Re: [PATCH v2 2/2] KVM: selftests: Add a hugetlb memslot alignment test mode

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [Medium] Moving the memslot GPA by `guest_page_size` breaks KVM's host page size alignment requirement when `guest_page_size < host_page_size`.
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commit 6f87612dbda5d8765dabde103b78b45366d2e3b8
Author: Jinyu Tang <tjytimi@163.com>

KVM: selftests: Add a hugetlb memslot alignment test mode

This commit adds a -u option to kvm_page_table_test to intentionally
misalign the test memslot GPA by one guest page. It creates the memslot
aligned and then moves it to create a deliberate HVA/GPA offset mismatch.

> diff --git a/tools/testing/selftests/kvm/kvm_page_table_test.c b/tools/testing/selftests/kvm/kvm_page_table_test.c
> index fc5242fb956fc..a910e3abb8c71 100644
> --- a/tools/testing/selftests/kvm/kvm_page_table_test.c
> +++ b/tools/testing/selftests/kvm/kvm_page_table_test.c
[ ... ]
> @@ -276,13 +278,22 @@ static struct kvm_vm *pre_init_before_test(enum vm_guest_mode mode, void *arg)
>  	/* Add an extra memory slot with specified backing src type */
>  	vm_userspace_mem_region_add(vm, src_type, guest_test_phys_mem,
>  				    TEST_MEM_SLOT_INDEX, guest_num_pages, 0);
> +	region = memslot2region(vm, TEST_MEM_SLOT_INDEX);
> +	host_test_mem = region->host_mem;
> +
> +	if (p->misalign_slot_gpa) {
> +		TEST_ASSERT(is_backing_src_hugetlb(src_type),
> +			    "Memslot GPA misalignment requires hugetlb backing");
> +		TEST_ASSERT(guest_num_pages > 1,
> +			    "Need at least two guest pages to misalign memslot GPA");
> +
> +		guest_test_phys_mem += guest_page_size;
> +		vm_mem_region_move(vm, TEST_MEM_SLOT_INDEX, guest_test_phys_mem);

[Severity: Medium]
Will this move operation fail on hosts where the guest page size is smaller
than the host page size?

The KVM_SET_USER_MEMORY_REGION ioctl requires the guest physical address to
be aligned to the host's page size. 

Because for_each_guest_mode() iterates through configurations that can have a
smaller guest page size (like a 4K guest on a 64K ARM64 host), adding
guest_page_size to the aligned GPA will produce a misaligned address for KVM.

Could vm_mem_region_move() fail with -EINVAL from KVM in these cases, causing
the test assertion to fail? Would it be safer to shift by the maximum of the
guest page size and the host page size?

> +	}
>  
>  	/* Do mapping(GVA->GPA) for the testing memory slot */
>  	virt_map(vm, guest_test_virt_mem, guest_test_phys_mem, guest_num_pages);

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Sashiko AI review · https://sashiko.dev/#/patchset/20260604142602.3582602-1-tjytimi@163.com?part=2