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LoongArch: KVM: Preserve memslot arch flags on KVM_MR_FLAGS_ONLY

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kvm_arch_prepare_memory_region() computes new->arch.flags, i.e. whether
a memslot is KVM_MEM_HUGEPAGE_CAPABLE or KVM_MEM_HUGEPAGE_INCAPABLE,
only for KVM_MR_CREATE and KVM_MR_MOVE, and returns early for every
other change. But the generic code allocates a zeroed memslot for every
change and never copies old->arch, so after a KVM_MR_FLAGS_ONLY update,
e.g. toggling KVM_MEM_LOG_DIRTY_PAGES for live migration, the active
memslot has arch.flags == 0.

With both flags clear, fault_supports_huge_mapping() falls through to
the alignment check on the HVA range alone, which no longer verifies
that the GPA and HVA have the same offset within a PMD. A memslot that
was marked KVM_MEM_HUGEPAGE_INCAPABLE because of a GPA/HVA offset
mismatch can then be mapped with PMD entries on read faults, and since
kvm_map_page() aligns the gfn and the pfn independently, the guest ends
up accessing the wrong host pages, exactly the "d -> f, e -> g" case
described in the comment above the check.

Carry the arch flags over from the old memslot for KVM_MR_FLAGS_ONLY,
as the GPA, HVA and size are guaranteed to be unchanged for that case.

Cc: stable@vger.kernel.org
Fixes: 7ab6fb505b ("LoongArch: KVM: Optimization for memslot hugepage checking")
Tested-by: Tao Cui <cuitao@kylinos.cn>
Reviewed-by: Tao Cui <cuitao@kylinos.cn>
Reviewed-by: Bibo Mao <maobibo@loongson.cn>
Signed-off-by: Zeng Chi <zengchi@kylinos.cn>
Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>
This commit is contained in:
Zeng Chi 2026-09-04 21:45:13 +08:00 committed by Huacai Chen
parent 40bdbb4bfa
commit 27a9bfee3b
1 changed files with 10 additions and 0 deletions
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10
arch/loongarch/kvm/mmu.c
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@ -383,6 +383,16 @@ int kvm_arch_prepare_memory_region(struct kvm *kvm, const struct kvm_memory_slot
hva_t hva_start;
size_t size, gpa_offset, hva_offset;
/*
* The generic code allocates a fresh, zeroed memslot for every change,
* so the arch flags computed below must be carried over when only the
* userspace flags change, e.g. when dirty logging is toggled.
*/
if (change == KVM_MR_FLAGS_ONLY) {
new->arch = old->arch;
return 0;
}
if ((change != KVM_MR_MOVE) && (change != KVM_MR_CREATE))
return 0;
/*