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

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Date:   Wed, 7 Jul 2021 23:20:04 +0000
From:   David Matlack <dmatlack@...gle.com>
To:     David Edmondson <david.edmondson@...cle.com>
Cc:     linux-kernel@...r.kernel.org, Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Borislav Petkov <bp@...en8.de>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Joerg Roedel <joro@...tes.org>, kvm@...r.kernel.org,
        Paolo Bonzini <pbonzini@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>, x86@...nel.org,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>
Subject: Re: [PATCH v2 0/2] kvm: x86: Convey the exit reason to user-space on
 emulation failure

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
>