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AJvYcCVtb9M7EaW4Gd3qECIoEqTqD2rYe2oKY3b15syh0UlD38z6K9j/ejeGcB67ZAmfyOCx/kRDxn+aOdLr9nCBjIuETwr/PXIrDOKFbigi X-Gm-Message-State: AOJu0Yw4LYe5iYvgTj2X1UbQx7qCgmDW4BzRntoUzK2UWjw3QEPSinQL 9JjJiBXnYvJVvzKDMh0tcKG1XTIzAtyOaRj+fMNFJJzfsgWI2A89D//q74AngTLOIfslRDbKjHD nHg== X-Google-Smtp-Source: AGHT+IHtdYLzf8VxCow9ze9t5PB7b90MwNFbCURT1XZzWgwcWEIftZd8Pqph9MK+hSFYPsX4JKQKNB1AEe8= X-Received: from zagreus.c.googlers.com ([fda3:e722:ac3:cc00:7f:e700:c0a8:5c37]) (user=seanjc job=sendgmr) by 2002:a05:6902:1889:b0:dfb:1147:cbaa with SMTP id 3f1490d57ef6-e0b5459b0b9mr34694276.10.1722038113838; Fri, 26 Jul 2024 16:55:13 -0700 (PDT) Reply-To: Sean Christopherson Date: Fri, 26 Jul 2024 16:52:24 -0700 In-Reply-To: <20240726235234.228822-1-seanjc@google.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20240726235234.228822-1-seanjc@google.com> X-Mailer: git-send-email 2.46.0.rc1.232.g9752f9e123-goog Message-ID: <20240726235234.228822-76-seanjc@google.com> Subject: [PATCH v12 75/84] KVM: Add support for read-only usage of gfn_to_page() From: Sean Christopherson To: 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 , Sean Christopherson Cc: 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-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" Rework gfn_to_page() to support read-only accesses so that it can be used by arm64 to get MTE tags out of guest memory. Opportunistically rewrite the comment to be even more stern about using gfn_to_page(), as there are very few scenarios where requiring a struct page is actually the right thing to do (though there are such scenarios). Add a FIXME to call out that KVM probably should be pinning pages, not just getting pages. Signed-off-by: Sean Christopherson --- include/linux/kvm_host.h | 7 ++++++- virt/kvm/kvm_main.c | 15 ++++++++------- 2 files changed, 14 insertions(+), 8 deletions(-) diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h index 91341cdc6562..f2d3c3c436cc 100644 --- a/include/linux/kvm_host.h +++ b/include/linux/kvm_host.h @@ -1198,7 +1198,12 @@ void kvm_arch_flush_shadow_memslot(struct kvm *kvm, int kvm_prefetch_pages(struct kvm_memory_slot *slot, gfn_t gfn, struct page **pages, int nr_pages); =20 -struct page *gfn_to_page(struct kvm *kvm, gfn_t gfn); +struct page *__gfn_to_page(struct kvm *kvm, gfn_t gfn, bool write); +static inline struct page *gfn_to_page(struct kvm *kvm, gfn_t gfn) +{ + return __gfn_to_page(kvm, gfn, true); +} + unsigned long gfn_to_hva(struct kvm *kvm, gfn_t gfn); 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); diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c index d0f55a6ecb31..16bc3ac3ff84 100644 --- a/virt/kvm/kvm_main.c +++ b/virt/kvm/kvm_main.c @@ -3174,25 +3174,26 @@ int kvm_prefetch_pages(struct kvm_memory_slot *slot= , gfn_t gfn, EXPORT_SYMBOL_GPL(kvm_prefetch_pages); =20 /* - * Do not use this helper unless you are absolutely certain the gfn _must_= be - * backed by 'struct page'. A valid example is if the backing memslot is - * controlled by KVM. Note, if the returned page is valid, it's refcount = has - * been elevated by gfn_to_pfn(). + * Don't use this API unless you are absolutely, positively certain that K= VM + * needs to get a struct page, e.g. to pin the page for firmware DMA. + * + * FIXME: Users of this API likely need to FOLL_PIN the page, not just ele= vate + * its refcount. */ -struct page *gfn_to_page(struct kvm *kvm, gfn_t gfn) +struct page *__gfn_to_page(struct kvm *kvm, gfn_t gfn, bool write) { struct page *refcounted_page =3D NULL; struct kvm_follow_pfn kfp =3D { .slot =3D gfn_to_memslot(kvm, gfn), .gfn =3D gfn, - .flags =3D FOLL_WRITE, + .flags =3D write ? FOLL_WRITE : 0, .refcounted_page =3D &refcounted_page, }; =20 (void)kvm_follow_pfn(&kfp); return refcounted_page; } -EXPORT_SYMBOL_GPL(gfn_to_page); +EXPORT_SYMBOL_GPL(__gfn_to_page); =20 int __kvm_vcpu_map(struct kvm_vcpu *vcpu, gfn_t gfn, struct kvm_host_map *= map, bool writable) --=20 2.46.0.rc1.232.g9752f9e123-goog