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Wed, 31 Jul 2024 13:36:26 -0700 (PDT) Date: Wed, 31 Jul 2024 13:36:25 -0700 In-Reply-To: <87a5hxfs3d.fsf@draig.linaro.org> Mime-Version: 1.0 References: <20240726235234.228822-1-seanjc@google.com> <20240726235234.228822-2-seanjc@google.com> <87a5hxfs3d.fsf@draig.linaro.org> Message-ID: Subject: Re: [PATCH v12 01/84] KVM: arm64: Release pfn, i.e. put page, if copying MTE tags hits ZONE_DEVICE From: Sean Christopherson To: "Alex =?utf-8?Q?Benn=C3=A9e?=" 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 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-20240731_133628_726091_81ED6272 X-CRM114-Status: GOOD ( 18.63 ) 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 Wed, Jul 31, 2024, Alex Benn=C3=A9e wrote: > Sean Christopherson writes: >=20 > > Put the page reference acquired by gfn_to_pfn_prot() if > > kvm_vm_ioctl_mte_copy_tags() runs into ZONE_DEVICE memory. KVM's less- > > than-stellar heuristics for dealing with pfn-mapped memory means that K= VM > > can get a page reference to ZONE_DEVICE memory. > > > > Fixes: f0376edb1ddc ("KVM: arm64: Add ioctl to fetch/store tags in a gu= est") > > Signed-off-by: Sean Christopherson > > --- > > arch/arm64/kvm/guest.c | 1 + > > 1 file changed, 1 insertion(+) > > > > diff --git a/arch/arm64/kvm/guest.c b/arch/arm64/kvm/guest.c > > index 11098eb7eb44..e1f0ff08836a 100644 > > --- a/arch/arm64/kvm/guest.c > > +++ b/arch/arm64/kvm/guest.c > > @@ -1059,6 +1059,7 @@ int kvm_vm_ioctl_mte_copy_tags(struct kvm *kvm, > > page =3D pfn_to_online_page(pfn); > > if (!page) { > > /* Reject ZONE_DEVICE memory */ > > + kvm_release_pfn_clean(pfn); >=20 > I guess this gets renamed later in the series. >=20 > However my main comment is does lack of page always mean a ZONE_DEVICE? Nope. > Looking at pfn_to_online_page() I see a bunch of other checks first. Why > isn't it that functions responsibility to clean up after itself if its > returning NULLs? pfn_to_online_page() is more strict than gfn_to_pfn_prot(). At least in th= eory, gfn_to_pfn_prot() could return a pfn that has an associated "struct page", = with a reference held to said page. But for that same pfn, pfn_to_online_page()= could return NULL, in which case KVM needs to put the reference it acquired via gfn_to_pfn_prot().