Re: [PATCH 09/45] KVM: Define and communicate KVM_EXIT_MEMORY_FAULT RWX flags to userspace

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [Medium] KVM: flag change in kvm_prepare_memory_fault_exit() breaks selftest
--

commit 97c15077daea43ee7bc4ecb13d9cec2a636fe69e
Author: Anish Moorthy <amoorthy@google.com>

KVM: Define and communicate KVM_EXIT_MEMORY_FAULT RWX flags to userspace

This commit defines KVM_MEMORY_EXIT_FLAG_READ, KVM_MEMORY_EXIT_FLAG_WRITE,
and KVM_MEMORY_EXIT_FLAG_EXEC in the UAPI header and updates
kvm_prepare_memory_fault_exit() to populate vcpu->run->memory_fault.flags
with the corresponding access type flag.

Link: https://lore.kernel.org/kvm/ZR4N8cwzTMDanPUY@google.com/
Link: https://patch.msgid.link/20260918135030.171564-4-pbonzini@redhat.com

> diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
> index e7fc94e2910a8..5e386c3d24957 100644
> --- a/include/linux/kvm_host.h
> +++ b/include/linux/kvm_host.h
> @@ -2556,8 +2556,15 @@ static inline void kvm_prepare_memory_fault_exit(struct kvm_vcpu *vcpu,
>  	vcpu->run->memory_fault.gpa = gpa;
>  	vcpu->run->memory_fault.size = size;
>  
> -	/* RWX flags are not (yet) defined or communicated to userspace. */
>  	vcpu->run->memory_fault.flags = 0;
> +
> +	if (is_write)
> +		vcpu->run->memory_fault.flags |= KVM_MEMORY_EXIT_FLAG_WRITE;
> +	else if (is_exec)
> +		vcpu->run->memory_fault.flags |= KVM_MEMORY_EXIT_FLAG_EXEC;
> +	else
> +		vcpu->run->memory_fault.flags |= KVM_MEMORY_EXIT_FLAG_READ;

[Severity: Medium]
Does setting KVM_MEMORY_EXIT_FLAG_READ here break
test_private_access_memslot_deleted() in
tools/testing/selftests/kvm/x86/private_mem_kvm_exits_test.c when
!kvm_has_gmem_attributes?

In that test, the vCPU runs guest_repeatedly_read() on private guest memory
while the backing memslot is deleted, causing kvm_handle_noslot_fault() ->
kvm_mmu_prepare_memory_fault_exit() -> kvm_prepare_memory_fault_exit() to set
vcpu->run->memory_fault.flags to KVM_MEMORY_EXIT_FLAG_PRIVATE |
KVM_MEMORY_EXIT_FLAG_READ.

Earlier commit 628770546898 ("KVM: selftests: Take into account mixed memory
fault flags") added a bitwise check in test_private_access_memslot_deleted(),
but left the exact equality assertion in place right above it:

tools/testing/selftests/kvm/x86/private_mem_kvm_exits_test.c:test_private_access_memslot_deleted() {
	...
	} else {
		TEST_ASSERT_EQ(exit_reason, KVM_EXIT_MEMORY_FAULT);
		TEST_ASSERT_EQ(vcpu->run->memory_fault.flags, KVM_MEMORY_EXIT_FLAG_PRIVATE);
		TEST_ASSERT(vcpu->run->memory_fault.flags & KVM_MEMORY_EXIT_FLAG_PRIVATE,
			    "Memory fault didn't occur on a private memory access");
		TEST_ASSERT_EQ(vcpu->run->memory_fault.gpa, EXITS_TEST_GPA);
		TEST_ASSERT_EQ(vcpu->run->memory_fault.size, EXITS_TEST_SIZE);
	}
	...
}

Should that leftover TEST_ASSERT_EQ(vcpu->run->memory_fault.flags,
KVM_MEMORY_EXIT_FLAG_PRIVATE) be removed so the selftest does not fail once
KVM_MEMORY_EXIT_FLAG_READ is set?

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20261102174130.8779-1-pbonzini@redhat.com?part=9