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Wed, 26 Feb 2025 10:38:29 -0800 (PST) X-Google-Smtp-Source: AGHT+IGCDnvlNLlcOiBeBNB6S3TtqOxMTUK/PR46JW7lLq0KgREP2FusBvOHa60dTZ6MWayPAjFhrw== X-Received: by 2002:a17:906:6185:b0:ab7:c1d5:14f9 with SMTP id a640c23a62f3a-abeeecf6f63mr518730666b.10.1740595109199; Wed, 26 Feb 2025 10:38:29 -0800 (PST) Received: from [192.168.10.81] ([176.206.102.52]) by smtp.googlemail.com with ESMTPSA id a640c23a62f3a-abed20ac11bsm364226166b.163.2025.02.26.10.38.23 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 26 Feb 2025 10:38:28 -0800 (PST) Message-ID: Date: Wed, 26 Feb 2025 19:38:21 +0100 X-Mailing-List: linuxppc-dev@lists.ozlabs.org List-Id: List-Help: List-Owner: List-Post: List-Archive: , List-Subscribe: , , List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 0/7] KVM: x86: nVMX IRQ fix and VM teardown cleanups To: Sean Christopherson , Marc Zyngier , Oliver Upton , Tianrui Zhao , Bibo Mao , Huacai Chen , Madhavan Srinivasan , Anup Patel , Paul Walmsley , Palmer Dabbelt , Albert Ou , Christian Borntraeger , Janosch Frank , Claudio Imbrenda Cc: linux-arm-kernel@lists.infradead.org, kvmarm@lists.linux.dev, kvm@vger.kernel.org, loongarch@lists.linux.dev, linux-mips@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, kvm-riscv@lists.infradead.org, linux-riscv@lists.infradead.org, linux-kernel@vger.kernel.org, Aaron Lewis , Jim Mattson , Yan Zhao , Rick P Edgecombe , Kai Huang , Isaku Yamahata References: <20250224235542.2562848-1-seanjc@google.com> From: Paolo Bonzini Autocrypt: addr=pbonzini@redhat.com; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 2/25/25 00:55, Sean Christopherson wrote: > This was _supposed_ to be a tiny one-off patch to fix a nVMX bug where KVM > fails to detect that, after nested VM-Exit, L1 has a pending IRQ (or NMI). > But because x86's nested teardown flows are garbage (KVM simply forces a > nested VM-Exit to put the vCPU back into L1), that simple fix snowballed. > > The immediate issue is that checking for a pending interrupt accesses the > legacy PIC, and x86's kvm_arch_destroy_vm() currently frees the PIC before > destroying vCPUs, i.e. checking for IRQs during the forced nested VM-Exit > results in a NULL pointer deref (or use-after-free if KVM didn't nullify > the PIC pointer). That's patch 1. > > Patch 2 is the original nVMX fix. > > The remaining patches attempt to bring a bit of sanity to x86's VM > teardown code, which has accumulated a lot of cruft over the years. E.g. > KVM currently unloads each vCPU's MMUs in a separate operation from > destroying vCPUs, all because when guest SMP support was added, KVM had a > kludgy MMU teardown flow that broken when a VM had more than one 1 vCPU. > And that oddity lived on, for 18 years... Queued patches 1 and 2 to kvm/master, and everything to kvm/queue (pending a little more testing and the related TDX change). Paolo