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[104.155.91.135]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-486eb33e020sm34226386f8f.18.2026.09.15.00.41.15 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 15 Sep 2026 00:41:15 -0700 (PDT) Date: Tue, 15 Sep 2026 08:41:12 +0100 From: Vincent Donnefort To: Fuad Tabba Cc: maz@kernel.org, oupton@kernel.org, kvmarm@lists.linux.dev, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, catalin.marinas@arm.com, will@kernel.org, joey.gouly@arm.com, seiden@linux.ibm.com, suzuki.poulose@arm.com, yuzenghui@huawei.com, mark.rutland@arm.com, steven.price@arm.com, qperret@google.com, tabba@google.com Subject: Re: [PATCH v2 2/2] KVM: arm64: Pin the host vCPU before adjusting its PC under pKVM Message-ID: References: <20260915070418.3209779-1-fuad.tabba@linux.dev> <20260915070418.3209779-3-fuad.tabba@linux.dev> Precedence: bulk X-Mailing-List: kvmarm@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260915070418.3209779-3-fuad.tabba@linux.dev> On Tue, Sep 15, 2026 at 08:04:18AM +0100, Fuad Tabba wrote: > Under pKVM, a page the host shares with EL2 is mapped at EL2 only while > it's pinned, and the host vCPU is pinned at its first KVM_RUN. > KVM_SET_VCPU_EVENTS with ext_dabt_pending reaches __kvm_adjust_pc() at > EL2 before that, and dereferencing the unmapped host vCPU panics the > hypervisor. Any process holding /dev/kvm on a pKVM host can trigger it. > > Pin the host vCPU around the adjustment when no hyp vCPU is loaded for > it. A loaded hyp vCPU implies it's pinned. A pin fails only for memory > the host never shared, and the request is then dropped like any other > bad host pointer. > > Fixes: efa1368ba9f4b ("KVM: arm64: Commit exceptions from KVM_SET_VCPU_EVENTS immediately") > Cc: stable@vger.kernel.org > Signed-off-by: Fuad Tabba > --- > arch/arm64/kvm/hyp/nvhe/hyp-main.c | 19 ++++++++++++++++++- > 1 file changed, 18 insertions(+), 1 deletion(-) > > diff --git a/arch/arm64/kvm/hyp/nvhe/hyp-main.c b/arch/arm64/kvm/hyp/nvhe/hyp-main.c > index 9a3b92e626adb..4cb7347db2514 100644 > --- a/arch/arm64/kvm/hyp/nvhe/hyp-main.c > +++ b/arch/arm64/kvm/hyp/nvhe/hyp-main.c > @@ -542,8 +542,25 @@ static void handle___pkvm_host_mkyoung_guest(struct kvm_cpu_context *host_ctxt) > static void handle___kvm_adjust_pc(struct kvm_cpu_context *host_ctxt) > { > DECLARE_REG(struct kvm_vcpu *, vcpu, host_ctxt, 1); > + struct pkvm_hyp_vcpu *hyp_vcpu; > + struct kvm_vcpu *host_vcpu; > > - __kvm_adjust_pc(kern_hyp_va(vcpu)); > + host_vcpu = __get_host_hyp_vcpus(vcpu, &hyp_vcpu); > + if (host_vcpu) { > + __kvm_adjust_pc(host_vcpu); > + return; > + } > + > + /* > + * With no hyp vCPU loaded for it, the host vCPU may be unpinned, > + * and so unmapped at EL2: its first run pins it. > + */ > + host_vcpu = kern_hyp_va(vcpu); > + if (hyp_pin_shared_mem(host_vcpu, host_vcpu + 1)) > + return; > + > + __kvm_adjust_pc(host_vcpu); > + hyp_unpin_shared_mem(host_vcpu, host_vcpu + 1); > } > > static void handle___kvm_flush_vm_context(struct kvm_cpu_context *host_ctxt) > -- > 2.39.5 > Reviewed-by: Vincent Donnefort -- Vincent