Re: [PATCH v2 0/2] kvm: x86: Convey the exit reason to user-space on emulation failure

From: David Matlack <dmatlack@google.com>
To: David Edmondson <david.edmondson@oracle.com>
Cc: linux-kernel@vger.kernel.org, Wanpeng Li <wanpengli@tencent.com>,
	Jim Mattson <jmattson@google.com>,
	Sean Christopherson <seanjc@google.com>,
	Borislav Petkov <bp@alien8.de>,
	Vitaly Kuznetsov <vkuznets@redhat.com>,
	Joerg Roedel <joro@8bytes.org>,
	kvm@vger.kernel.org, Paolo Bonzini <pbonzini@redhat.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	x86@kernel.org, Ingo Molnar <mingo@redhat.com>,
	"H. Peter Anvin" <hpa@zytor.com>
Subject: Re: [PATCH v2 0/2] kvm: x86: Convey the exit reason to user-space on emulation failure
Date: Wed, 7 Jul 2021 23:20:04 +0000	[thread overview]
Message-ID: <YOY2pLoXQ8ePXu0W@google.com> (raw)
In-Reply-To: <20210706101207.2993686-1-david.edmondson@oracle.com>

On Tue, Jul 06, 2021 at 11:12:05AM +0100, David Edmondson wrote:
> To help when debugging failures in the field, if instruction emulation
> fails, report the VM exit reason to userspace in order that it can be
> recorded.

What is the benefit of seeing the VM-exit reason that led to an
emulation failure?

> 
> I'm unsure whether sgx_handle_emulation_failure() needs to be adapted
> to use the emulation_failure part of the exit union in struct kvm_run
> - advice welcomed.
> 
> v2:
> - Improve patch comments (dmatlack)
> - Intel should provide the full exit reason (dmatlack)
> - Pass a boolean rather than flags (dmatlack)
> - Use the helper in kvm_task_switch() and kvm_handle_memory_failure()
>   (dmatlack)
> - Describe the exit_reason field of the emulation_failure structure
>   (dmatlack)
> 
> David Edmondson (2):
>   KVM: x86: Add kvm_x86_ops.get_exit_reason
>   KVM: x86: On emulation failure, convey the exit reason to userspace
> 
>  arch/x86/include/asm/kvm-x86-ops.h |  1 +
>  arch/x86/include/asm/kvm_host.h    |  3 +++
>  arch/x86/kvm/svm/svm.c             |  6 ++++++
>  arch/x86/kvm/vmx/vmx.c             | 11 +++++++----
>  arch/x86/kvm/x86.c                 | 22 +++++++++++++---------
>  include/uapi/linux/kvm.h           |  7 +++++++
>  6 files changed, 37 insertions(+), 13 deletions(-)
> 
> -- 
> 2.30.2
> 