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Tue, 21 Jul 2026 03:35:38 -0700 (PDT) From: Jinu Kim To: Sean Christopherson Cc: Paolo Bonzini , kvm@vger.kernel.org, linux-kernel@vger.kernel.org Subject: [PATCH v2 2/2] KVM: x86/mmu: Check all address spaces before skipping unsync Date: Tue, 21 Jul 2026 19:35:12 +0900 Message-ID: <20260721103512.2136240-3-kimjw04271234@gmail.com> X-Mailer: git-send-email 2.43.0 In-Reply-To: <20260721103512.2136240-1-kimjw04271234@gmail.com> References: <20260721103512.2136240-1-kimjw04271234@gmail.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit mmu_try_to_unsync_pages() skips the shadow-page lookup when the supplied memslot allows a hugepage, because a shadow page would disallow hugepages. But hugepage metadata is per-address-space while shadow pages are shared across all address spaces. With SMM, the other address space can therefore have a shadow page even when the supplied memslot allows a hugepage. Check the corresponding memslot in the other address space before taking the fast path. Skip the shadow-page lookup only when all address spaces allow a hugepage. Fixes: b3ae3ceb5569 ("KVM: x86/mmu: KVM: x86/mmu: Skip unsync when large pages are allowed") Assisted-by: Codex:GPT-5 Signed-off-by: Jinu Kim --- arch/x86/kvm/mmu/mmu.c | 21 ++++++++++++++++++++- 1 file changed, 20 insertions(+), 1 deletion(-) diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c index 7757f0ad65c6f..1db6750992546 100644 --- a/arch/x86/kvm/mmu/mmu.c +++ b/arch/x86/kvm/mmu/mmu.c @@ -725,6 +725,25 @@ static struct kvm_lpage_info *lpage_info_slot(gfn_t gfn, return &slot->arch.lpage_info[level - 2][idx]; } +static bool kvm_gfn_is_lpage_allowed(struct kvm *kvm, + const struct kvm_memory_slot *slot, + gfn_t gfn, int level) +{ + const struct kvm_memory_slot *other_slot; + + BUILD_BUG_ON(KVM_MAX_NR_ADDRESS_SPACES > 2); + + if (lpage_info_slot(gfn, slot, level)->disallow_lpage) + return false; + + if (kvm_arch_nr_memslot_as_ids(kvm) == 1) + return true; + + other_slot = __gfn_to_memslot(__kvm_memslots(kvm, slot->as_id ^ 1), gfn); + return !other_slot || + !lpage_info_slot(gfn, other_slot, level)->disallow_lpage; +} + /* * The most significant bit in disallow_lpage tracks whether or not memory * attributes are mixed, i.e. not identical for all gfns at the current level. @@ -2972,7 +2991,7 @@ int mmu_try_to_unsync_pages(struct kvm *kvm, const struct kvm_memory_slot *slot, * write-protected (see above), thus if the gfn can be mapped with a * hugepage and isn't write-tracked, it can't have a shadow page. */ - if (!lpage_info_slot(gfn, slot, PG_LEVEL_2M)->disallow_lpage) + if (kvm_gfn_is_lpage_allowed(kvm, slot, gfn, PG_LEVEL_2M)) return 0; /* -- 2.43.0