epam.com>
CC: Jane Malalane <jane.malalane@citrix.com>
CC: Maximilian Heyne <mheyne@amazon.de>
CC: Jan Beulich <jbeulich@suse.com>
CC: Colin Ian King <colin.king@intel.com>
CC: xen-devel@lists.xenproject.org

v2:
 * remove no_vector_callback
 * make xen_have_vector_callback a bool
 * rename xen_ack_upcall to xen_percpu_upcall
 * fail to bring CPU up on init instead of crashing kernel
 * add and use xen_set_upcall_vector where suitable
 * xen_setup_upcall_vector -> xen_init_setup_upcall_vector for clarity
---
 arch/x86/include/asm/xen/cpuid.h   |  2 ++
 arch/x86/include/asm/xen/events.h  |  3 ++-
 arch/x86/xen/enlighten.c           |  2 +-
 arch/x86/xen/enlighten_hvm.c       | 24 ++++++++++++++-----
 arch/x86/xen/suspend_hvm.c         | 10 +++++++-
 drivers/xen/events/events_base.c   | 49 ++++++++++++++++++++++++++++++++++----
 include/xen/hvm.h                  |  2 ++
 include/xen/interface/hvm/hvm_op.h | 15 ++++++++++++
 8 files changed, 93 insertions(+), 14 deletions(-)

diff --git a/arch/x86/include/asm/xen/cpuid.h b/arch/x86/include/asm/xen/cpuid.h
index 78e667a31d6c..6daa9b0c8d11 100644
--- a/arch/x86/include/asm/xen/cpuid.h
+++ b/arch/x86/include/asm/xen/cpuid.h
@@ -107,6 +107,8 @@
  * ID field from 8 to 15 bits, allowing to target APIC IDs up 32768.
  */
 #define XEN_HVM_CPUID_EXT_DEST_ID      (1u << 5)
+/* Per-vCPU event channel upcalls */
+#define XEN_HVM_CPUID_UPCALL_VECTOR    (1u << 6)
 
 /*
  * Leaf 6 (0x40000x05)
diff --git a/arch/x86/include/asm/xen/events.h b/arch/x86/include/asm/xen/events.h
index 068d9b067c83..62bdceb594f1 100644
--- a/arch/x86/include/asm/xen/events.h
+++ b/arch/x86/include/asm/xen/events.h
@@ -23,7 +23,7 @@ static inline int xen_irqs_disabled(struct pt_regs *regs)
 /* No need for a barrier -- XCHG is a barrier on x86. */
 #define xchg_xen_ulong(ptr, val) xchg((ptr), (val))
 
-extern int xen_have_vector_callback;
+extern bool xen_have_vector_callback;
 
 /*
  * Events delivered via platform PCI interrupts are always
@@ -34,4 +34,5 @@ static inline bool xen_support_evtchn_rebind(void)
 	return (!xen_hvm_domain() || xen_have_vector_callback);
 }
 
+extern bool xen_percpu_upcall;
 #endif /* _ASM_X86_XEN_EVENTS_H */
diff --git a/arch/x86/xen/enlighten.c b/arch/x86/xen/enlighten.c
index 30c6e986a6cd..b8db2148c07d 100644
--- a/arch/x86/xen/enlighten.c
+++ b/arch/x86/xen/enlighten.c
@@ -51,7 +51,7 @@ EXPORT_SYMBOL_GPL(xen_start_info);
 
 struct shared_info xen_dummy_shared_info;
 
-__read_mostly int xen_have_vector_callback;
+__read_mostly bool xen_have_vector_callback = true;
 EXPORT_SYMBOL_GPL(xen_have_vector_callback);
 
 /*
diff --git a/arch/x86/xen/enlighten_hvm.c b/arch/x86/xen/enlighten_hvm.c
index 8b71b1dd7639..198d3cd3e9a5 100644
--- a/arch/x86/xen/enlighten_hvm.c
+++ b/arch/x86/xen/enlighten_hvm.c
@@ -7,6 +7,8 @@
 
 #include <xen/features.h>
 #include <xen/events.h>
+#include <xen/hvm.h>
+#include <xen/interface/hvm/hvm_op.h>
 #include <xen/interface/memory.h>
 
 #include <asm/apic.h>
@@ -30,6 +32,9 @@
 
 static unsigned long shared_info_pfn;
 
+__ro_after_init bool xen_percpu_upcall;
+EXPORT_SYMBOL_GPL(xen_percpu_upcall);
+
 void xen_hvm_init_shared_info(void)
 {
 	struct xen_add_to_physmap xatp;
@@ -125,6 +130,9 @@ DEFINE_IDTENTRY_SYSVEC(sysvec_xen_hvm_callback)
 {
 	struct pt_regs *old_regs = set_irq_regs(regs);
 
+	if (xen_percpu_upcall)
+		ack_APIC_irq();
+
 	inc_irq_stat(irq_hv_callback_count);
 
 	xen_hvm_evtchn_do_upcall();
@@ -168,6 +176,15 @@ static int xen_cpu_up_prepare_hvm(unsigned int cpu)
 	if (!xen_have_vector_callback)
 		return 0;
 
