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Wed, 31 Jul 2024 02:50:40 -0700 (PDT) X-Google-Smtp-Source: AGHT+IHm0sw2f7Q/hSxPLtTI3KYQw5uCrmW/NKDuI5rQ7HlgfsjazxGbnWK3KS2H8Xhx5SNKvtVQug== X-Received: by 2002:a17:907:94cb:b0:a7a:bece:6223 with SMTP id a640c23a62f3a-a7d3ff7b8e4mr1064728266b.6.1722419440130; Wed, 31 Jul 2024 02:50:40 -0700 (PDT) Received: from [192.168.10.81] ([151.95.101.29]) by smtp.googlemail.com with ESMTPSA id a640c23a62f3a-a7acad93105sm746255566b.167.2024.07.31.02.50.38 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 31 Jul 2024 02:50:39 -0700 (PDT) Message-ID: <57ba7e1d-0121-4d71-89b8-c61c476ca724@redhat.com> Date: Wed, 31 Jul 2024 11:50:38 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v12 84/84] KVM: Don't grab reference on VM_MIXEDMAP pfns that have a "struct page" To: Sean Christopherson Cc: Marc Zyngier , Oliver Upton , Tianrui Zhao , Bibo Mao , Huacai Chen , Michael Ellerman , Anup Patel , Paul Walmsley , Palmer Dabbelt , Albert Ou , Christian Borntraeger , Janosch Frank , Claudio Imbrenda , kvm@vger.kernel.org, linux-arm-kernel@lists.infradead.org, kvmarm@lists.linux.dev, 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, David Matlack , David Stevens References: <20240726235234.228822-1-seanjc@google.com> <20240726235234.228822-85-seanjc@google.com> <992c4a07-fb84-42d8-93b3-96fb3a12c8e0@redhat.com> From: Paolo Bonzini Autocrypt: addr=pbonzini@redhat.com; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20240731_025048_140588_67BFB2AA X-CRM114-Status: GOOD ( 11.94 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On 7/30/24 22:21, Sean Christopherson wrote: > On Tue, Jul 30, 2024, Paolo Bonzini wrote: >> On 7/27/24 01:52, Sean Christopherson wrote: >>> Now that KVM no longer relies on an ugly heuristic to find its struct page >>> references, i.e. now that KVM can't get false positives on VM_MIXEDMAP >>> pfns, remove KVM's hack to elevate the refcount for pfns that happen to >>> have a valid struct page. In addition to removing a long-standing wart >>> in KVM, this allows KVM to map non-refcounted struct page memory into the >>> guest, e.g. for exposing GPU TTM buffers to KVM guests. >> >> Feel free to leave it to me for later, but there are more cleanups that >> can be made, given how simple kvm_resolve_pfn() is now: > > I'll revisit kvm_resolve_pfn(), Maxim also wasn't a fan of a similar helper that > existed in v11. FWIW kvm_resolve_pfn() is totally fine as an intermediate step. Just food for thought for possible follow-ups. >> Also, check_user_page_hwpoison() should not be needed anymore, probably >> not since commit 234b239bea39 ("kvm: Faults which trigger IO release the >> mmap_sem", 2014-09-24) removed get_user_pages_fast() from hva_to_pfn_slow(). > > Ha, I *knew* this sounded familiar. Past me apparently came to the same > conclusion[*], though I wrongly suspected a memory leak and promptly forgot to > ever send a patch. I'll tack one on this time around. As you prefer. Paolo