Re: [PATCH v2 20/20] KVM: selftests: Add arch hook to force page tables to be naturally aligned

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [Medium] Using the ALIGN() macro with a potentially non-power-of-2 alignment value leads to incorrect alignment calculations and silent memory corruption.
--

commit ff7ec91da1b3e52d1f5f08d02d9a0f7729040242
Author: Sean Christopherson <seanjc@google.com>

KVM: selftests: Add arch hook to force page tables to be naturally aligned
    
Add an arch hook to communicate to the core physical page allocator that
page table allocations need to be naturally aligned. The hook will be used
for upcoming PowerPC support, which has MMU tables that are larger than the
guest base page size and need to be naturally aligned.

> diff --git a/tools/testing/selftests/kvm/lib/kvm_util.c b/tools/testing/selftests/kvm/lib/kvm_util.c
> index 8b5b330a58896..57b653fbd0b1f 100644
> --- a/tools/testing/selftests/kvm/lib/kvm_util.c
> +++ b/tools/testing/selftests/kvm/lib/kvm_util.c
[ ... ]
> @@ -2120,7 +2127,7 @@ gpa_t __vm_phy_pages_alloc(struct kvm_vm *vm, size_t nr_pages,
>  	}
>  
>  	return ____vm_phy_pages_alloc(vm, nr_pages, min_gpa, vm->memslots[type],
> -				      protected, false);
> +				      protected, naturally_aligned);

[Severity: Medium]
When naturally_aligned is true, ____vm_phy_pages_alloc() sets the alignment
to nr_pages:

	size_t alignment = naturally_aligned ? nr_pages : 1;
	...
	base = ALIGN(base, alignment);

Since ALIGN(x, a) mathematically requires the alignment 'a' to be a power
of 2, could this result in an incorrect base physical address calculation
if a caller requests a page table allocation with a non-power-of-2
nr_pages? This might silently fail to provide the requested alignment and
lead to overlapping allocations or hardware MMU faults.

>  }

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260902164123.2546762-1-seanjc@google.com?part=20