[PATCH] KVM: x86/mmu: Fix NX page unaccounting for TDP MMU pages

[PATCH] KVM: x86/mmu: Fix NX page unaccounting for TDP MMU pages

[Carlos López]

unaccount_nx_huge_page() unconditionally passes KVM_SHADOW_MMU to
untrack_possible_nx_huge_page(), which is incorrect, particularly on
the path from kvm_recover_nx_huge_pages(), which handles pages from
both MMUs. Fix this by retrieving the MMU type via is_tdp_mmu_page()
and passing it down.

Fixes: 6777885605e1 ("KVM: x86/mmu: Track possible NX huge pages separately for TDP vs. Shadow MMU")
Signed-off-by: Carlos López <clopez@suse.de>
---
 arch/x86/kvm/mmu/mmu.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index 9788ff180374..61996669b6f6 100644
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -866,9 +866,11 @@ void untrack_possible_nx_huge_page(struct kvm *kvm, struct kvm_mmu_page *sp,
 
 static void unaccount_nx_huge_page(struct kvm *kvm, struct kvm_mmu_page *sp)
 {
+	enum kvm_mmu_type mmu_type = is_tdp_mmu_page(sp) ? KVM_TDP_MMU : KVM_SHADOW_MMU;
+
 	sp->nx_huge_page_disallowed = false;
 
-	untrack_possible_nx_huge_page(kvm, sp, KVM_SHADOW_MMU);
+	untrack_possible_nx_huge_page(kvm, sp, mmu_type);
 }
 
 static struct kvm_memory_slot *gfn_to_memslot_dirty_bitmap(struct kvm_vcpu *vcpu,

base-commit: 70c944caf570fda2d79baa71435589a8db39f048
-- 
2.51.0

Re: [PATCH] KVM: x86/mmu: Fix NX page unaccounting for TDP MMU pages

[sashiko-bot]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [Low] mmu: build failure on 32-bit x86 due to undeclared KVM_TDP_MMU
--

commit c2443a58667359b4d898625aee21d7fa954accfd
Author: Carlos López <clopez@suse.de>
KVM: x86/mmu: Fix NX page unaccounting for TDP MMU pages

This commit fixes unaccounting of NX huge pages for TDP MMU pages by passing
the correct MMU type to untrack_possible_nx_huge_page() instead of always
hardcoding KVM_SHADOW_MMU.

> diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
> index 9788ff1803740..61996669b6f6a 100644
> --- a/arch/x86/kvm/mmu/mmu.c
> +++ b/arch/x86/kvm/mmu/mmu.c
[ ... ]
> @@ -866,9 +866,11 @@ void untrack_possible_nx_huge_page(struct kvm *kvm, struct kvm_mmu_page *sp,
>  
>  static void unaccount_nx_huge_page(struct kvm *kvm, struct kvm_mmu_page *sp)
>  {
> +	enum kvm_mmu_type mmu_type = is_tdp_mmu_page(sp) ? KVM_TDP_MMU : KVM_SHADOW_MMU;

[Severity: Low]
Will this break the build on 32-bit x86 systems? KVM_TDP_MMU is only defined 
when CONFIG_X86_64 is enabled. Unconditionally referencing it here in 
unaccount_nx_huge_page() will result in an undeclared identifier error when 
compiling KVM with CONFIG_X86_32=y.

> +
>  	sp->nx_huge_page_disallowed = false;
>  
> -	untrack_possible_nx_huge_page(kvm, sp, KVM_SHADOW_MMU);
> +	untrack_possible_nx_huge_page(kvm, sp, mmu_type);
>  }

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260915203511.1808028-1-clopez@suse.de?part=1