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[60.242.147.73]) by smtp.gmail.com with ESMTPSA id o20sm2094410pjq.57.2021.06.24.03.17.47 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 24 Jun 2021 03:17:48 -0700 (PDT) Date: Thu, 24 Jun 2021 20:17:42 +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> In-Reply-To: <1624528342.s2ezcyp90x.astroid@bobo.none> MIME-Version: 1.0 Message-Id: <1624529635.75a1ann91v.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 Nicholas Piggin's message of June 24, 2021 7:57 pm: > Excerpts from Paolo Bonzini's message of June 24, 2021 7:42 pm: >> On 24/06/21 10:52, Nicholas Piggin wrote: >>>> For now, wrap all calls to gfn_to_pfn functions in the new helper >>>> function. Callers which don't need the page struct will be updated in >>>> follow-up patches. >>> Hmm. You mean callers that do need the page will be updated? Normally >>> if there will be leftover users that don't need the struct page then >>> you would go the other way and keep the old call the same, and add a ne= w >>> one (gfn_to_pfn_page) just for those that need it. >>=20 >> Needing kvm_pfn_page_unwrap is a sign that something might be buggy, so=20 >> it's a good idea to move the short name to the common case and the ugly=20 >> kvm_pfn_page_unwrap(gfn_to_pfn(...)) for the weird one. In fact I'm not= =20 >> sure there should be any kvm_pfn_page_unwrap in the end. >=20 > 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. >=20 > But yes in the end you would either need to make gfn_to_pfn never return > a page found via follow_pte, or change all callers to the new way. If=20 > 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. And are gfn_to_page cases also vulernable to the same issue? So I think it could be marked deprecated or something if not everything=20 will be converted in the one series, and don't need to touch all that=20 arch code with this patch. Thanks, Nick