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Date: Thu, 14 Mar 2024 14:46:38 -0700
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Subject: Re: [RFC PATCH v5 27/29] KVM: selftests: Propagate
 KVM_EXIT_MEMORY_FAULT to userspace
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To: Sagi Shahar <sagis@google.com>, linux-kselftest@vger.kernel.org,
 Ackerley Tng <ackerleytng@google.com>, "Afranji, Ryan" <afranji@google.com>,
 "Aktas, Erdem" <erdemaktas@google.com>, Sagi Shahar <sagis@google.com>,
 "Yamahata, Isaku" <isaku.yamahata@intel.com>
References: <20231212204647.2170650-1-sagis@google.com>
 <20231212204647.2170650-28-sagis@google.com>
 <DS7PR11MB78860170A5FD77253573BC09F6292@DS7PR11MB7886.namprd11.prod.outlook.com>
Cc: Sean Christopherson <seanjc@google.com>,
 Paolo Bonzini <pbonzini@redhat.com>, Shuah Khan <shuah@kernel.org>,
 Peter Gonda <pgonda@google.com>, "Xu, Haibo1" <haibo1.xu@intel.com>,
 Chao Peng <chao.p.peng@linux.intel.com>,
 "Annapurve, Vishal" <vannapurve@google.com>,
 Roger Wang <runanwang@google.com>, Vipin Sharma <vipinsh@google.com>,
 jmattson@google.com, dmatlack@google.com, linux-kernel@vger.kernel.org,
 kvm@vger.kernel.org, linux-mm@kvack.org
From: "Chen, Zide" <zide.chen@intel.com>
In-Reply-To: <DS7PR11MB78860170A5FD77253573BC09F6292@DS7PR11MB7886.namprd11.prod.outlook.com>
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On 12/12/2023 12:47 PM, Shashar, Sagi wrote:
> 
> 
> -----Original Message-----
> From: Sagi Shahar <sagis@google.com> 
> Sent: Tuesday, December 12, 2023 12:47 PM
> To: linux-kselftest@vger.kernel.org; Ackerley Tng <ackerleytng@google.com>; Afranji, Ryan <afranji@google.com>; Aktas, Erdem <erdemaktas@google.com>; Sagi Shahar <sagis@google.com>; Yamahata, Isaku <isaku.yamahata@intel.com>
> Cc: Sean Christopherson <seanjc@google.com>; Paolo Bonzini <pbonzini@redhat.com>; Shuah Khan <shuah@kernel.org>; Peter Gonda <pgonda@google.com>; Xu, Haibo1 <haibo1.xu@intel.com>; Chao Peng <chao.p.peng@linux.intel.com>; Annapurve, Vishal <vannapurve@google.com>; Roger Wang <runanwang@google.com>; Vipin Sharma <vipinsh@google.com>; jmattson@google.com; dmatlack@google.com; linux-kernel@vger.kernel.org; kvm@vger.kernel.org; linux-mm@kvack.org
> 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@google.com>
> ---
>  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
>