Re: [PATCH v2] KVM: arm64: Fix protected VM fault on system with pages larger than 4K

[Marc Zyngier <maz@kernel.org>]

On Mon, 14 Sep 2026 08:58:39 +0100,
Vincent Donnefort <vdonnefort@google.com> wrote:
> 
> Just like commit 08f97454b7fa ("KVM: arm64: Fix protected mode handling
> of pages larger than 4kB") fixed the boot of non-protected VMs on system
> larger than 4K pages, align the fault IPA down to the page-size for
> protected VMs.
> 
> To paraphrase Marc, pkvm_pgtable_stage2_map() assumes the address passed
> as a parameter is aligned to the size of the intended mapping, while
> HPFAR_EL2 gives the IPA minus the bottom 12 bits, regardless of the
> system page size configuration.
> 
> Add a check at the start of pkvm_pgtable_stage2_map() as we do not
> support !PAGE_ALIGNED arguments and use the gfn as an argument in all
> callers.
> 
> Fixes: ea03466e806f ("KVM: arm64: Handle aborts from protected VMs")
> Signed-off-by: Vincent Donnefort <vdonnefort@google.com>
> ---
> 
> Changelog:
> 
> v2:
>   - Use gfn_to_gpa(gfn)
>   - Drop "phys" from the PAGE_ALIGNED check, it isn't a requirement.
>   - Fix gmem_abort() as well (Sashiko)
> 
> v1: https://lore.kernel.org/all/20260913173516.3122436-1-vdonnefort@google.com/
> 
>  arch/arm64/kvm/mmu.c  | 7 ++++---
>  arch/arm64/kvm/pkvm.c | 3 +++
>  2 files changed, 7 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c
> index 9ba86450fe4a..ee78201a44df 100644
> --- a/arch/arm64/kvm/mmu.c
> +++ b/arch/arm64/kvm/mmu.c
> @@ -1672,10 +1672,10 @@ static int gmem_abort(const struct kvm_s2_fault_desc *s2fd)
>  		 * PTE, which will be preserved.
>  		 */

Context:

	if (s2fd->nested)
		gfn = kvm_s2_trans_output(s2fd->nested) >> PAGE_SHIFT;
	else
		gfn = s2fd->fault_ipa >> PAGE_SHIFT;

[...]

>  		prot &= ~KVM_NV_GUEST_MAP_SZ;
> -		ret = KVM_PGT_FN(kvm_pgtable_stage2_relax_perms)(pgt, s2fd->fault_ipa,
> +		ret = KVM_PGT_FN(kvm_pgtable_stage2_relax_perms)(pgt, gfn_to_gpa(gfn),
>  								 prot, flags);
>  	} else {
> -		ret = KVM_PGT_FN(kvm_pgtable_stage2_map)(pgt, s2fd->fault_ipa, PAGE_SIZE,
> +		ret = KVM_PGT_FN(kvm_pgtable_stage2_map)(pgt, gfn_to_gpa(gfn), PAGE_SIZE,
>  							 __pfn_to_phys(pfn), prot,
>  							 memcache, flags);

So 'gfn' is not related to the faulting IPA in the nested case, but is
the output address of the guest's own S2. You probably end-up with a
livelock handling the same fault forever, or worse.

It is a bit annoying that neither gmem nor pkvm are using
kvm_s2_fault_vma_info, which has the ability to reports all the
important stuff, as it would avoid this sort of bugs.

Thanks,

	M.

-- 
Without deviation from the norm, progress is not possible.