+	if (xen_percpu_upcall) {
+		rc = xen_set_upcall_vector(cpu);
+		if (rc) {
+			WARN(1, "HVMOP_set_evtchn_upcall_vector"
+			     " for CPU %d failed: %d\n", cpu, rc);
+			return rc;
+		}
+	}
+
 	if (xen_feature(XENFEAT_hvm_safe_pvclock))
 		xen_setup_timer(cpu);
 
@@ -188,8 +205,6 @@ static int xen_cpu_dead_hvm(unsigned int cpu)
 	return 0;
 }
 
-static bool no_vector_callback __initdata;
-
 static void __init xen_hvm_guest_init(void)
 {
 	if (xen_pv_domain())
@@ -211,9 +226,6 @@ static void __init xen_hvm_guest_init(void)
 
 	xen_panic_handler_init();
 
-	if (!no_vector_callback && xen_feature(XENFEAT_hvm_callback_vector))
-		xen_have_vector_callback = 1;
-
 	xen_hvm_smp_init();
 	WARN_ON(xen_cpuhp_setup(xen_cpu_up_prepare_hvm, xen_cpu_dead_hvm));
 	xen_unplug_emulated_devices();
@@ -239,7 +251,7 @@ early_param("xen_nopv", xen_parse_nopv);
 
 static __init int xen_parse_no_vector_callback(char *arg)
 {
-	no_vector_callback = true;
+	xen_have_vector_callback = false;
 	return 0;
 }
 early_param("xen_no_vector_callback", xen_parse_no_vector_callback);
diff --git a/arch/x86/xen/suspend_hvm.c b/arch/x86/xen/suspend_hvm.c
index 9d548b0c772f..0c4f7554b7cc 100644
--- a/arch/x86/xen/suspend_hvm.c
+++ b/arch/x86/xen/suspend_hvm.c
@@ -5,6 +5,7 @@
 #include <xen/hvm.h>
 #include <xen/features.h>
 #include <xen/interface/features.h>
+#include <xen/events.h>
 
 #include "xen-ops.h"
 
@@ -14,6 +15,13 @@ void xen_hvm_post_suspend(int suspend_cancelled)
 		xen_hvm_init_shared_info();
 		xen_vcpu_restore();
 	}
-	xen_setup_callback_vector();
+	if (xen_percpu_upcall) {
+		unsigned int cpu;
+
+		for_each_online_cpu(cpu)
+			BUG_ON(xen_set_upcall_vector(cpu));
+	} else {
+		xen_setup_callback_vector();
+	}
 	xen_unplug_emulated_devices();
 }
diff --git a/drivers/xen/events/events_base.c b/drivers/xen/events/events_base.c
index 46d9295d9a6e..2ad93595d03a 100644
--- a/drivers/xen/events/events_base.c
+++ b/drivers/xen/events/events_base.c
@@ -48,6 +48,7 @@
 #include <asm/xen/pci.h>
 #endif
 #include <asm/sync_bitops.h>
+#include <asm/xen/cpuid.h>
 #include <asm/xen/hypercall.h>
 #include <asm/xen/hypervisor.h>
 #include <xen/page.h>
@@ -2195,11 +2196,48 @@ void xen_setup_callback_vector(void)
 		callback_via = HVM_CALLBACK_VECTOR(HYPERVISOR_CALLBACK_VECTOR);
 		if (xen_set_callback_via(callback_via)) {
 			pr_err("Request for Xen HVM callback vector failed\n");
-			xen_have_vector_callback = 0;
+			xen_have_vector_callback = false;
 		}
 	}
 }
 
+/* Setup per-vCPU vector-type callbacks and trick toolstack to think
+ * we are enlightened. If this setup is unavailable, fallback to the
+ * global vector-type callback. */
+static __init void xen_init_setup_upcall_vector(void)
+{
+	unsigned int cpu = 0;
+
+	if (!xen_have_vector_callback)
+		return;
+
+	if ((cpuid_eax(xen_cpuid_base() + 4) & XEN_HVM_CPUID_UPCALL_VECTOR) &&
+	    !xen_set_upcall_vector(cpu) && !xen_set_callback_via(1))
+		xen_percpu_upcall = true;
+	else if (xen_feature(XENFEAT_hvm_callback_vector))
+		xen_setup_callback_vector();
+	else
+		xen_have_vector_callback = false;
+}
+
+int xen_set_upcall_vector(unsigned int cpu)
+{
+	int rc;
+	xen_hvm_evtchn_upcall_vector_t op = {
+		.vector = HYPERVISOR_CALLBACK_VECTOR,
+		.vcpu = per_cpu(xen_vcpu_id, cpu),
+	};
+
+	rc = HYPERVISOR_hvm_op(HVMOP_set_evtchn_upcall_vector, &op);
+	if (rc)
+		return rc;
+
+	if (!cpu)
+		rc = xen_set_callback_via(1);
+
+	return rc;
+}
+
 static __init void xen_alloc_callback_vector(void)
 {
 	if (!xen_have_vector_callback)
@@ -2210,6 +2248,8 @@ static __init void xen_alloc_callback_vector(void)
 }
 #else
 void xen_setup_callback_vector(void) {}
+static inline void xen_init_setup_upcall_vector(void) {}
+int xen_set_upcall_vector(unsigned int cpu) {}
 static inline void xen_alloc_callback_vector(void) {}
 #endif
 
