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[60.242.147.73]) by smtp.gmail.com with ESMTPSA id i8sm2522609pfq.165.2021.06.24.03.42.13 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 24 Jun 2021 03:42:14 -0700 (PDT) Date: Thu, 24 Jun 2021 20:42:08 +1000 From: Nicholas Piggin Subject: Re: [PATCH 2/6] KVM: mmu: also return page from gfn_to_pfn To: Aleksandar Markovic , Huacai Chen , Marc Zyngier , Paul Mackerras , Paolo Bonzini , David Stevens , Zhenyu Wang , Zhi Wang Cc: Alexandru Elisei , dri-devel@lists.freedesktop.org, intel-gfx@lists.freedesktop.org, intel-gvt-dev@lists.freedesktop.org, James Morse , Jim Mattson , Joerg Roedel , kvmarm@lists.cs.columbia.edu, kvm-ppc@vger.kernel.org, kvm@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, linux-mips@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, Sean Christopherson , Suzuki K Poulose , Vitaly Kuznetsov , Wanpeng Li , Will Deacon References: <20210624035749.4054934-1-stevensd@google.com> <20210624035749.4054934-3-stevensd@google.com> <1624524331.zsin3qejl9.astroid@bobo.none> <201b68a7-10ea-d656-0c1e-5511b1f22674@redhat.com> <1624528342.s2ezcyp90x.astroid@bobo.none> <1624529635.75a1ann91v.astroid@bobo.none> In-Reply-To: MIME-Version: 1.0 Message-Id: <1624531085.fax3fcqpgc.astroid@bobo.none> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org Excerpts from Paolo Bonzini's message of June 24, 2021 8:21 pm: > On 24/06/21 12:17, Nicholas Piggin wrote: >>> If all callers were updated that is one thing, but from the changelog >>> it sounds like that would not happen and there would be some gfn_to_pfn >>> users left over. >>> >>> But yes in the end you would either need to make gfn_to_pfn never retur= n >>> a page found via follow_pte, or change all callers to the new way. If >>> the plan is for the latter then I guess that's fine. >> >> Actually in that case anyway I don't see the need -- the existence of >> gfn_to_pfn is enough to know it might be buggy. It can just as easily >> be grepped for as kvm_pfn_page_unwrap. >=20 > Sure, but that would leave us with longer function names=20 > (gfn_to_pfn_page* instead of gfn_to_pfn*). So the "safe" use is the one=20 > that looks worse and the unsafe use is the one that looks safe. The churn isn't justified because of function name length. Choose g2pp()=20 if you want a non-descriptive but short name. The existing name isn't good anyway because it not only looks up a pfn=20 but also a page, and more importantly it gets a ref on the page. The name should be changed if you introduce a new API. >> And are gfn_to_page cases also >> vulernable to the same issue? >=20 > No, they're just broken for the VM_IO|VM_PFNMAP case. No they aren't vulnerable, or they are vunlerable but also broken in=20 other cases? Thanks, Nick