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([2001:b07:6468:f312:9af8:e5f5:7516:fa89]) by smtp.googlemail.com with ESMTPSA id a8-20020a170906684800b00993a37aebc5sm983006ejs.50.2023.11.02.04.01.42 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 02 Nov 2023 04:01:44 -0700 (PDT) Message-ID: Date: Thu, 2 Nov 2023 12:01:41 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v13 09/35] KVM: Add KVM_EXIT_MEMORY_FAULT exit to report faults to userspace To: Sean Christopherson , Kai Huang Cc: "viro@zeniv.linux.org.uk" , "aou@eecs.berkeley.edu" , "brauner@kernel.org" , "oliver.upton@linux.dev" , "chenhuacai@kernel.org" , "paul.walmsley@sifive.com" , "palmer@dabbelt.com" , "maz@kernel.org" , "mpe@ellerman.id.au" , "willy@infradead.org" , "anup@brainfault.org" , "akpm@linux-foundation.org" , Xiaoyao Li , "kvm-riscv@lists.infradead.org" , "mic@digikod.net" , "liam.merwick@oracle.com" , "kvm@vger.kernel.org" , Isaku Yamahata , "kirill.shutemov@linux.intel.com" , "david@redhat.com" , "tabba@google.com" , "amoorthy@google.com" , "linuxppc-dev@lists.ozlabs.org" , "michael.roth@amd.com" , "kvmarm@lists.linux.dev" , "linux-kernel@vger.kernel.org" , "linux-fsdevel@vger.kernel.org" , "linux-riscv@lists.infradead.org" , "chao.p.peng@linux.intel.com" , "linux-mips@vger.kernel.org" , Vishal Annapurve , "vbabka@suse.cz" , "mail@maciej.szmigiero.name" , "yu.c.zhang@linux.intel.com" , "qperret@google.com" , "dmatlack@google.com" , Yilun Xu , "isaku.yamahata@gmail.com" , "ackerleytng@google.com" , "jarkko@kernel.org" , "linux-arm-kernel@lists.infradead.org" , "linux-mm@kvack.org" , Wei W Wang References: <20231027182217.3615211-1-seanjc@google.com> <20231027182217.3615211-10-seanjc@google.com> <482bfea6f54ea1bb7d1ad75e03541d0ba0e5be6f.camel@intel.com> From: Paolo Bonzini Autocrypt: addr=pbonzini@redhat.com; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspamd-Queue-Id: 6532040030 X-Rspam-User: X-Stat-Signature: bht8mdf65i8i7qd4ougo9qpskg44gib5 X-Rspamd-Server: rspam01 X-HE-Tag: 1698922910-801319 X-HE-Meta: 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 piKx1D/G 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000330, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 11/1/23 18:36, Sean Christopherson wrote: > A good example is KVM_RUN with -EINTR; if KVM were to return something other than > -EINTR on a pending signal or vcpu->run->immediate_exit, userspace would fall over. And dually if KVM were to return KVM_EXIT_INTR together with something other than -EINTR. > And purging exit_reason super early is subtly tricky because KVM's > (again, poorly documented) ABI is that *some* exit reasons are preserved > across KVM_RUN with vcpu->run->immediate_exit (or with a pending > signal). https://lore.kernel.org/all/ZFFbwOXZ5uI%2Fgdaf@google.com vcpu->run->immediate_exit preserves all exit reasons, but it's not a good idea that immediate_exit behaves different from a pending signal on entry to KVM_RUN (remember that immediate_exit was meant to be a better performing alternative to KVM_SET_SIGNAL_MASK). In principle, vcpu->run->immediate_exit could return KVM_EXIT_INTR (perhaps even _should_, except that breaks selftests so at this point it is ABI). Paolo