diff options
Diffstat (limited to 'virt')
| -rw-r--r-- | virt/kvm/kvm_main.c | 54 | ||||
| -rw-r--r-- | virt/kvm/kvm_mm.h | 7 |
2 files changed, 46 insertions, 15 deletions
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c index 842a5d5f3120..0d59f47f099e 100644 --- a/virt/kvm/kvm_main.c +++ b/virt/kvm/kvm_main.c @@ -2814,9 +2814,12 @@ static kvm_pfn_t kvm_resolve_pfn(struct kvm_follow_pfn *kfp, struct page *page, */ if (map) { pfn = map->pfn; - page = kvm_pfn_to_refcounted_page(pfn); - if (page && !get_page_unless_zero(page)) - return KVM_PFN_ERR_FAULT; + + if (!kfp->pin) { + 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); } @@ -2834,16 +2837,24 @@ static kvm_pfn_t kvm_resolve_pfn(struct kvm_follow_pfn *kfp, struct page *page, static bool hva_to_pfn_fast(struct kvm_follow_pfn *kfp, kvm_pfn_t *pfn) { struct page *page; + bool r; /* - * Fast pin a writable pfn only if it is a write fault request - * or the caller allows to map a writable pfn for a read fault - * request. + * Try the fast-only path when the caller wants to pin/get the page for + * writing. If the caller only wants to read the page, KVM must go + * down the full, slow path in order to avoid racing an operation that + * breaks Copy-on-Write (CoW), e.g. so that KVM doesn't end up pointing + * at the old, read-only page while mm/ points at a new, writable page. */ if (!((kfp->flags & FOLL_WRITE) || kfp->map_writable)) return false; - if (get_user_page_fast_only(kfp->hva, FOLL_WRITE, &page)) { + if (kfp->pin) + r = pin_user_pages_fast(kfp->hva, 1, FOLL_WRITE, &page) == 1; + else + r = get_user_page_fast_only(kfp->hva, FOLL_WRITE, &page); + + if (r) { *pfn = kvm_resolve_pfn(kfp, page, NULL, true); return true; } @@ -2872,10 +2883,21 @@ static int hva_to_pfn_slow(struct kvm_follow_pfn *kfp, kvm_pfn_t *pfn) struct page *page, *wpage; int npages; - npages = get_user_pages_unlocked(kfp->hva, 1, &page, flags); + if (kfp->pin) + npages = pin_user_pages_unlocked(kfp->hva, 1, &page, flags); + else + npages = get_user_pages_unlocked(kfp->hva, 1, &page, flags); if (npages != 1) return npages; + /* + * Pinning is mutually exclusive with opportunistically mapping a read + * fault as writable, as KVM should never pin pages when mapping memory + * into the guest (pinning is only for direct accesses from KVM). + */ + if (WARN_ON_ONCE(kfp->map_writable && kfp->pin)) + goto out; + /* map read fault as writable if possible */ if (!(flags & FOLL_WRITE) && kfp->map_writable && get_user_page_fast_only(kfp->hva, FOLL_WRITE, &wpage)) { @@ -2884,6 +2906,7 @@ static int hva_to_pfn_slow(struct kvm_follow_pfn *kfp, kvm_pfn_t *pfn) flags |= FOLL_WRITE; } +out: *pfn = kvm_resolve_pfn(kfp, page, NULL, flags & FOLL_WRITE); return npages; } @@ -3093,10 +3116,11 @@ int kvm_vcpu_map(struct kvm_vcpu *vcpu, gfn_t gfn, struct kvm_host_map *map) .slot = gfn_to_memslot(vcpu->kvm, gfn), .gfn = gfn, .flags = FOLL_WRITE, - .refcounted_page = &map->refcounted_page, + .refcounted_page = &map->pinned_page, + .pin = true, }; - map->refcounted_page = NULL; + map->pinned_page = NULL; map->page = NULL; map->hva = NULL; map->gfn = gfn; @@ -3133,16 +3157,16 @@ void kvm_vcpu_unmap(struct kvm_vcpu *vcpu, struct kvm_host_map *map, bool dirty) if (dirty) kvm_vcpu_mark_page_dirty(vcpu, map->gfn); - if (map->refcounted_page) { + if (map->pinned_page) { if (dirty) - kvm_release_page_dirty(map->refcounted_page); - else - kvm_release_page_clean(map->refcounted_page); + kvm_set_page_dirty(map->pinned_page); + kvm_set_page_accessed(map->pinned_page); + unpin_user_page(map->pinned_page); } map->hva = NULL; map->page = NULL; - map->refcounted_page = NULL; + map->pinned_page = NULL; } EXPORT_SYMBOL_GPL(kvm_vcpu_unmap); diff --git a/virt/kvm/kvm_mm.h b/virt/kvm/kvm_mm.h index d3ac1ba8ba66..acef3f5c582a 100644 --- a/virt/kvm/kvm_mm.h +++ b/virt/kvm/kvm_mm.h @@ -31,6 +31,13 @@ struct kvm_follow_pfn { unsigned int flags; /* + * Pin the page (effectively FOLL_PIN, which is an mm/ internal flag). + * The page *must* be pinned if KVM will write to the page via a kernel + * mapping, e.g. via kmap(), mremap(), etc. + */ + bool pin; + + /* * If non-NULL, try to get a writable mapping even for a read fault. * Set to true if a writable mapping was obtained. */ |