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AJvYcCUhMXh4Og+lPQaxKpPmAQl8Y0GbXQnB8lIisVyZzTBjqLzzErhpkpSU1qx0RFU/YSrHilPo4TjUWabRb7pX1rK70sdYq4c9itrOgQ== X-Gm-Message-State: AOJu0YwVc6WPZFFR9ubeXBpjjIw/ZUrlys6oMQEMilaPY5OtKtRRBz2b 6QE3Xz3ewScqU/vRbWsP5v6K6XFGBQqjI+Ia2REbYQNNU11vA/ACwaijM80zm4uvZ45ZqHBnq37 jdg== X-Google-Smtp-Source: AGHT+IGIDN5ccGIB3cs8xyjoNBA33aBwY8OuaAQU+QnM7LAxDHF+KLZuhqGJARF7orYR9wXwPpBL0fgCScs= X-Received: from zagreus.c.googlers.com ([fda3:e722:ac3:cc00:7f:e700:c0a8:5c37]) (user=seanjc job=sendgmr) by 2002:a05:6a00:8593:b0:70d:3466:2f1a with SMTP id d2e1a72fcca58-70ece63fd2emr7784b3a.1.1722038009466; Fri, 26 Jul 2024 16:53:29 -0700 (PDT) Reply-To: Sean Christopherson Date: Fri, 26 Jul 2024 16:51:34 -0700 In-Reply-To: <20240726235234.228822-1-seanjc@google.com> Precedence: bulk X-Mailing-List: linux-mips@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: <20240726235234.228822-26-seanjc@google.com> Subject: [PATCH v12 25/84] KVM: Provide refcounted page as output field in struct kvm_follow_pfn 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 Add kvm_follow_pfn.refcounted_page as an output for the "to pfn" APIs to "return" the struct page that is associated with the returned pfn (if KVM acquired a reference to the page). This will eventually allow removing KVM's hacky kvm_pfn_to_refcounted_page() code, which is error prone and can't detect pfns that are valid, but aren't (currently) refcounted. Signed-off-by: Sean Christopherson --- virt/kvm/kvm_main.c | 100 +++++++++++++++++++++----------------------- virt/kvm/kvm_mm.h | 9 ++++ 2 files changed, 56 insertions(+), 53 deletions(-) diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c index 8e83d3f043f1..31570c5627e3 100644 --- a/virt/kvm/kvm_main.c +++ b/virt/kvm/kvm_main.c @@ -2756,6 +2756,46 @@ static inline int check_user_page_hwpoison(unsigned long addr) return rc == -EHWPOISON; } +static kvm_pfn_t kvm_resolve_pfn(struct kvm_follow_pfn *kfp, struct page *page, + pte_t *pte, bool writable) +{ + kvm_pfn_t pfn; + + WARN_ON_ONCE(!!page == !!pte); + + if (kfp->map_writable) + *kfp->map_writable = writable; + + /* + * FIXME: Remove this once KVM no longer blindly calls put_page() on + * every pfn that points at a struct page. + * + * Get a reference for follow_pte() pfns if they happen to point at a + * struct page, as KVM will ultimately call kvm_release_pfn_clean() on + * the returned pfn, i.e. KVM expects to have a reference. + * + * Certain IO or PFNMAP mappings can be backed with valid struct pages, + * but be allocated without refcounting, e.g. tail pages of + * non-compound higher order allocations. Grabbing and putting a + * reference to such pages would cause KVM to prematurely free a page + * it doesn't own (KVM gets and puts the one and only reference). + * Don't allow those pages until the FIXME is resolved. + */ + if (pte) { + pfn = pte_pfn(*pte); + page = kvm_pfn_to_refcounted_page(pfn); + if (page && !get_page_unless_zero(page)) + return KVM_PFN_ERR_FAULT; + } else { + pfn = page_to_pfn(page); + } + + if (kfp->refcounted_page) + *kfp->refcounted_page = page; + + return pfn; +} + /* * The fast path to get the writable pfn which will be stored in @pfn, * true indicates success, otherwise false is returned. It's also the @@ -2774,9 +2814,7 @@ static