From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 8DBC5C5CFCF for ; Wed, 12 Aug 2026 14:02:49 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender:List-Subscribe:List-Help :List-Post:List-Archive:List-Unsubscribe:List-Id:Content-Type:MIME-Version: References:In-Reply-To:Subject:Cc:To:From:Message-ID:Date:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=fm2lkQQTeatuHGurNh7/1ULP0hoNWqxW+N4geEJMvaQ=; b=oN7sXzGG63/tzsiM4SvEvM4ono R4wW68TsjvyEJk1Np7FzWT/t+K1NI9LbUDVORuYmH3uyvkaKo8KHPuEmMMnfzmvMgG5Aew8cz6ZeK OfLNkWBHbM4Zh3PPAcxECFNN4HLxvuYI4GlrnzVrpanmitEAu4W1oEyZTyeGHmJPR0WadCSg7RfH2 AUSP9r/wjiMWwho/u846R/IXFU3hltTE3XpAoHjbrEsosZaxsBWfQdAyXggl/D9hD25YPNMh9XZGD OK62+aWO7ldZgetwqAMrc1c6txKnLdCcwOKhc/O8m9k9rp6C7kWRxLqUsoP4O/aAlUqwiO5C4ssai vBXkRyaQ==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.99.1 #2 (Red Hat Linux)) id 1wu9XR-0000000GLGW-1Cre; Wed, 12 Aug 2026 14:02:37 +0000 Received: from sea.source.kernel.org ([172.234.252.31]) by bombadil.infradead.org with esmtps (Exim 4.99.1 #2 (Red Hat Linux)) id 1wu9XQ-0000000GLGC-1ZU1 for linux-arm-kernel@lists.infradead.org; Wed, 12 Aug 2026 14:02:36 +0000 Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) by sea.source.kernel.org (Postfix) with ESMTP id D2A6741E49; Wed, 12 Aug 2026 14:02:35 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id B47D21F00A3A; Wed, 12 Aug 2026 14:02:35 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1786543355; bh=fm2lkQQTeatuHGurNh7/1ULP0hoNWqxW+N4geEJMvaQ=; h=Date:From:To:Cc:Subject:In-Reply-To:References; b=DvNIQ975LyKKF4Z2fXIGSbRsV/QRYPF1yCnmpNjRpQkAoGLnLRUrPgM9y+wt14GRA 3c0ssLb3l+t9MZksJR1rv2y/IoS06rKmTxvWfKclMdSDyKi8HD6yUxFT/1KBOtF3yn pEtVXLHxo6eLUgzYWqpTk3eFb+wtCSgbTiCPeBPkd4Aw8K6odvl9xSlSh4MgLofHaO QKFMeLGfEJdoQ9cCBZyj0o7MQ7sgWyjb9nbzB300GUSopQpIYZL3SIQ6uLPCS24XJn VkaRd1PdUxzuNBYW9+pDf3mh+a9Y/lL+PzFl6GdznhdFUOqnzW9KeOACVjmYFwsty+ OE8EgYR1h3UUg== Received: from sofa.misterjones.org ([185.219.108.64] helo=goblin-girl.misterjones.org) by disco-boy.misterjones.org with esmtpsa (TLS1.3) tls TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 (Exim 4.98.2) (envelope-from ) id 1wu9XN-0000000ExQm-1KYL; Wed, 12 Aug 2026 14:02:33 +0000 Date: Wed, 12 Aug 2026 15:02:32 +0100 Message-ID: <86ik5f1lon.wl-maz@kernel.org> From: Marc Zyngier To: Joey Gouly 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 In-Reply-To: References: <20260811122057.754772-1-maz@kernel.org> User-Agent: Wanderlust/2.15.9 (Almost Unreal) SEMI-EPG/1.14.7 (Harue) FLIM-LB/1.14.9 (=?UTF-8?B?R29qxY0=?=) APEL-LB/10.8 EasyPG/1.0.0 Emacs/30.1 (aarch64-unknown-linux-gnu) MULE/6.0 (HANACHIRUSATO) MIME-Version: 1.0 (generated by SEMI-EPG 1.14.7 - "Harue") Content-Type: text/plain; charset=US-ASCII X-SA-Exim-Connect-IP: 185.219.108.64 X-SA-Exim-Rcpt-To: joey.gouly@arm.com, kvmarm@lists.linux.dev, linux-arm-kernel@lists.infradead.org, seiden@linux.ibm.com, suzuki.poulose@arm.com, oupton@kernel.org, yuzenghui@huawei.com, fuad.tabba@linux.dev, grayhat@foxmail.com, kmehltretter@gmail.com, stable@vger.kernel.org X-SA-Exim-Mail-From: maz@kernel.org X-SA-Exim-Scanned: No (on disco-boy.misterjones.org); SAEximRunCond expanded to false 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 Hi Joey, On Wed, 12 Aug 2026 12:21:35 +0100, Joey Gouly wrote: > > 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()) Yeah, this looks like Sashiko went south again. You'd hope it'd be able to follow such a simple code path... > > So maybe a > > lockdep_assert_held(&kvm->arch.config_lock); > > makes sense in kvm_vcpu_init_nested()? Sure, that's never a bad thing to add. Thanks, M. -- Without deviation from the norm, progress is not possible.