linux-kernel - [PATCH v2 32/32] KVM: selftests: Verify KVM disable interception (for userspace) on filter change

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Message-ID: <20250610225737.156318-33-seanjc@google.com>
Date: Tue, 10 Jun 2025 15:57:37 -0700
From: Sean Christopherson <seanjc@...gle.com>
To: Sean Christopherson <seanjc@...gle.com>, Paolo Bonzini <pbonzini@...hat.com>
Cc: kvm@...r.kernel.org, linux-kernel@...r.kernel.org, 
	Chao Gao <chao.gao@...el.com>, Borislav Petkov <bp@...en8.de>, Xin Li <xin@...or.com>, 
	Dapeng Mi <dapeng1.mi@...ux.intel.com>, Francesco Lavra <francescolavra.fl@...il.com>, 
	Manali Shukla <Manali.Shukla@....com>
Subject: [PATCH v2 32/32] KVM: selftests: Verify KVM disable interception (for
 userspace) on filter change

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.

Tested-by: Dapeng Mi <dapeng1.mi@...ux.intel.com>
Tested-by: Manali Shukla <Manali.Shukla@....com>
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);
 }
 
-- 
2.50.0.rc0.642.g800a2b2222-goog