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Thu, 01 Aug 2024 02:21:02 -0700 (PDT) Received: from draig.lan ([85.9.250.243]) by smtp.gmail.com with ESMTPSA id 4fb4d7f45d1cf-5b017787967sm7857844a12.9.2024.08.01.02.21.00 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 01 Aug 2024 02:21:01 -0700 (PDT) Received: from draig (localhost [IPv6:::1]) by draig.lan (Postfix) with ESMTP id 51C785F80C; Thu, 1 Aug 2024 10:20:59 +0100 (BST) From: =?utf-8?Q?Alex_Benn=C3=A9e?= To: Sean Christopherson Cc: Paolo Bonzini , 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 Subject: Re: [PATCH v12 05/84] KVM: Add kvm_release_page_unused() API to put pages that KVM never consumes In-Reply-To: <20240726235234.228822-6-seanjc@google.com> (Sean Christopherson's message of "Fri, 26 Jul 2024 16:51:14 -0700") References: <20240726235234.228822-1-seanjc@google.com> <20240726235234.228822-6-seanjc@google.com> Date: Thu, 01 Aug 2024 10:20:59 +0100 Message-ID: <87wml0egzo.fsf@draig.linaro.org> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20240801_022105_731744_F9FFEAA7 X-CRM114-Status: GOOD ( 17.68 ) 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 Sean Christopherson writes: > Add an API to release an unused page, i.e. to put a page without marking > it accessed or dirty. The API will be used when KVM faults-in a page but > bails before installing the guest mapping (and other similar flows). > > Signed-off-by: Sean Christopherson > --- > include/linux/kvm_host.h | 9 +++++++++ > 1 file changed, 9 insertions(+) > > diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h > index 3d9617d1de41..c5d39a337aa3 100644 > --- a/include/linux/kvm_host.h > +++ b/include/linux/kvm_host.h > @@ -1201,6 +1201,15 @@ unsigned long gfn_to_hva_prot(struct kvm *kvm, gfn= _t gfn, bool *writable); > unsigned long gfn_to_hva_memslot(struct kvm_memory_slot *slot, gfn_t gfn= ); > unsigned long gfn_to_hva_memslot_prot(struct kvm_memory_slot *slot, gfn_= t gfn, > bool *writable); > + > +static inline void kvm_release_page_unused(struct page *page) > +{ > + if (!page) > + return; > + > + put_page(page); > +} I guess it's unfamiliarity with the mm layout but I was trying to find where the get_pages come from to see the full pattern of allocate and return. I guess somewhere in the depths of hva_to_pfn() from hva_to_pfn_retry()? I think the indirection of the page walking confuses me ;-) Anyway the API seems reasonable enough given the other kvm_release_ functions. Reviewed-by: Alex Benn=C3=A9e --=20 Alex Benn=C3=A9e Virtualisation Tech Lead @ Linaro