@@ -2271,10 +2311,9 @@ void __init xen_init_IRQ(void)
 		if (xen_initial_domain())
 			pci_xen_initial_domain();
 	}
-	if (xen_feature(XENFEAT_hvm_callback_vector)) {
-		xen_setup_callback_vector();
-		xen_alloc_callback_vector();
-	}
+	xen_init_setup_upcall_vector();
+	xen_alloc_callback_vector();
+
 
 	if (xen_hvm_domain()) {
 		native_init_IRQ();
diff --git a/include/xen/hvm.h b/include/xen/hvm.h
index b7fd7fc9ad41..8da7a6747058 100644
--- a/include/xen/hvm.h
+++ b/include/xen/hvm.h
@@ -60,4 +60,6 @@ static inline int hvm_get_parameter(int idx, uint64_t *value)
 
 void xen_setup_callback_vector(void);
 
+int xen_set_upcall_vector(unsigned int cpu);
+
 #endif /* XEN_HVM_H__ */
diff --git a/include/xen/interface/hvm/hvm_op.h b/include/xen/interface/hvm/hvm_op.h
index f3097e79bb03..e714d8b6ef89 100644
--- a/include/xen/interface/hvm/hvm_op.h
+++ b/include/xen/interface/hvm/hvm_op.h
@@ -46,4 +46,19 @@ struct xen_hvm_get_mem_type {
 };
 DEFINE_GUEST_HANDLE_STRUCT(xen_hvm_get_mem_type);
 
+/*
+ * HVMOP_set_evtchn_upcall_vector: Set a <vector> that should be used for event
+ *                                 channel upcalls on the specified <vcpu>. If set,
+ *                                 this vector will be used in preference to the
+ *                                 domain global callback via (see
+ *                                 HVM_PARAM_CALLBACK_IRQ).
+ */
+#define HVMOP_set_evtchn_upcall_vector 23
+struct xen_hvm_evtchn_upcall_vector {
+    uint32_t vcpu;
+    uint8_t vector;
+};
+typedef struct xen_hvm_evtchn_upcall_vector xen_hvm_evtchn_upcall_vector_t;
+DEFINE_GUEST_HANDLE_STRUCT(xen_hvm_evtchn_upcall_vector_t);
+
 #endif /* __XEN_PUBLIC_HVM_HVM_OP_H__ */
-- 
2.11.0

Hi Jane,

On 26/07/2022 13:56, Jane Malalane wrote:
> diff --git a/arch/x86/xen/suspend_hvm.c b/arch/x86/xen/suspend_hvm.c
> index 9d548b0c772f..0c4f7554b7cc 100644
> --- a/arch/x86/xen/suspend_hvm.c
> +++ b/arch/x86/xen/suspend_hvm.c
> @@ -5,6 +5,7 @@
>   #include <xen/hvm.h>
>   #include <xen/features.h>
>   #include <xen/interface/features.h>
> +#include <xen/events.h>
>   
>   #include "xen-ops.h"
>   
> @@ -14,6 +15,13 @@ void xen_hvm_post_suspend(int suspend_cancelled)
>   		xen_hvm_init_shared_info();
>   		xen_vcpu_restore();
>   	}
> -	xen_setup_callback_vector();
> +	if (xen_percpu_upcall) {
> +		unsigned int cpu;
> +
> +		for_each_online_cpu(cpu)
> +			BUG_ON(xen_set_upcall_vector(cpu));
> +	} else {
> +		xen_setup_callback_vector();
> +	}
>   	xen_unplug_emulated_devices();
>   }
> diff --git a/drivers/xen/events/events_base.c b/drivers/xen/events/events_base.c
> index 46d9295d9a6e..2ad93595d03a 100644
> --- a/drivers/xen/events/events_base.c
> +++ b/drivers/xen/events/events_base.c
> @@ -48,6 +48,7 @@
>   #include <asm/xen/pci.h>
>   #endif
>   #include <asm/sync_bitops.h>
> +#include <asm/xen/cpuid.h>

This include doesn't exist on Arm and will result to a build failure:

linux/drivers/xen/events/events_base.c:51:10: fatal error: 
asm/xen/cpuid.h: No such file or directory
    51 | #include <asm/xen/cpuid.h>
       |          ^~~~~~~~~~~~~~~~~


>   #include <asm/xen/hypercall.h>
>   #include <asm/xen/hypervisor.h>
>   #include <xen/page.h>
> @@ -2195,11 +2196,48 @@ void xen_setup_callback_vector(void)
>   		callback_via = HVM_CALLBACK_VECTOR(HYPERVISOR_CALLBACK_VECTOR);
>   		if (xen_set_callback_via(callback_via)) {
>   			pr_err("Request for Xen HVM callback vector failed\n");
> -			xen_have_vector_callback = 0;
> +			xen_have_vector_callback = false;
>   		}
>   	}
>   }
>   
> +/* Setup per-vCPU vector-type callbacks and trick toolstack to think
> + * we are enlightened. If this setup is unavailable, fallback to the
> + * global vector-type callback. */
> +static __init void xen_init_setup_upcall_vector(void)
> +{
> +	unsigned int cpu = 0;
> +
> +	if (!xen_have_vector_callback)
> +		return;
> +
> +	if ((cpuid_eax(xen_cpuid_base() + 4) & XEN_HVM_CPUID_UPCALL_VECTOR) &&
> +	    !xen_set_upcall_vector(cpu) && !xen_set_callback_via(1))

xen_cpuid_base() is an x86-ism. This is going to build because 
CONFIG_XEN_PVHVM is only set for x86. However, I think this is quite 
fragile.

