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Mon, 04 May 2026 15:42:35 -0700 (PDT) Date: Mon, 4 May 2026 22:42:08 +0000 In-Reply-To: <20260504224213.1049426-1-jthoughton@google.com> Mime-Version: 1.0 References: <20260504224213.1049426-1-jthoughton@google.com> X-Mailer: git-send-email 2.54.0.545.g6539524ca2-goog Message-ID: <20260504224213.1049426-2-jthoughton@google.com> Subject: [PATCH 1/5] KVM: arm64: Grab KVM MMU write lock in kvm_arch_flush_shadow_all() From: James Houghton To: Paolo Bonzini Cc: Marc Zyngier , Oliver Upton , Joey Gouly , Suzuki K Poulose , Zenghui Yu , Sean Christopherson , Gavin Shan , Shaoqin Huang , Ricardo Koller , Tianrui Zhao , Bibo Mao , Huacai Chen , James Hogan , linux-arm-kernel@lists.infradead.org, kvmarm@lists.linux.dev, loongarch@lists.linux.dev, linux-mips@vger.kernel.org, kvm@vger.kernel.org, linux-kernel@vger.kernel.org, James Houghton , stable@vger.kernel.org Content-Type: text/plain; charset="UTF-8" X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20260504_154237_932594_84534A2B X-CRM114-Status: GOOD ( 16.42 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org kvm_arch_flush_shadow_all() may sometimes be called on the same `kvm` concurrently in the event that the KVM's `mm` is __mmput() at the same time that last reference to the KVM is being dropped. T1 T2 KVM_CREATE_VM Get VM file from T1 close VM exit_mm() close VM T1: exit_mm() -> kvm_mmu_notifier_release() -> kvm_flush_shadow_all(), with only the KVM srcu read lock held. T2: kvm_vm_release() ---> mmu_notifier_unregister() -> kvm_mmu_notifier_release() -> kvm_flush_shadow_all(), again, with only the KVM srcu read lock held. This leads to a potential double-free of kvm->arch.kvm_mmu_free_memory_cache and now with NV kvm->arch.nested_mmus. Cc: stable@vger.kernel.org Fixes: e7bf7a490c68 ("KVM: arm64: Split huge pages when dirty logging is enabled") Signed-off-by: James Houghton --- arch/arm64/include/asm/kvm_mmu.h | 1 + arch/arm64/kvm/mmu.c | 23 +++++++++++++++++++---- arch/arm64/kvm/nested.c | 4 +++- 3 files changed, 23 insertions(+), 5 deletions(-) diff --git a/arch/arm64/include/asm/kvm_mmu.h b/arch/arm64/include/asm/kvm_mmu.h index 01e9c72d6aa7..30d5c24fcebb 100644 --- a/arch/arm64/include/asm/kvm_mmu.h +++ b/arch/arm64/include/asm/kvm_mmu.h @@ -178,6 +178,7 @@ void stage2_unmap_vm(struct kvm *kvm); int kvm_init_stage2_mmu(struct kvm *kvm, struct kvm_s2_mmu *mmu, unsigned long type); void kvm_uninit_stage2_mmu(struct kvm *kvm); void kvm_free_stage2_pgd(struct kvm_s2_mmu *mmu); +void kvm_free_stage2_pgd_locked(struct kvm_s2_mmu *mmu); int kvm_phys_addr_ioremap(struct kvm *kvm, phys_addr_t guest_ipa, phys_addr_t pa, unsigned long size, bool writable); diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c index d089c107d9b7..4bab407d43bb 100644 --- a/arch/arm64/kvm/mmu.c +++ b/arch/arm64/kvm/mmu.c @@ -1021,7 +1021,9 @@ int kvm_init_stage2_mmu(struct kvm *kvm, struct kvm_s2_mmu *mmu, unsigned long t void kvm_uninit_stage2_mmu(struct kvm *kvm) { - kvm_free_stage2_pgd(&kvm->arch.mmu); + lockdep_assert_held_write(&kvm->mmu_lock); + + kvm_free_stage2_pgd_locked(&kvm->arch.mmu); kvm_mmu_free_memory_cache(&kvm->arch.mmu.split_page_cache); } @@ -1095,12 +1097,14 @@ void stage2_unmap_vm(struct kvm *kvm) srcu_read_unlock(&kvm->srcu, idx); } -void kvm_free_stage2_pgd(struct kvm_s2_mmu *mmu) +static void __kvm_free_stage2_pgd(struct kvm_s2_mmu *mmu, bool locked) { struct kvm *kvm = kvm_s2_mmu_to_kvm(mmu); struct kvm_pgtable *pgt = NULL; - write_lock(&kvm->mmu_lock); + if (!locked) + write_lock(&kvm->mmu_lock); + pgt = mmu->pgt; if (pgt) { mmu->pgd_phys = 0; @@ -1111,7 +1115,8 @@ void kvm_free_stage2_pgd(struct kvm_s2_mmu *mmu) if (kvm_is_nested_s2_mmu(kvm, mmu)) kvm_init_nested_s2_mmu(mmu); - write_unlock(&kvm->mmu_lock); + if (!locked) + write_unlock(&kvm->mmu_lock); if (pgt) { kvm_stage2_destroy(pgt); @@ -1119,6 +1124,16 @@ void kvm_free_stage2_pgd(struct kvm_s2_mmu *mmu) } } +void kvm_free_stage2_pgd(struct kvm_s2_mmu *mmu) +{ + __kvm_free_stage2_pgd(mmu, false); +} + +void kvm_free_stage2_pgd_locked(struct kvm_s2_mmu *mmu) +{ + __kvm_free_stage2_pgd(mmu, true); +} + static void hyp_mc_free_fn(void *addr, void *mc) { struct kvm_hyp_memcache *memcache = mc; diff --git a/arch/arm64/kvm/nested.c b/arch/arm64/kvm/nested.c index 883b6c1008fb..977598bff5e6 100644 --- a/arch/arm64/kvm/nested.c +++ b/arch/arm64/kvm/nested.c @@ -1190,11 +1190,13 @@ void kvm_arch_flush_shadow_all(struct kvm *kvm) { int i; + guard(write_lock)(&kvm->mmu_lock); + for (i = 0; i < kvm->arch.nested_mmus_size; i++) { struct kvm_s2_mmu *mmu = &kvm->arch.nested_mmus[i]; if (!WARN_ON(atomic_read(&mmu->refcnt))) - kvm_free_stage2_pgd(mmu); + kvm_free_stage2_pgd_locked(mmu); } kvfree(kvm->arch.nested_mmus); kvm->arch.nested_mmus = NULL; -- 2.54.0.545.g6539524ca2-goog