diff options
Diffstat (limited to 'virt')
| -rw-r--r-- | virt/kvm/kvm_main.c | 99 | ||||
| -rw-r--r-- | virt/kvm/kvm_mm.h | 9 |
2 files changed, 56 insertions, 52 deletions
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c index 32f0858da7f2..b3b4b374dddc 100644 --- a/virt/kvm/kvm_main.c +++ b/virt/kvm/kvm_main.c @@ -2746,6 +2746,46 @@ unsigned long kvm_vcpu_gfn_to_hva_prot(struct kvm_vcpu *vcpu, gfn_t gfn, bool *w return gfn_to_hva_memslot_prot(slot, gfn, writable); } +static kvm_pfn_t kvm_resolve_pfn(struct kvm_follow_pfn *kfp, struct page *page, + struct follow_pfnmap_args *map, bool writable) +{ + kvm_pfn_t pfn; + + WARN_ON_ONCE(!!page == !!map); + + 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 (map) { + pfn = map->pfn; + 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. @@ -2763,9 +2803,7 @@ 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; } @@ -2797,23 +2835,15 @@ 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; } @@ -2828,22 +2858,11 @@ 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) { struct follow_pfnmap_args args = { .vma = vma, .address = kfp->hva }; bool write_fault = kfp->flags & FOLL_WRITE; - kvm_pfn_t pfn; int r; r = follow_pfnmap_start(&args); @@ -2867,37 +2886,13 @@ static int hva_to_pfn_remapped(struct vm_area_struct *vma, } if (write_fault && !args.writable) { - pfn = KVM_PFN_ERR_RO_FAULT; + *p_pfn = KVM_PFN_ERR_RO_FAULT; goto out; } - if (kfp->map_writable) - *kfp->map_writable = args.writable; - pfn = args.pfn; - - /* - * 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, &args, args.writable); out: follow_pfnmap_end(&args); - *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); |