You are also using more variable defined only on x86. So it feels to me 
that these functions should be implemented in x86 code.

> +		xen_percpu_upcall = true;
> +	else if (xen_feature(XENFEAT_hvm_callback_vector))
> +		xen_setup_callback_vector();
> +	else
> +		xen_have_vector_callback = false;
> +}
> +
> +int xen_set_upcall_vector(unsigned int cpu)
> +{
> +	int rc;
> +	xen_hvm_evtchn_upcall_vector_t op = {
> +		.vector = HYPERVISOR_CALLBACK_VECTOR,
> +		.vcpu = per_cpu(xen_vcpu_id, cpu),
> +	};
> +
> +	rc = HYPERVISOR_hvm_op(HVMOP_set_evtchn_upcall_vector, &op);
> +	if (rc)
> +		return rc;
> +
> +	if (!cpu)
> +		rc = xen_set_callback_via(1);
> +
> +	return rc;
> +}
> +
>   static __init void xen_alloc_callback_vector(void)
>   {
>   	if (!xen_have_vector_callback)
> @@ -2210,6 +2248,8 @@ static __init void xen_alloc_callback_vector(void)
>   }
>   #else
>   void xen_setup_callback_vector(void) {}
> +static inline void xen_init_setup_upcall_vector(void) {}
> +int xen_set_upcall_vector(unsigned int cpu) {}
>   static inline void xen_alloc_callback_vector(void) {}
>   #endif
>   
> @@ -2271,10 +2311,9 @@ void __init xen_init_IRQ(void)
>   		if (xen_initial_domain())
>   			pci_xen_initial_domain();
>   	}
> -	if (xen_feature(XENFEAT_hvm_callback_vector)) {
> -		xen_setup_callback_vector();
> -		xen_alloc_callback_vector();
> -	}
> +	xen_init_setup_upcall_vector();
> +	xen_alloc_callback_vector();
> +
>   
>   	if (xen_hvm_domain()) {
>   		native_init_IRQ();
> diff --git a/include/xen/hvm.h b/include/xen/hvm.h
> index b7fd7fc9ad41..8da7a6747058 100644
> --- a/include/xen/hvm.h
> +++ b/include/xen/hvm.h
> @@ -60,4 +60,6 @@ static inline int hvm_get_parameter(int idx, uint64_t *value)
>   
>   void xen_setup_callback_vector(void);
>   
> +int xen_set_upcall_vector(unsigned int cpu);
> +
>   #endif /* XEN_HVM_H__ */
> diff --git a/include/xen/interface/hvm/hvm_op.h b/include/xen/interface/hvm/hvm_op.h
> index f3097e79bb03..e714d8b6ef89 100644
> --- a/include/xen/interface/hvm/hvm_op.h
> +++ b/include/xen/interface/hvm/hvm_op.h
> @@ -46,4 +46,19 @@ struct xen_hvm_get_mem_type {
>   };
>   DEFINE_GUEST_HANDLE_STRUCT(xen_hvm_get_mem_type);
>   
> +/*
> + * HVMOP_set_evtchn_upcall_vector: Set a <vector> that should be used for event
> + *                                 channel upcalls on the specified <vcpu>. If set,
> + *                                 this vector will be used in preference to the
> + *                                 domain global callback via (see
> + *                                 HVM_PARAM_CALLBACK_IRQ).
> + */

Technically this hypercall is x86 specific. IOW, it would be possible 
for another architecture to define 23 for something different.

If it is not possible (or desired) to surround with an #ifdef, then I 
think we should at least be mentioned it in the comment.

