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[2a02:3100:b105:e101:a437:493a:4de9:ee3e]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-4995ea27ef0sm60747585e9.9.2026.08.07.10.08.18 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 07 Aug 2026 10:08:19 -0700 (PDT) Date: Fri, 7 Aug 2026 19:08:17 +0200 From: Karl Mehltretter To: Marc Zyngier Cc: Oliver Upton , Fuad Tabba , Joey Gouly , Steffen Eiden , Suzuki K Poulose , Zenghui Yu , Catalin Marinas , Will Deacon , linux-arm-kernel@lists.infradead.org, kvmarm@lists.linux.dev, linux-kernel@vger.kernel.org, stable@vger.kernel.org Subject: Re: [PATCH 1/2] KVM: arm64: nv: Allocate the shadow S2 MMUs individually Message-ID: References: <20260803224405.41468-1-kmehltretter@gmail.com> <86mrv2arf2.wl-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: <86mrv2arf2.wl-maz@kernel.org> On Tue, Aug 04, 2026 at 03:31:13PM +0100, Marc Zyngier wrote: > See the hack below that seems to work OK. > Hi Marc, Since error handling has come up again, I should clarify why v2 did not use this sketch verbatim. > - kvm_init_nested(kvm); > + ret = kvm_init_nested(kvm); > + if (ret) > + return ret; > > ret = kvm_share_hyp(kvm, kvm + 1); > if (ret) Once kvm_init_nested() has allocated the pointer table, failure in kvm_share_hyp() or any subsequent VM initialisation step leaks that table. v2 therefore calls kvm_init_nested() after the earlier initialisation steps have succeeded and frees the table if a later step in kvm_arch_init_vm() fails. > + for (int i = 0; !ret && i < S2_MMU_PER_VCPU; i++) > + ret = init_nested_s2_mmu(kvm, &tmp[i]); > + if (ret) { > + for (int i = 0; i < S2_MMU_PER_VCPU; i++) > + kvm_free_stage2_pgd(&tmp[i]); This cleanup includes the entry whose initialisation failed and any entries whose initialisation was never attempted. An uninitialised entry has no valid mmu->arch, but kvm_free_stage2_pgd() immediately derives kvm from mmu->arch before checking mmu->pgt. It can therefore dereference an invalid pointer. This is why v2 tracks successfully initialised MMUs and frees only those entries. Thanks, Karl