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[87.161.166.165]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-3a53229da18sm1116872f8f.19.2025.06.06.00.39.38 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 06 Jun 2025 00:39:40 -0700 (PDT) Message-ID: Date: Fri, 6 Jun 2025 09:39:37 +0200 Precedence: bulk X-Mailing-List: kvm@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v11 14/18] KVM: arm64: Handle guest_memfd-backed guest page faults To: Fuad Tabba , James Houghton Cc: kvm@vger.kernel.org, linux-arm-msm@vger.kernel.org, linux-mm@kvack.org, kvmarm@lists.linux.dev, pbonzini@redhat.com, chenhuacai@kernel.org, mpe@ellerman.id.au, anup@brainfault.org, paul.walmsley@sifive.com, palmer@dabbelt.com, aou@eecs.berkeley.edu, seanjc@google.com, viro@zeniv.linux.org.uk, brauner@kernel.org, willy@infradead.org, akpm@linux-foundation.org, xiaoyao.li@intel.com, yilun.xu@intel.com, chao.p.peng@linux.intel.com, jarkko@kernel.org, amoorthy@google.com, dmatlack@google.com, isaku.yamahata@intel.com, mic@digikod.net, vbabka@suse.cz, vannapurve@google.com, ackerleytng@google.com, mail@maciej.szmigiero.name, michael.roth@amd.com, wei.w.wang@intel.com, liam.merwick@oracle.com, isaku.yamahata@gmail.com, kirill.shutemov@linux.intel.com, suzuki.poulose@arm.com, steven.price@arm.com, quic_eberman@quicinc.com, quic_mnalajal@quicinc.com, quic_tsoni@quicinc.com, quic_svaddagi@quicinc.com, quic_cvanscha@quicinc.com, quic_pderrin@quicinc.com, quic_pheragu@quicinc.com, catalin.marinas@arm.com, james.morse@arm.com, yuzenghui@huawei.com, oliver.upton@linux.dev, maz@kernel.org, will@kernel.org, qperret@google.com, keirf@google.com, roypat@amazon.co.uk, shuah@kernel.org, hch@infradead.org, jgg@nvidia.com, rientjes@google.com, jhubbard@nvidia.com, fvdl@google.com, hughd@google.com, peterx@redhat.com, pankaj.gupta@amd.com, ira.weiny@intel.com References: <20250605153800.557144-1-tabba@google.com> <20250605153800.557144-15-tabba@google.com> From: David Hildenbrand Content-Language: en-US Autocrypt: addr=david@redhat.com; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit >>> + write_fault = kvm_is_write_fault(vcpu); >>> + exec_fault = kvm_vcpu_trap_is_exec_fault(vcpu); >>> + >>> + if (write_fault && exec_fault) { >>> + kvm_err("Simultaneous write and execution fault\n"); >>> + return -EFAULT; >>> + } >>> + >>> + if (is_perm && !write_fault && !exec_fault) { >>> + kvm_err("Unexpected L2 read permission error\n"); >>> + return -EFAULT; >>> + } >> >> I think, ideally, these above checks should be put into a separate >> function and shared with user_mem_abort(). (The VM_BUG_ON(write_fault >> && exec_fault) that user_mem_abort() does seems fine to me, I don't see a >> real need to change it to -EFAULT.) > > I would like to do that, however, I didn't want to change > user_mem_abort(), and regarding the VM_BUG_ON, see David's feedback to > V10: > > https://lore.kernel.org/all/ed1928ce-fc6f-4aaa-9f54-126a8af12240@redhat.com/ Worth reading Linus' reply in [1], that contains a bit more history on BUG_ON() and how it should not be used. (VM_BUG_ON we'll now likely get rid of completely) [1] https://lkml.kernel.org/r/20250604140544.688711-1-david@redhat.com -- Cheers, David / dhildenb