Cheers,

-- 
Julien Grall

On 27/07/2022 13:32, Julien Grall wrote:
> [CAUTION - EXTERNAL EMAIL] DO NOT reply, click links, or open 
> attachments unless you have verified the sender and know the content is 
> safe.
> 
> Hi Jane,
> 
> On 26/07/2022 13:56, Jane Malalane wrote:
>> diff --git a/arch/x86/xen/suspend_hvm.c b/arch/x86/xen/suspend_hvm.c
>> index 9d548b0c772f..0c4f7554b7cc 100644
>> --- a/arch/x86/xen/suspend_hvm.c
>> +++ b/arch/x86/xen/suspend_hvm.c
>> @@ -5,6 +5,7 @@
>>   #include <xen/hvm.h>
>>   #include <xen/features.h>
>>   #include <xen/interface/features.h>
>> +#include <xen/events.h>
>>   #include "xen-ops.h"
>> @@ -14,6 +15,13 @@ void xen_hvm_post_suspend(int suspend_cancelled)
>>           xen_hvm_init_shared_info();
>>           xen_vcpu_restore();
>>       }
>> -    xen_setup_callback_vector();
>> +    if (xen_percpu_upcall) {
>> +        unsigned int cpu;
>> +
>> +        for_each_online_cpu(cpu)
>> +            BUG_ON(xen_set_upcall_vector(cpu));
>> +    } else {
>> +        xen_setup_callback_vector();
>> +    }
>>       xen_unplug_emulated_devices();
>>   }
>> diff --git a/drivers/xen/events/events_base.c 
>> b/drivers/xen/events/events_base.c
>> index 46d9295d9a6e..2ad93595d03a 100644
>> --- a/drivers/xen/events/events_base.c
>> +++ b/drivers/xen/events/events_base.c
>> @@ -48,6 +48,7 @@
>>   #include <asm/xen/pci.h>
>>   #endif
>>   #include <asm/sync_bitops.h>
>> +#include <asm/xen/cpuid.h>
> 
> This include doesn't exist on Arm and will result to a build failure:
> 
> linux/drivers/xen/events/events_base.c:51:10: fatal error: 
> asm/xen/cpuid.h: No such file or directory
>     51 | #include <asm/xen/cpuid.h>
>        |          ^~~~~~~~~~~~~~~~~
Thanks, will place it inside the #ifdef CONFIG_X86.
> 
>>   #include <asm/xen/hypercall.h>
>>   #include <asm/xen/hypervisor.h>
>>   #include <xen/page.h>
>> @@ -2195,11 +2196,48 @@ void xen_setup_callback_vector(void)
>>           callback_via = HVM_CALLBACK_VECTOR(HYPERVISOR_CALLBACK_VECTOR);
>>           if (xen_set_callback_via(callback_via)) {
>>               pr_err("Request for Xen HVM callback vector failed\n");
>> -            xen_have_vector_callback = 0;
>> +            xen_have_vector_callback = false;
>>           }
>>       }
>>   }
>> +/* Setup per-vCPU vector-type callbacks and trick toolstack to think
>> + * we are enlightened. If this setup is unavailable, fallback to the
>> + * global vector-type callback. */
>> +static __init void xen_init_setup_upcall_vector(void)
>> +{
>> +    unsigned int cpu = 0;
>> +
>> +    if (!xen_have_vector_callback)
>> +        return;
>> +
>> +    if ((cpuid_eax(xen_cpuid_base() + 4) & 
>> XEN_HVM_CPUID_UPCALL_VECTOR) &&
>> +        !xen_set_upcall_vector(cpu) && !xen_set_callback_via(1))
> 
> xen_cpuid_base() is an x86-ism. This is going to build because 
> CONFIG_XEN_PVHVM is only set for x86. However, I think this is quite 
> fragile.
> 
> You are also using more variable defined only on x86. So it feels to me 
> that these functions should be implemented in x86 code.
I can surround those 4 callback/upcall functions with an ##ifdef.>> 
+        xen_percpu_upcall = true;
>> +    else if (xen_feature(XENFEAT_hvm_callback_vector))
>> +        xen_setup_callback_vector();
>> +    else
>> +        xen_have_vector_callback = false;
>> +}
>> +
>> +int xen_set_upcall_vector(unsigned int cpu)
>> +{
>> +    int rc;
>> +    xen_hvm_evtchn_upcall_vector_t op = {
>> +        .vector = HYPERVISOR_CALLBACK_VECTOR,
>> +        .vcpu = per_cpu(xen_vcpu_id, cpu),
>> +    };
>> +
>> +    rc = HYPERVISOR_hvm_op(HVMOP_set_evtchn_upcall_vector, &op);
>> +    if (rc)
>> +        return rc;
>> +
>> +    if (!cpu)
>> +        rc = xen_set_callback_via(1);
>> +
>> +    return rc;
>> +}
>> +
>>   static __init void xen_alloc_callback_vector(void)
>>   {
>>       if (!xen_have_vector_callback)
>> @@ -2210,6 +2248,8 @@ static __init void xen_alloc_callback_vector(void)
>>   }
>>   #else
>>   void xen_setup_callback_vector(void) {}
>> +static inline void xen_init_setup_upcall_vector(void) {}
>> +int xen_set_upcall_vector(unsigned int cpu) {}
>>   static inline void xen_alloc_callback_vector(void) {}
>>   #endif
>> @@ -2271,10 +2311,9 @@ void __init xen_init_IRQ(void)
>>           if (xen_initial_domain())
>>               pci_xen_initial_domain();
>>       }
>> -    if (xen_feature(XENFEAT_hvm_callback_vector)) {
>> -        xen_setup_callback_vector();
>> -        xen_alloc_callback_vector();
>> -    }
>> +    xen_init_setup_upcall_vector();
>> +    xen_alloc_callback_vector();
>> +
>>       if (xen_hvm_domain()) {
>>           native_init_IRQ();
>> diff --git a/include/xen/hvm.h b/include/xen/hvm.h
>> index b7fd7fc9ad41..8da7a6747058 100644
>> --- a/include/xen/hvm.h
>> +++ b/include/xen/hvm.h
>> @@ -60,4 +60,6 @@ static inline int hvm_get_parameter(int idx, 
>> uint64_t *value)
>>   void xen_setup_callback_vector(void);
>> +int xen_set_upcall_vector(unsigned int cpu);
>> +
>>   #endif /* XEN_HVM_H__ */
>> diff --git a/include/xen/interface/hvm/hvm_op.h 
>> b/include/xen/interface/hvm/hvm_op.h
>> index f3097e79bb03..e714d8b6ef89 100644
>> --- a/include/xen/interface/hvm/hvm_op.h
>> +++ b/include/xen/interface/hvm/hvm_op.h
>> @@ -46,4 +46,19 @@ struct xen_hvm_get_mem_type {
>>   };
>>   DEFINE_GUEST_HANDLE_STRUCT(xen_hvm_get_mem_type);
>> +/*
>> + * HVMOP_set_evtchn_upcall_vector: Set a <vector> that should be used 
>> for event
>> + *                                 channel upcalls on the specified 
>> <vcpu>. If set,
>> + *                                 this vector will be used in 
>> preference to the
>> + *                                 domain global callback via (see
>> + *                                 HVM_PARAM_CALLBACK_IRQ).
>> + */
> 
> Technically this hypercall is x86 specific. IOW, it would be possible 
> for another architecture to define 23 for something different.
> 
> If it is not possible (or desired) to surround with an #ifdef, then I 
> think we should at least be mentioned it in the comment.
In Xen it is surrounded with an #ifdef. I am happy to do so here too, 
unless there is any opposition.

