From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 62A37440A13; Mon, 17 Aug 2026 15:17:51 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1786979872; cv=none; b=MB3n4OtVRTmFG3HhHGmQJdtO+YXpOGAtPB/CfxdhfBNX337TjH6lCqeNpf/MBybaXjJio7fEaCqjODYj5C6tD/zCFfdlmCd8OxC8TrRzEaggDOVoM6xxfQzKOk3i1tG9r7CTCOOS0dbSDan1GTuIXDQ3LzpEt6TR5kOlQTvLpD8= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1786979872; c=relaxed/simple; bh=e3BUskELDxzWsNaOkWVl9/P3X8lKT1YXroISrA+LOms=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=IJ3V8vg2Wz6qxdQGs2JGBg69DXljo79QEgxGv4hrKymxXxgUNbSUFvkRV8/4XkSrUuVYXnzaM20R+AR725YzoBNumLE8OFHXBpidF6xQpE2dAayj4HWaBsdVKVXwhDo8lomlx1pkaRUYR6KBlgMNoxAnrTZ4b/B5iFfEzGTzSo8= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=cZ9lgMsH; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="cZ9lgMsH" Received: by smtp.kernel.org (Postfix) with ESMTPSA id DFD1B1F00A3A; Mon, 17 Aug 2026 15:17:48 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1786979871; bh=ss7U/2YTy9A3C2Z/p5RynpbaJ0lWEE5CiNvY0Z+Tm0c=; h=Date:From:To:Cc:Subject:References:In-Reply-To; b=cZ9lgMsH0gcoBRT6droiOSss6vTfVMkynwppmaixyAeQbiHrChEVYwLx6zbdsnvUU 1yzab0a1foS+QPnbxd3PaHMVQXk+tSp5x7Rc7oXKkW1zwBtMQ4MWuS1Hv8GXP+7YWc 5tPa4N8MK5peK7eXOooRYnCgWBodRnwDkVcwRXDmy1N9fnPW6dKTrc6JamxcalIHxG cYcc581bTE458B0CLv8nuY2+I95Wj1B3gcEYTXHbgeCo1WjfXmvIweuCORA/Yo4V2L jFDnNcJdTGeWQpSCexKo4W6vGD5mePjsfbB9wYRxh6hN423MIPE8P+/A52DrFkauSC oQokxOfT52wCA== Date: Mon, 17 Aug 2026 16:17:46 +0100 From: "Lorenzo Stoakes (ARM)" To: Marc Zyngier Cc: kvmarm@lists.linux.dev, linux-arm-kernel@lists.infradead.org, Steffen Eiden , Joey Gouly , Suzuki K Poulose , Oliver Upton , Zenghui Yu , Fuad Tabba , Shen Yongchao , Karl Mehltretter , Wei-Lin Chang , stable@vger.kernel.org Subject: Re: [PATCH v2 1/2] KVM: arm64: nv: Fix life cycle of the nested_mmus array Message-ID: References: <20260814103230.858578-1-maz@kernel.org> <20260814103230.858578-2-maz@kernel.org> Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260814103230.858578-2-maz@kernel.org> On Fri, Aug 14, 2026 at 11:32:29AM +0100, Marc Zyngier wrote: > The nested_mmus array holds the shadow page tables that are used when > a guest is running a nested context. These structures are allocated on > VCPU_INIT for whole guest, which implies that they may have to be > relocated as the array grows. > > Should a VCPU_INIT occur whilst a vcpu is actively running an L2 and > that the allocation requires relocation, that vcpu will still be > running with a pointer to the previous structure, which will have been > freed. > > Fix this by turning the array of structures to an array of pointers, > which is now allocated at VM creation, sized to the absolute maximum > that KVM can handle. > > In turn, each VCPU_INIT contributes S2_MMU_PER_VCPU to the pool. No > reallocation is ever performed, and the life cycle of each object is > much clearer: > > - the nested_mmus array is allocated in kvm_init_nested(), and freed > in kvm_arch_destroy_vm() > > - s2_mmu structures are allocated in kvm_vcpu_init_nested(), and freed > on kvm_arch_flush_shadow_all() > > Finally, the freeing of vcpu->arch.vncr_array is made consistent > rather than being done on some failure paths, but not others. > > Fixes: 4f128f8e1aaa ("KVM: arm64: nv: Support multiple nested Stage-2 mmu