bool hva_to_pfn_fast(struct kvm_follow_pfn *kfp, kvm_pfn_t *pfn) return false; if (get_user_page_fast_only(kfp->hva, FOLL_WRITE, &page)) { - *pfn = page_to_pfn(page); - if (kfp->map_writable) - *kfp->map_writable = true; + *pfn = kvm_resolve_pfn(kfp, page, NULL, true); return true; } @@ -2808,23 +2846,15 @@ static int hva_to_pfn_slow(struct kvm_follow_pfn *kfp, kvm_pfn_t *pfn) if (npages != 1) return npages; - if (!kfp->map_writable) - goto out; - - if (kfp->flags & FOLL_WRITE) { - *kfp->map_writable = true; - goto out; - } - /* map read fault as writable if possible */ - if (get_user_page_fast_only(kfp->hva, FOLL_WRITE, &wpage)) { - *kfp->map_writable = true; + if (!(flags & FOLL_WRITE) && kfp->map_writable && + get_user_page_fast_only(kfp->hva, FOLL_WRITE, &wpage)) { put_page(page); page = wpage; + flags |= FOLL_WRITE; } -out: - *pfn = page_to_pfn(page); + *pfn = kvm_resolve_pfn(kfp, page, NULL, flags & FOLL_WRITE); return npages; } @@ -2839,20 +2869,9 @@ static bool vma_is_valid(struct vm_area_struct *vma, bool write_fault) return true; } -static int kvm_try_get_pfn(kvm_pfn_t pfn) -{ - struct page *page = kvm_pfn_to_refcounted_page(pfn); - - if (!page) - return 1; - - return get_page_unless_zero(page); -} - static int hva_to_pfn_remapped(struct vm_area_struct *vma, struct kvm_follow_pfn *kfp, kvm_pfn_t *p_pfn) { - kvm_pfn_t pfn; pte_t *ptep; pte_t pte; spinlock_t *ptl; @@ -2882,38 +2901,13 @@ static int hva_to_pfn_remapped(struct vm_area_struct *vma, pte = ptep_get(ptep); if (write_fault && !pte_write(pte)) { - pfn = KVM_PFN_ERR_RO_FAULT; + *p_pfn = KVM_PFN_ERR_RO_FAULT; goto out; } - if (kfp->map_writable) - *kfp->map_writable = pte_write(pte); - pfn = pte_pfn(pte); - - /* - * Get a reference here because callers of *hva_to_pfn* and - * *gfn_to_pfn* ultimately call kvm_release_pfn_clean on the - * returned pfn. This is only needed if the VMA has VM_MIXEDMAP - * set, but the kvm_try_get_pfn/kvm_release_pfn_clean pair will - * simply do nothing for reserved pfns. - * - * Whoever called remap_pfn_range is also going to call e.g. - * unmap_mapping_range before the underlying pages are freed, - * causing a call to our MMU notifier. - * - * Certain IO or PFNMAP mappings can be backed with valid - * struct pages, but be allocated without refcounting e.g., - * tail pages of non-compound higher order allocations, which - * would then underflow the refcount when the caller does the - * required put_page. Don't allow those pages here. - */ - if (!kvm_try_get_pfn(pfn)) - r = -EFAULT; - + *p_pfn = kvm_resolve_pfn(kfp, NULL, &pte, pte_write(pte)); out: pte_unmap_unlock(ptep, ptl); - *p_pfn = pfn; - return r; } diff --git a/virt/kvm/kvm_mm.h b/virt/kvm/kvm_mm.h index d5a215958f06..d3ac1ba8ba66 100644 --- a/virt/kvm/kvm_mm.h +++ b/virt/kvm/kvm_mm.h @@ -35,6 +35,15 @@ struct kvm_follow_pfn { * Set to true if a writable mapping was obtained. */ bool *map_writable; + + /* + * Optional output. Set to a valid "struct page" if the returned pfn + * is for a refcounted or pinned struct page, NULL if the returned pfn + * has no struct page or if the struct page is not being refcounted + * (e.g. tail pages of non-compound higher order allocations from + * IO/PFNMAP mappings). + */ + struct page **refcounted_page; }; kvm_pfn_t hva_to_pfn(struct kvm_follow_pfn *kfp);