Re: [PATCH] kvm: x86: Add logical CPU to KVM_EXIT_FAIL_ENTRY info

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> On 14 Dec 2019, at 1:16, Jim Mattson <jmattson@xxxxxxxxxx> wrote:
> 
> More often than not, a failed VM-entry in a production environment is
> the result of a defective CPU (at least, insofar as Intel x86 is
> concerned). To aid in identifying the bad hardware, add the logical
> CPU to the information provided to userspace on a KVM exit with reason
> KVM_EXIT_FAIL_ENTRY. The presence of this additional information is
> indicated by a new capability, KVM_CAP_FAILED_ENTRY_CPU.
> 
> Signed-off-by: Jim Mattson <jmattson@xxxxxxxxxx>
> Reviewed-by: Peter Shier <pshier@xxxxxxxxxx>
> Reviewed-by: Oliver Upton <oupton@xxxxxxxxxx>
> ---
> Documentation/virt/kvm/api.txt | 1 +
> arch/x86/kvm/svm.c             | 1 +
> arch/x86/kvm/vmx/vmx.c         | 2 ++
> arch/x86/kvm/x86.c             | 1 +
> include/uapi/linux/kvm.h       | 2 ++
> 5 files changed, 7 insertions(+)
> 
> diff --git a/Documentation/virt/kvm/api.txt b/Documentation/virt/kvm/api.txt
> index ebb37b34dcfc..6e5d92406b65 100644
> --- a/Documentation/virt/kvm/api.txt
> +++ b/Documentation/virt/kvm/api.txt
> @@ -4245,6 +4245,7 @@ hardware_exit_reason.
> 		/* KVM_EXIT_FAIL_ENTRY */
> 		struct {
> 			__u64 hardware_entry_failure_reason;
> +			__u32 cpu; /* if KVM_CAP_FAILED_ENTRY_CPU */
> 		} fail_entry;
> 
> If exit_reason is KVM_EXIT_FAIL_ENTRY, the vcpu could not be run due
> diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
> index 122d4ce3b1ab..4d06b2413c63 100644
> --- a/arch/x86/kvm/svm.c
> +++ b/arch/x86/kvm/svm.c
> @@ -4980,6 +4980,7 @@ static int handle_exit(struct kvm_vcpu *vcpu)
> 		kvm_run->exit_reason = KVM_EXIT_FAIL_ENTRY;
> 		kvm_run->fail_entry.hardware_entry_failure_reason
> 			= svm->vmcb->control.exit_code;
> +		kvm_run->fail_entry.cpu = raw_smp_processor_id();

Why not just use vcpu->cpu?
Same for vmx_handle_exit() to be consistent.

> 		dump_vmcb(vcpu);
> 		return 0;
> 	}
> diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
> index e3394c839dea..4d540b1c08e0 100644
> --- a/arch/x86/kvm/vmx/vmx.c
> +++ b/arch/x86/kvm/vmx/vmx.c
> @@ -5846,6 +5846,7 @@ static int vmx_handle_exit(struct kvm_vcpu *vcpu)
> 		vcpu->run->exit_reason = KVM_EXIT_FAIL_ENTRY;
> 		vcpu->run->fail_entry.hardware_entry_failure_reason
> 			= exit_reason;
> +		vcpu->run->fail_entry.cpu = vmx->loaded_vmcs->cpu;
> 		return 0;
> 	}
> 
> @@ -5854,6 +5855,7 @@ static int vmx_handle_exit(struct kvm_vcpu *vcpu)
> 		vcpu->run->exit_reason = KVM_EXIT_FAIL_ENTRY;
> 		vcpu->run->fail_entry.hardware_entry_failure_reason
> 			= vmcs_read32(VM_INSTRUCTION_ERROR);
> +		vcpu->run->fail_entry.cpu = vmx->loaded_vmcs->cpu;
> 		return 0;
> 	}
> 
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index cf917139de6b..9e89a32056d1 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -3273,6 +3273,7 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
> 	case KVM_CAP_GET_MSR_FEATURES:
> 	case KVM_CAP_MSR_PLATFORM_INFO:
> 	case KVM_CAP_EXCEPTION_PAYLOAD:
> +	case KVM_CAP_FAILED_ENTRY_CPU:
> 		r = 1;
> 		break;
> 	case KVM_CAP_SYNC_REGS:
> diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
> index f0a16b4adbbd..09ba7174456d 100644
> --- a/include/uapi/linux/kvm.h
> +++ b/include/uapi/linux/kvm.h
> @@ -277,6 +277,7 @@ struct kvm_run {
> 		/* KVM_EXIT_FAIL_ENTRY */
> 		struct {
> 			__u64 hardware_entry_failure_reason;
> +			__u32 cpu;
> 		} fail_entry;
> 		/* KVM_EXIT_EXCEPTION */
> 		struct {
> @@ -1009,6 +1010,7 @@ struct kvm_ppc_resize_hpt {
> #define KVM_CAP_PPC_GUEST_DEBUG_SSTEP 176
> #define KVM_CAP_ARM_NISV_TO_USER 177
> #define KVM_CAP_ARM_INJECT_EXT_DABT 178
> +#define KVM_CAP_FAILED_ENTRY_CPU 179
> 
> #ifdef KVM_CAP_IRQ_ROUTING
> 
> -- 
> 2.24.1.735.g03f4e72817-goog
> 





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