structures") > Reported-by: Shen Yongchao > Reported-by: Karl Mehltretter > Suggested-by: Karl Mehltretter > Link: https://lore.kernel.org/r/20260803224405.41468-1-kmehltretter@gmail.com > Signed-off-by: Marc Zyngier One issue with a typo'd type below (the compiler is ok with it because it's expressed as a sizeof(ptr) but it should be fixed) and a small nit, and also Wei Lin had a comment re: the commit message. With those addressed LGTM so: Acked-by: Lorenzo Stoakes (ARM) > Cc: stable@vger.kernel.org > --- > arch/arm64/include/asm/kvm_host.h | 2 +- > arch/arm64/include/asm/kvm_nested.h | 2 +- > arch/arm64/kvm/arm.c | 8 ++- > arch/arm64/kvm/nested.c | 93 +++++++++++++---------------- > 4 files changed, 51 insertions(+), 54 deletions(-) > > diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h > index 108966a9db12b..08b2f24dc3c79 100644 > --- a/arch/arm64/include/asm/kvm_host.h > +++ b/arch/arm64/include/asm/kvm_host.h > @@ -322,7 +322,7 @@ struct kvm_arch { > * Stage 2 paging state for VMs with nested S2 using a virtual > * VMID. > */ > - struct kvm_s2_mmu *nested_mmus; > + struct kvm_s2_mmu **nested_mmus; OK I see, rather than having to deal with the dynamic array-type stuff and all the mess that comes with that, just allocate at S2_MMU_PER_VCPU granularity, i.e. the amount that can be expanded at any time. > size_t nested_mmus_size; > int nested_mmus_next; > > diff --git a/arch/arm64/include/asm/kvm_nested.h b/arch/arm64/include/asm/kvm_nested.h > index 1ed7083358096..5b8edb2e8a87d 100644 > --- a/arch/arm64/include/asm/kvm_nested.h > +++ b/arch/arm64/include/asm/kvm_nested.h > @@ -66,7 +66,7 @@ static inline u64 translate_ttbr0_el2_to_ttbr0_el1(u64 ttbr0) > > extern bool forward_smc_trap(struct kvm_vcpu *vcpu); > extern bool forward_debug_exception(struct kvm_vcpu *vcpu); > -extern void kvm_init_nested(struct kvm *kvm); > +extern int kvm_init_nested(struct kvm *kvm); > extern int kvm_vcpu_init_nested(struct kvm_vcpu *vcpu); > extern void kvm_init_nested_s2_mmu(struct kvm_s2_mmu *mmu); > extern struct kvm_s2_mmu *lookup_s2_mmu(struct kvm_vcpu *vcpu); > diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c > index 50adfff75be82..7607173c1a40c 100644 > --- a/arch/arm64/kvm/arm.c > +++ b/arch/arm64/kvm/arm.c > @@ -223,8 +223,6 @@ int kvm_arch_init_vm(struct kvm *kvm, unsigned long type) > mutex_unlock(&kvm->lock); > #endif > > - kvm_init_nested(kvm); > - > ret = kvm_share_hyp(kvm, kvm + 1); > if (ret) > return ret; > @@ -239,6 +237,10 @@ int kvm_arch_init_vm(struct kvm *kvm, unsigned long type) > if (ret) > goto err_free_cpumask; > > + ret = kvm_init_nested(kvm); > + if (ret) > + goto err_uninit_mmu; > + > if (is_protected_kvm_enabled()) { > /* > * If any failures occur after this is successful, make sure to > @@ -267,6 +269,7 @@ int kvm_arch_init_vm(struct kvm *kvm, unsigned long type) > > err_uninit_mmu: > kvm_uninit_stage2_mmu(kvm); > + kvfree(kvm->arch.nested_mmus); > err_free_cpumask: > free_cpumask_var(kvm->arch.supported_cpus); > err_unshare_kvm: > @@ -324,6 +327,7 @@ void kvm_arch_destroy_vm(struct kvm *kvm) > > kvm_unshare_hyp(kvm, kvm + 1); > > + kvfree(kvm->arch.nested_mmus); > kvm_arm_teardown_hypercalls(kvm); > } > > diff --git a/arch/arm64/kvm/nested.c b/arch/arm64/kvm/nested.c > index 20af94197a8a7..254cbd8703b3d 100644 > --- a/arch/arm64/kvm/nested.c > +++ b/arch/arm64/kvm/nested.c > @@ -44,11 +44,15 @@ struct vncr_tlb { > */ > #define S2_MMU_PER_VCPU 2 > > -void kvm_init_nested(struct kvm *kvm) > +int kvm_init_nested(struct kvm *kvm) > { > - kvm->arch.nested_mmus = NULL; > + kvm->arch.nested_mmus = kvmalloc_array(KVM_MAX_VCPUS * S2_MMU_PER_VCPU, > + sizeof(struct s2_mmu *), As pointed out by Sashiko/Karl this seems to be a typo, should be kvm_s2_mmu? > + GFP_KERNEL_ACCOUNT); > kvm->arch.nested_mmus_size = 0; > atomic_set(&kvm->arch.vncr_tlb_count, 0); > + > + return kvm->arch.nested_mmus ? 0 : -ENOMEM; > } > > static int init_nested_s2_mmu(struct kvm *kvm, struct kvm_s2_mmu *mmu) > @@ -69,8 +73,9 @@ static int init_nested_s2_mmu(struct kvm *kvm, struct kvm_s2_mmu *mmu) > int kvm_vcpu_init_nested(struct kvm_vcpu *vcpu) > { > struct kvm *kvm = vcpu->kvm; > - struct kvm_s2_mmu *tmp; > - int num_mmus, ret = 0; > + int num_mmus; > + > + lockdep_assert_held(&kvm->arch.config_lock); > > if (test_bit(KVM_ARM_VCPU_HAS_EL2_E2H0, kvm->arch.vcpu_features) && > !cpus_have_final_cap(ARM64_HAS_HCR_NV1)) > @@ -83,51 +88,40 @@ int kvm_vcpu_init_nested(struct kvm_vcpu *vcpu) > if (!vcpu->arch.ctxt.vncr_array) > return -ENOMEM; > > - /* > - * Let's treat memory allocation failures as benign: If we fail to > - * allocate anything, return an error and keep the allocated array > - * alive. Userspace may try to recover by initializing the vcpu > - * again, and there is no reason to affect the whole VM for this. > - */ > num_mmus = atomic_read(&kvm->online_vcpus) * S2_MMU_PER_VCPU; > > if (num_mmus > kvm->arch.nested_mmus_size) { I guess this can only ever be kvm->arch.nested_mmus_size + S2_MMU_PER_VCPU? Maybe worth an assert if so? But not sure how useful it'd be in practice. > - tmp = kvcalloc(num_mmus, sizeof(*tmp), GFP_KERNEL_ACCOUNT); > + struct kvm_s2_mmu *tmp; > + int i, ret = 0; > + > + tmp = kvcalloc(S2_MMU_PER_VCPU, sizeof(*tmp), GFP_KERNEL_ACCOUNT); > if (!tmp) > - return -ENOMEM; > + ret = -ENOMEM; > > - write_lock(&kvm->mmu_lock); Nice to do more stuff outside of the lock. > - > - if (kvm->arch.nested_mmus_size) { > - memcpy(tmp, kvm->arch.nested_mmus, > - size_mul(sizeof(*tmp), kvm->arch.nested_mmus_size)); > - > - for (int i = 0; i < kvm->arch.nested_mmus_size; i++) > - tmp[i].pgt->mmu = &tmp[i]; > + for (i = 0; !ret && i < S2_MMU_PER_VCPU; i++) { > + ret = init_nested_s2_mmu(kvm, &tmp[i]); > + if (ret) > + break; This seems to make the !ret above redundant so maybe: for (i = 0; !ret && i < S2_MMU_PER_VCPU; i++) ret = init_nested_s2_mmu(kvm, &tmp[i]); Or: for (i = 0; i < S2_MMU_PER_VCPU; i++) { ret = init_nested_s2_mmu(kvm, &tmp[i]); if (ret) break; } Which seems a bit clearer. > } > > - swap(kvm->arch.nested_mmus, tmp); > + if (ret) { > + while (--i >= 0) > + kvm_free_stage2_pgd(&tmp[i]); > > - write_unlock(&kvm->mmu_lock); > + kvfree(tmp); > + free_page((unsigned long)vcpu->arch.ctxt.vncr_array); > + vcpu->arch.ctxt.vncr_array = NULL; > + return ret; I seem to remember from my explorations of this that there are some ways in which can get referenced by someone, but again I think you fix all this in 2/2 anyway. > + } > + > + guard(write_lock)(&kvm->mmu_lock); This guard does make it much neater :) > > - kvfree(tmp); > + for (i = 0; i < S2_MMU_PER_VCPU; i++) > + kvm->arch.nested_mmus[i + kvm->arch.nested_mmus_size] = &tmp[i]; > + > + kvm->arch.nested_mmus_size += S2_MMU_PER_VCPU; > } > > - for (int i = kvm->arch.nested_mmus_size; !ret && i < num_mmus; i++) > - ret = init_nested_s2_mmu(kvm, &kvm->arch.nested_mmus[i]); > - > - if (ret) { > - for (int i = kvm->arch.nested_mmus_size; i < num_mmus; i++) > - kvm_free_stage2_pgd(&kvm->arch.nested_mmus[i]); > - > - free_page((unsigned long)vcpu->arch.ctxt.vncr_array); > - vcpu->arch.ctxt.vncr_array = NULL; > - > - return ret; > - } > - > - kvm->arch.nested_mmus_size = num_mmus; > - > return 0; > } > > @@ -741,7 +735,7 @@ void kvm_s2_mmu_iterate_by_vmid(struct kvm *kvm, u16 vmid, > write_lock(&kvm->mmu_lock); > > for (int i = 0; i < kvm->arch.nested_mmus_size; i++) { > - struct kvm_s2_mmu *mmu = &kvm->arch.nested_mmus[i]; > + struct kvm_s2_mmu *mmu = kvm->arch.nested_mmus[i]; > > if (!kvm_s2_mmu_valid(mmu)) > continue; > @@ -783,7 +777,7 @@ struct kvm_s2_mmu *lookup_s2_mmu(struct kvm_vcpu *vcpu) > * if S2 translation is disabled. > */ > for (int i = 0; i < kvm->arch.nested_mmus_size; i++) { > - struct kvm_s2_mmu *mmu = &kvm->arch.nested_mmus[i]; > + struct kvm_s2_mmu *mmu = kvm->arch.nested_mmus[i]; > > if (!kvm_s2_mmu_valid(mmu)) > continue; > @@ -822,7 +816,7 @@ static struct kvm_s2_mmu *get_s2_mmu_nested(struct kvm_vcpu *vcpu) > for (i = kvm->arch.nested_mmus_next; > i < (kvm->arch.nested_mmus_size + kvm->arch.nested_mmus_next); > i++) { > - s2_mmu = &kvm->arch.nested_mmus[i % kvm->arch.nested_mmus_size]; > + s2_mmu = kvm->arch.nested_mmus[i % kvm->arch.nested_mmus_size]; > > if (atomic_read(&s2_mmu->refcnt) == 0) > break; > @@ -1269,7 +1263,7 @@ void kvm_nested_s2_wp(struct kvm *kvm) > return; > > for (i = 0; i < kvm->arch.nested_mmus_size; i++) { > - struct kvm_s2_mmu *mmu = &kvm->arch.nested_mmus[i]; > + struct kvm_s2_mmu *mmu = kvm->arch.nested_mmus[i]; > > if (kvm_s2_mmu_valid(mmu)) > kvm_stage2_wp_range(mmu, 0, kvm_phys_size(mmu)); > @@ -1288,7 +1282,7 @@ void kvm_nested_s2_unmap(struct kvm *kvm, bool may_block) > return; > > for (i = 0; i < kvm->arch.nested_mmus_size; i++) { > - struct kvm_s2_mmu *mmu = &kvm->arch.nested_mmus[i]; > + struct kvm_s2_mmu *mmu = kvm->arch.nested_mmus[i]; > > if (kvm_s2_mmu_valid(mmu)) > kvm_stage2_unmap_range(mmu, 0, kvm_phys_size(mmu), may_block); > @@ -1307,7 +1301,7 @@ void kvm_nested_s2_flush(struct kvm *kvm) > return; > > for (i = 0; i < kvm->arch.nested_mmus_size; i++) { > - struct kvm_s2_mmu *mmu = &kvm->arch.nested_mmus[i]; > + struct kvm_s2_mmu *mmu = kvm->arch.nested_mmus[i]; > > if (kvm_s2_mmu_valid(mmu)) > kvm_stage2_flush_range(mmu, 0, kvm_phys_size(mmu)); > @@ -1316,16 +1310,15 @@ void kvm_nested_s2_flush(struct kvm *kvm) > > void kvm_arch_flush_shadow_all(struct kvm *kvm) > { > - int i; > - > - for (i = 0; i < kvm->arch.nested_mmus_size; i++) { > - struct kvm_s2_mmu *mmu = &kvm->arch.nested_mmus[i]; > + for (int i = kvm->arch.nested_mmus_size - 1; i >= 0; i--) { > + struct kvm_s2_mmu *mmu = kvm->arch.nested_mmus[i]; > > if (!WARN_ON(atomic_read(&mmu->refcnt))) > kvm_free_stage2_pgd(mmu); > + > + if ((i % S2_MMU_PER_VCPU) == 0) > + kvfree(mmu); > } > - kvfree(kvm->arch.nested_mmus); > - kvm->arch.nested_mmus = NULL; > kvm->arch.nested_mmus_size = 0; > kvm_uninit_stage2_mmu(kvm); This is still all racey, but you address it in 2/2. > } > -- > 2.47.3 > > -- Cheers, Lorenzo