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

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Date:   Thu, 08 Jul 2021 15:20:35 +0100
From:   David Edmondson <dme@....org>
To:     David Matlack <dmatlack@...gle.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 Wednesday, 2021-07-07 at 23:22:44 UTC, David Matlack wrote:

> 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.
>> 
>> 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)
>
> I just asked if Intel should provide the full exit reason, I do not have
> an opinion either way. It really comes down to your usecase for wanting
> the exit reason. Would the full exit reason be useful or do you just
> need the basic exit number?

Given that this is intended as a debug aid, having the full exit reason
makes sense.

>> - 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
>> 

dme.
-- 
You know it's not the twilight zone.