Thank you,

Jane.

On 7/26/22 8:56 AM, Jane Malalane wrote:
>   
> +/* Setup per-vCPU vector-type callbacks and trick toolstack to think
> + * we are enlightened. If this setup is unavailable, fallback to the
> + * global vector-type callback. */


Comment style.


> +static __init void xen_init_setup_upcall_vector(void)
> +{
> +	unsigned int cpu = 0;


Unnecessary variable.


> +
> +	if (!xen_have_vector_callback)
> +		return;
> +
> +	if ((cpuid_eax(xen_cpuid_base() + 4) & XEN_HVM_CPUID_UPCALL_VECTOR) &&
> +	    !xen_set_upcall_vector(cpu) && !xen_set_callback_via(1))
> +		xen_percpu_upcall = true;
> +	else if (xen_feature(XENFEAT_hvm_callback_vector))
> +		xen_setup_callback_vector();
> +	else
> +		xen_have_vector_callback = false;
> +}
> +
> +int xen_set_upcall_vector(unsigned int cpu)
> +{
> +	int rc;
> +	xen_hvm_evtchn_upcall_vector_t op = {
> +		.vector = HYPERVISOR_CALLBACK_VECTOR,
> +		.vcpu = per_cpu(xen_vcpu_id, cpu),
> +	};
> +
> +	rc = HYPERVISOR_hvm_op(HVMOP_set_evtchn_upcall_vector, &op);
> +	if (rc)
> +		return rc;
> +
> +	if (!cpu)


A comment (e.g. "Let toolstack know that we are enlightened." or something along these lines) would be useful here.


-boris


> +		rc = xen_set_callback_via(1);
> +

On 27/07/2022 00:31, Boris Ostrovsky wrote:
> [CAUTION - EXTERNAL EMAIL] DO NOT reply, click links, or open 
> attachments unless you have verified the sender and know the content is 
> safe.
> 
> On 7/26/22 8:56 AM, Jane Malalane wrote:
>> +/* Setup per-vCPU vector-type callbacks and trick toolstack to think
>> + * we are enlightened. If this setup is unavailable, fallback to the
>> + * global vector-type callback. */
> 
> 
> Comment style.
> 
> 
>> +static __init void xen_init_setup_upcall_vector(void)
>> +{
>> +    unsigned int cpu = 0;
> 
> 
> Unnecessary variable.
> 
> 
>> +
>> +    if (!xen_have_vector_callback)
>> +        return;
>> +
>> +    if ((cpuid_eax(xen_cpuid_base() + 4) & 
>> XEN_HVM_CPUID_UPCALL_VECTOR) &&
>> +        !xen_set_upcall_vector(cpu) && !xen_set_callback_via(1))
>> +        xen_percpu_upcall = true;
>> +    else if (xen_feature(XENFEAT_hvm_callback_vector))
>> +        xen_setup_callback_vector();
>> +    else
>> +        xen_have_vector_callback = false;
>> +}
>> +
>> +int xen_set_upcall_vector(unsigned int cpu)
>> +{
>> +    int rc;
>> +    xen_hvm_evtchn_upcall_vector_t op = {
>> +        .vector = HYPERVISOR_CALLBACK_VECTOR,
>> +        .vcpu = per_cpu(xen_vcpu_id, cpu),
>> +    };
>> +
>> +    rc = HYPERVISOR_hvm_op(HVMOP_set_evtchn_upcall_vector, &op);
>> +    if (rc)
>> +        return rc;
>> +
>> +    if (!cpu)
> 
> 
> A comment (e.g. "Let toolstack know that we are enlightened." or 
> something along these lines) would be useful here.
>Thanks, will include all these changes in a v3.

Jane.

