Re: [RFC PATCH v5 27/29] KVM: selftests: Propagate KVM_EXIT_MEMORY_FAULT to userspace

[Chen, Zide]

On 12/12/2023 12:47 PM, Shashar, Sagi wrote:
> 
> 
> -----Original Message-----
> From: Sagi Shahar <sagis@xxxxxxxxxx> 
> Sent: Tuesday, December 12, 2023 12:47 PM
> To: linux-kselftest@xxxxxxxxxxxxxxx; Ackerley Tng <ackerleytng@xxxxxxxxxx>; Afranji, Ryan <afranji@xxxxxxxxxx>; Aktas, Erdem <erdemaktas@xxxxxxxxxx>; Sagi Shahar <sagis@xxxxxxxxxx>; Yamahata, Isaku <isaku.yamahata@xxxxxxxxx>
> Cc: Sean Christopherson <seanjc@xxxxxxxxxx>; Paolo Bonzini <pbonzini@xxxxxxxxxx>; Shuah Khan <shuah@xxxxxxxxxx>; Peter Gonda <pgonda@xxxxxxxxxx>; Xu, Haibo1 <haibo1.xu@xxxxxxxxx>; Chao Peng <chao.p.peng@xxxxxxxxxxxxxxx>; Annapurve, Vishal <vannapurve@xxxxxxxxxx>; Roger Wang <runanwang@xxxxxxxxxx>; Vipin Sharma <vipinsh@xxxxxxxxxx>; jmattson@xxxxxxxxxx; dmatlack@xxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx; kvm@xxxxxxxxxxxxxxx; linux-mm@xxxxxxxxx
> Subject: [RFC PATCH v5 27/29] KVM: selftests: Propagate KVM_EXIT_MEMORY_FAULT to userspace
> 
> Allow userspace to handle KVM_EXIT_MEMORY_FAULT instead of triggering TEST_ASSERT.
> 
> From the KVM_EXIT_MEMORY_FAULT documentation:
> Note!  KVM_EXIT_MEMORY_FAULT is unique among all KVM exit reasons in that it accompanies a return code of '-1', not '0'!  errno will always be set to EFAULT or EHWPOISON when KVM exits with KVM_EXIT_MEMORY_FAULT, userspace should assume kvm_run.exit_reason is stale/undefined for all other error numbers.

If KVM exits to userspace with KVM_EXIT_MEMORY_FAULT, most likely it's because the guest attempts to access the gfn in a way that is different from what the KVM is configured, in terms of private/shared property. I'd suggest to drop this patch and work on the selftests code to eliminate this exit.

If we need a testcase to catch this exit intentionally, we may call _vcpu_run() directly from the testcase and keep the common API vcpu_run() intact.

> 
> Signed-off-by: Sagi Shahar <sagis@xxxxxxxxxx>
> ---
>  tools/testing/selftests/kvm/lib/kvm_util.c | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/tools/testing/selftests/kvm/lib/kvm_util.c b/tools/testing/selftests/kvm/lib/kvm_util.c
> index d024abc5379c..8fb041e51484 100644
> --- a/tools/testing/selftests/kvm/lib/kvm_util.c
> +++ b/tools/testing/selftests/kvm/lib/kvm_util.c
> @@ -1742,6 +1742,10 @@ void vcpu_run(struct kvm_vcpu *vcpu)  {
>  	int ret = _vcpu_run(vcpu);
>  
> +	// Allow this scenario to be handled by the caller.
> +	if (ret == -1 && errno == EFAULT)
> +		return;
> +
>  	TEST_ASSERT(!ret, KVM_IOCTL_ERROR(KVM_RUN, ret));  }
>  
> --
> 2.43.0.472.g3155946c3a-goog
>