Re: [PATCH 2/2] KVM: selftests: Test that KVM_RUN fails for unresolvable host faults

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [Medium] KVM: selftests: missing gmem_flags argument to vm_mem_add() in main()
--

commit 3a1c0f90404979b6638dbd3c2769d7b78633b104
Author: Christian Borntraeger <borntraeger@linux.ibm.com>

KVM: selftests: Test that KVM_RUN fails for unresolvable host faults

This commit adds a selftest in which a guest writes to a shmem-backed
memslot beyond the end of the file to verify that KVM_RUN fails with
-EFAULT rather than retrying an asynchronous page fault indefinitely.

> diff --git a/tools/testing/selftests/kvm/faultin_sigbus_test.c b/tools/testing/selftests/kvm/faultin_sigbus_test.c
> new file mode 100644
> index 0000000000000..b9d673260ed5a
> --- /dev/null
> +++ b/tools/testing/selftests/kvm/faultin_sigbus_test.c
> @@ -0,0 +1,168 @@

[ ... ]

> +int main(void)
> +{
> +	struct sigaction sa = { .sa_handler = sig_alarm };	/* no SA_RESTART */
> +	struct userspace_mem_region *region;
> +	struct kvm_vcpu *vcpu;
> +	struct kvm_vm *vm;
> +	struct ucall uc;
> +	gpa_t gpa;
> +	gva_t gva;
> +	u64 npages;
> +	int r;
> +
> +	vm = vm_create_with_one_vcpu(&vcpu, guest_code);
> +
> +	/* After slot 0 and the page that some architectures use for ucalls. */
> +	region = memslot2region(vm, 0);
> +	gpa = align_up(region->region.guest_phys_addr +
> +		       region->region.memory_size + vm->page_size, TEST_SIZE);
> +	npages = TEST_SIZE / vm->page_size;
> +
> +	vm_mem_add(vm, VM_MEM_SRC_SHMEM, gpa, TEST_SLOT, npages, 0, -1, 0);

[Severity: Medium]
Does this fail to build when compiling KVM selftests?

In tools/testing/selftests/kvm/include/kvm_util.h (and
tools/testing/selftests/kvm/lib/kvm_util.c), vm_mem_add() takes 9
arguments following commit ee455183c92be7:

void vm_mem_add(struct kvm_vm *vm, enum vm_mem_backing_src_type src_type,
		gpa_t gpa, u32 slot, u64 npages, u32 flags,
		int gmem_fd, u64 gmem_offset, u64 gmem_flags);

Calling vm_mem_add() in main() with only 8 arguments omits the final
gmem_flags parameter and fails compilation with too few arguments to
function vm_mem_add. Should this pass the 9th argument (0), or use the
6-argument helper vm_userspace_mem_region_add(vm, VM_MEM_SRC_SHMEM, gpa,
TEST_SLOT, npages, 0) instead?

> +	region = memslot2region(vm, TEST_SLOT);
> +	/* Only the first host page is backed, everything behind it is SIGBUS. */
> +	TEST_ASSERT(!ftruncate(region->fd, getpagesize()), "ftruncate() failed");

[ ... ]

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20261020143308.228328-1-borntraeger@linux.ibm.com?part=2