On 26/07/2022 13:56, Jane Malalane wrote:
> Implement support for the HVMOP_set_evtchn_upcall_vector hypercall in
> order to set the per-vCPU event channel vector callback on Linux and
> use it in preference of HVM_PARAM_CALLBACK_IRQ.
> 
> If the per-VCPU vector setup is successful on BSP, use this method
> for the APs. If not, fallback to the global vector-type callback.
> 
> Also register callback_irq at per-vCPU event channel setup to trick
> toolstack to think the domain is enlightened.
> 
> Suggested-by: "Roger Pau Monné" <roger.pau@citrix.com>
> Signed-off-by: Jane Malalane <jane.malalane@citrix.com>
> ---
> CC: Juergen Gross <jgross@suse.com>
> CC: Boris Ostrovsky <boris.ostrovsky@oracle.com>
> CC: Thomas Gleixner <tglx@linutronix.de>
> CC: Ingo Molnar <mingo@redhat.com>
> CC: Borislav Petkov <bp@alien8.de>
> CC: Dave Hansen <dave.hansen@linux.intel.com>
> CC: x86@kernel.org
> CC: "H. Peter Anvin" <hpa@zytor.com>
> CC: Stefano Stabellini <sstabellini@kernel.org>
> CC: Oleksandr Tyshchenko <oleksandr_tyshchenko@epam.com>
> CC: Jane Malalane <jane.malalane@citrix.com>
> CC: Maximilian Heyne <mheyne@amazon.de>
> CC: Jan Beulich <jbeulich@suse.com>
> CC: Colin Ian King <colin.king@intel.com>
> CC: xen-devel@lists.xenproject.org
> 
> v2:
>   * remove no_vector_callback
>   * make xen_have_vector_callback a bool
>   * rename xen_ack_upcall to xen_percpu_upcall
>   * fail to bring CPU up on init instead of crashing kernel
>   * add and use xen_set_upcall_vector where suitable
>   * xen_setup_upcall_vector -> xen_init_setup_upcall_vector for clarity
> ---
>   arch/x86/include/asm/xen/cpuid.h   |  2 ++
>   arch/x86/include/asm/xen/events.h  |  3 ++-
>   arch/x86/xen/enlighten.c           |  2 +-
>   arch/x86/xen/enlighten_hvm.c       | 24 ++++++++++++++-----
>   arch/x86/xen/suspend_hvm.c         | 10 +++++++-
>   drivers/xen/events/events_base.c   | 49 ++++++++++++++++++++++++++++++++++----
>   include/xen/hvm.h                  |  2 ++
>   include/xen/interface/hvm/hvm_op.h | 15 ++++++++++++
>   8 files changed, 93 insertions(+), 14 deletions(-)
> 
> diff --git a/arch/x86/include/asm/xen/cpuid.h b/arch/x86/include/asm/xen/cpuid.h
> index 78e667a31d6c..6daa9b0c8d11 100644
> --- a/arch/x86/include/asm/xen/cpuid.h
> +++ b/arch/x86/include/asm/xen/cpuid.h
> @@ -107,6 +107,8 @@
>    * ID field from 8 to 15 bits, allowing to target APIC IDs up 32768.
>    */
>   #define XEN_HVM_CPUID_EXT_DEST_ID      (1u << 5)
> +/* Per-vCPU event channel upcalls */
> +#define XEN_HVM_CPUID_UPCALL_VECTOR    (1u << 6)
>   
>   /*
>    * Leaf 6 (0x40000x05)
> diff --git a/arch/x86/include/asm/xen/events.h b/arch/x86/include/asm/xen/events.h
> index 068d9b067c83..62bdceb594f1 100644
> --- a/arch/x86/include/asm/xen/events.h
> +++ b/arch/x86/include/asm/xen/events.h
> @@ -23,7 +23,7 @@ static inline int xen_irqs_disabled(struct pt_regs *regs)
>   /* No need for a barrier -- XCHG is a barrier on x86. */
>   #define xchg_xen_ulong(ptr, val) xchg((ptr), (val))
>   
> -extern int xen_have_vector_callback;
> +extern bool xen_have_vector_callback;
>   
>   /*
>    * Events delivered via platform PCI interrupts are always
> @@ -34,4 +34,5 @@ static inline bool xen_support_evtchn_rebind(void)
>   	return (!xen_hvm_domain() || xen_have_vector_callback);
>   }
>   
> +extern bool xen_percpu_upcall;
>   #endif /* _ASM_X86_XEN_EVENTS_H */
> diff --git a/arch/x86/xen/enlighten.c b/arch/x86/xen/enlighten.c
> index 30c6e986a6cd..b8db2148c07d 100644
> --- a/arch/x86/xen/enlighten.c
> +++ b/arch/x86/xen/enlighten.c
> @@ -51,7 +51,7 @@ EXPORT_SYMBOL_GPL(xen_start_info);
>   
>   struct shared_info xen_dummy_shared_info;
>   
> -__read_mostly int xen_have_vector_callback;
> +__read_mostly bool xen_have_vector_callback = true;
>   EXPORT_SYMBOL_GPL(xen_have_vector_callback);
>   
>   /*
> diff --git a/arch/x86/xen/enlighten_hvm.c b/arch/x86/xen/enlighten_hvm.c
> index 8b71b1dd7639..198d3cd3e9a5 100644
> --- a/arch/x86/xen/enlighten_hvm.c
> +++ b/arch/x86/xen/enlighten_hvm.c
> @@ -7,6 +7,8 @@
>   
>   #include <xen/features.h>
>   #include <xen/events.h>
