linux-kernel - Re: [PATCH 28/28] KVM: selftests: Verify KVM disable interception (for userspace) on filter change

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Message-ID: <c65b0cf9-a3cb-4e62-a40c-a69a14ea2255@amd.com>
Date: Wed, 4 Jun 2025 10:13:02 +0530
From: Manali Shukla <manali.shukla@....com>
To: Sean Christopherson <seanjc@...gle.com>,
 Paolo Bonzini <pbonzini@...hat.com>
Cc: kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
 Borislav Petkov <bp@...en8.de>, Xin Li <xin@...or.com>,
 Chao Gao <chao.gao@...el.com>, "Mi, Dapeng" <dapeng1.mi@...ux.intel.com>
Subject: Re: [PATCH 28/28] KVM: selftests: Verify KVM disable interception
 (for userspace) on filter change

On 6/3/2025 11:17 AM, Mi, Dapeng wrote:
> 
> On 5/30/2025 7:40 AM, Sean Christopherson wrote:
>> Re-read MSR_{FS,GS}_BASE after restoring the "allow everything" userspace
>> MSR filter to verify that KVM stops forwarding exits to userspace.  This
>> can also be used in conjunction with manual verification (e.g. printk) to
>> ensure KVM is correctly updating the MSR bitmaps consumed by hardware.
>>
>> Signed-off-by: Sean Christopherson <seanjc@...gle.com>
>> ---
>>  tools/testing/selftests/kvm/x86/userspace_msr_exit_test.c | 8 ++++++++
>>  1 file changed, 8 insertions(+)
>>
>> diff --git a/tools/testing/selftests/kvm/x86/userspace_msr_exit_test.c b/tools/testing/selftests/kvm/x86/userspace_msr_exit_test.c
>> index 32b2794b78fe..8463a9956410 100644
>> --- a/tools/testing/selftests/kvm/x86/userspace_msr_exit_test.c
>> +++ b/tools/testing/selftests/kvm/x86/userspace_msr_exit_test.c
>> @@ -343,6 +343,12 @@ static void guest_code_permission_bitmap(void)
>>  	data = test_rdmsr(MSR_GS_BASE);
>>  	GUEST_ASSERT(data == MSR_GS_BASE);
>>  
>> +	/* Access the MSRs again to ensure KVM has disabled interception.*/
>> +	data = test_rdmsr(MSR_FS_BASE);
>> +	GUEST_ASSERT(data != MSR_FS_BASE);
>> +	data = test_rdmsr(MSR_GS_BASE);
>> +	GUEST_ASSERT(data != MSR_GS_BASE);
>> +
>>  	GUEST_DONE();
>>  }
>>  
>> @@ -682,6 +688,8 @@ KVM_ONE_VCPU_TEST(user_msr, msr_permission_bitmap, guest_code_permission_bitmap)
>>  		    "Expected ucall state to be UCALL_SYNC.");
>>  	vm_ioctl(vm, KVM_X86_SET_MSR_FILTER, &filter_gs);
>>  	run_guest_then_process_rdmsr(vcpu, MSR_GS_BASE);
>> +
>> +	vm_ioctl(vm, KVM_X86_SET_MSR_FILTER, &filter_allow);
>>  	run_guest_then_process_ucall_done(vcpu);
>>  }
>>  
> 
> Test passes on Intel platform (Sapphire Rapids).
> 
> Tested-by: Dapeng Mi <dapeng1.mi@...ux.intel.com>
> 
> 

This test passes on AMD platform (Genoa)

Tested-by: Manali Shukla <Manali.Shukla@....com>