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

[Mi, Dapeng]

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@xxxxxxxxxx>
> ---
>  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@xxxxxxxxxxxxxxx>