Re: [PATCH v2 06/20] KVM: selftests: Extend page allocator to support naturally aligned allocations

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [Medium] The `ALIGN()` macro is used with `nr_pages` as the alignment constraint, but there is no validation to ensure `nr_pages` is a power of two, which `ALIGN()` strictly requires.
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commit 1b8052ce0034b1eff1950b660c7716fd2dffde7a
Author: Sean Christopherson <seanjc@google.com>

KVM: selftests: Extend page allocator to support naturally aligned allocations

This commit extends the KVM selftests page allocator to support naturally
aligned allocations. This is primarily for some flavors of PowerPC page tables
that require multiple guest pages per table, and those tables 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 bbf6d7684c0ca..896da440659e3 100644
> --- a/tools/testing/selftests/kvm/lib/kvm_util.c
> +++ b/tools/testing/selftests/kvm/lib/kvm_util.c
[ ... ]
> @@ -2032,9 +2033,10 @@ const char *exit_reason_str(unsigned int exit_reason)
>   *
>   * Note, success is guaranteed!
>   */
> -gpa_t __vm_phy_pages_alloc(struct kvm_vm *vm, size_t nr_pages, gpa_t min_gpa,
> -			   u32 memslot, bool protected)
> +gpa_t ____vm_phy_pages_alloc(struct kvm_vm *vm, size_t nr_pages, gpa_t min_gpa,
> +			     u32 memslot, bool protected, bool naturally_aligned)
>  {
> +	size_t alignment = naturally_aligned ? nr_pages : 1;
>  	struct userspace_mem_region *region;
>  	sparsebit_idx_t pg, base;
>  
[ ... ]
> @@ -2051,6 +2053,7 @@ gpa_t __vm_phy_pages_alloc(struct kvm_vm *vm, size_t nr_pages, gpa_t min_gpa,
>  
>  	base = min_gpa >> vm->page_shift;
>  again:
> +	base = ALIGN(base, alignment);

[Severity: Medium]
Are there any scenarios where ____vm_phy_pages_alloc() is called with
naturally_aligned set to true but nr_pages is not a power of two?

The ALIGN() macro uses bitwise arithmetic and mathematically requires the
alignment constraint to be a power of two. If nr_pages is not a power of
two, ALIGN() will silently compute an incorrect base address.

Would it be safer to add a check to ensure nr_pages is a power of two when
naturally_aligned is requested?

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Sashiko AI review · https://sashiko.dev/#/patchset/20260902164123.2546762-1-seanjc@google.com?part=6