From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by smtp.subspace.kernel.org (Postfix) with ESMTP id CAF244399DC for ; Wed, 12 Aug 2026 11:21:43 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=217.140.110.172 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1786533706; cv=none; b=Ycw7du7DmHuK0ps6JhT6iS2omuJoli2VyJX6L/pWouy7L9balOEAA08AMHKIgKiQRjhAYtggsEw5jnEClVRCBIQNE2IAWTv9zXw7CW4FVz0qmFZ15Zht68YOpow/0zmKmGayEItAJfLsGpJH72xQNTRZbHtmk1ugR3EP2OVuT2k= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1786533706; c=relaxed/simple; bh=uc8UMTUcAc8ZS/P+6zbuB/2Y5u+uo+jypF+mtHt96pE=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=CIOvn8PvCblBBCCT5gGN8WDcFsRNc+Rju4BZVsv7FV5pWbxyp+wyo4Rif+iRKF89vqpM2D39kCDxxsV+PVj2eCqS3+r+aMbxFroB42VazSimEse+5BO+AVD3db+psRpasdSUMxDt0dMc6rBVUPAM7aEtNgDKk94kco50w3RgQmk= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com; spf=pass smtp.mailfrom=arm.com; dkim=pass (1024-bit key) header.d=arm.com header.i=@arm.com header.b=ekPfEqaV; arc=none smtp.client-ip=217.140.110.172 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=arm.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=arm.com header.i=@arm.com header.b="ekPfEqaV" Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 01F161682; Wed, 12 Aug 2026 04:21:39 -0700 (PDT) Received: from e143914.arm.com (e143914.arm.com [10.2.213.21]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 15DEC3F632; Wed, 12 Aug 2026 04:21:40 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=simple/simple; d=arm.com; s=foss; t=1786533702; bh=uc8UMTUcAc8ZS/P+6zbuB/2Y5u+uo+jypF+mtHt96pE=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=ekPfEqaVCpaAXY6MbA6c2uUF2x/vChiTFrl+sZEaEeIKaGHASaoEctkvB7NDS5qAm PQtiEK3PgUp7SvcMdLGsJokNrbEtsEgWJyeH9k95+KVbCPXDpkPgenhfWhcrPuwA++ 8nnibAEVoFlzWR5a9vd/ZTEhMitRodi1fROi8hCY= Date: Wed, 12 Aug 2026 12:21:35 +0100 From: Joey Gouly To: Marc Zyngier Cc: kvmarm@lists.linux.dev, linux-arm-kernel@lists.infradead.org, Steffen Eiden , Suzuki K Poulose , Oliver Upton , Zenghui Yu , Fuad Tabba , Shen Yongchao , Karl Mehltretter , stable@vger.kernel.org Subject: Re: [PATCH] KVM: arm64: nv: Fix life cycle of the nested_mmus array Message-ID: References: <20260811122057.754772-1-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: <20260811122057.754772-1-maz@kernel.org> Hi, Small comment / suggestion. On Tue, Aug 11, 2026 at 01:20:57PM +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 > Cc: stable@vger.kernel.org > --- > > Notes: > Sending this as a first class patch, since the other approaches were even > uglier than this one. I'm still displeased with kvm_arch_flush_shadow_all(), > but that's a step in the direction of tightening it: > > 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 | 91 +++++++++++++---------------- > 4 files changed, 49 insertions(+), 54 deletions(-) > [..] > diff --git a/arch/arm64/kvm/nested.c b/arch/arm64/kvm/nested.c > index 20af94197a8a7..50d6dcc75582c 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 *), > + 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 +73,7 @@ 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; > > if (test_bit(KVM_ARM_VCPU_HAS_EL2_E2H0, kvm->arch.vcpu_features) && > !cpus_have_final_cap(ARM64_HAS_HCR_NV1)) > @@ -83,51 +86,40 @@ 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) { Sashiko.dev complained about a possible race here, but looking at the code, it seems incorrect? Unsure why it didn't e-mail it. https://sashiko.dev/#/patchset/20260811122057.754772-1-maz%40kernel.org It seems that this code is serialised / protected by kvm->arch.config_lock in __kvm_vcpu_set_target() (which is the only caller of kvm_vcpu_init_nested() via kvm_setup_vcpu()) So maybe a lockdep_assert_held(&kvm->arch.config_lock); makes sense in kvm_vcpu_init_nested()? Thanks, Joey