> +#include <xen/hvm.h>
> +#include <xen/interface/hvm/hvm_op.h>
>   #include <xen/interface/memory.h>
>   
>   #include <asm/apic.h>
> @@ -30,6 +32,9 @@
>   
>   static unsigned long shared_info_pfn;
>   
> +__ro_after_init bool xen_percpu_upcall;
> +EXPORT_SYMBOL_GPL(xen_percpu_upcall);
> +
>   void xen_hvm_init_shared_info(void)
>   {
>   	struct xen_add_to_physmap xatp;
> @@ -125,6 +130,9 @@ DEFINE_IDTENTRY_SYSVEC(sysvec_xen_hvm_callback)
>   {
>   	struct pt_regs *old_regs = set_irq_regs(regs);
>   
> +	if (xen_percpu_upcall)
> +		ack_APIC_irq();
> +
>   	inc_irq_stat(irq_hv_callback_count);
>   
>   	xen_hvm_evtchn_do_upcall();
> @@ -168,6 +176,15 @@ static int xen_cpu_up_prepare_hvm(unsigned int cpu)
>   	if (!xen_have_vector_callback)
>   		return 0;
>   
> +	if (xen_percpu_upcall) {
> +		rc = xen_set_upcall_vector(cpu);
> +		if (rc) {
> +			WARN(1, "HVMOP_set_evtchn_upcall_vector"
> +			     " for CPU %d failed: %d\n", cpu, rc);
> +			return rc;
> +		}
> +	}
> +
>   	if (xen_feature(XENFEAT_hvm_safe_pvclock))
>   		xen_setup_timer(cpu);
>   
> @@ -188,8 +205,6 @@ static int xen_cpu_dead_hvm(unsigned int cpu)
>   	return 0;
>   }
>   
> -static bool no_vector_callback __initdata;
> -
>   static void __init xen_hvm_guest_init(void)
>   {
>   	if (xen_pv_domain())
> @@ -211,9 +226,6 @@ static void __init xen_hvm_guest_init(void)
>   
>   	xen_panic_handler_init();
>   
> -	if (!no_vector_callback && xen_feature(XENFEAT_hvm_callback_vector))
> -		xen_have_vector_callback = 1;
> -
>   	xen_hvm_smp_init();
>   	WARN_ON(xen_cpuhp_setup(xen_cpu_up_prepare_hvm, xen_cpu_dead_hvm));
>   	xen_unplug_emulated_devices();
> @@ -239,7 +251,7 @@ early_param("xen_nopv", xen_parse_nopv);
>   
>   static __init int xen_parse_no_vector_callback(char *arg)
>   {
> -	no_vector_callback = true;
> +	xen_have_vector_callback = false;
>   	return 0;
>   }
>   early_param("xen_no_vector_callback", xen_parse_no_vector_callback);
> diff --git a/arch/x86/xen/suspend_hvm.c b/arch/x86/xen/suspend_hvm.c
> index 9d548b0c772f..0c4f7554b7cc 100644
> --- a/arch/x86/xen/suspend_hvm.c
> +++ b/arch/x86/xen/suspend_hvm.c
> @@ -5,6 +5,7 @@
>   #include <xen/hvm.h>
>   #include <xen/features.h>
>   #include <xen/interface/features.h>
> +#include <xen/events.h>
>   
>   #include "xen-ops.h"
>   
> @@ -14,6 +15,13 @@ void xen_hvm_post_suspend(int suspend_cancelled)
>   		xen_hvm_init_shared_info();
>   		xen_vcpu_restore();
>   	}
> -	xen_setup_callback_vector();
> +	if (xen_percpu_upcall) {
> +		unsigned int cpu;
> +
> +		for_each_online_cpu(cpu)
> +			BUG_ON(xen_set_upcall_vector(cpu));
> +	} else {
> +		xen_setup_callback_vector();
> +	}
>   	xen_unplug_emulated_devices();
>   }
> diff --git a/drivers/xen/events/events_base.c b/drivers/xen/events/events_base.c
> index 46d9295d9a6e..2ad93595d03a 100644
> --- a/drivers/xen/events/events_base.c
> +++ b/drivers/xen/events/events_base.c
> @@ -48,6 +48,7 @@
>   #include <asm/xen/pci.h>
>   #endif
>   #include <asm/sync_bitops.h>
> +#include <asm/xen/cpuid.h>
>   #include <asm/xen/hypercall.h>
>   #include <asm/xen/hypervisor.h>
>   #include <xen/page.h>
> @@ -2195,11 +2196,48 @@ void xen_setup_callback_vector(void)
>   		callback_via = HVM_CALLBACK_VECTOR(HYPERVISOR_CALLBACK_VECTOR);
>   		if (xen_set_callback_via(callback_via)) {
>   			pr_err("Request for Xen HVM callback vector failed\n");
> -			xen_have_vector_callback = 0;
> +			xen_have_vector_callback = false;
>   		}
>   	}
>   }
>   
> +/* Setup per-vCPU vector-type callbacks and trick toolstack to think
> + * we are enlightened. If this setup is unavailable, fallback to the
> + * global vector-type callback. */
> +static __init void xen_init_setup_upcall_vector(void)
> +{
> +	unsigned int cpu = 0;
> +
> +	if (!xen_have_vector_callback)
> +		return;
> +
> +	if ((cpuid_eax(xen_cpuid_base() + 4) & XEN_HVM_CPUID_UPCALL_VECTOR) &&
> +	    !xen_set_upcall_vector(cpu) && !xen_set_callback_via(1))
I should have removed xen_set_callback_via(1) here. Will send another 
version, would just like to wait for any comments before I do.

Jane.