path: root/virt
diff options
authorSean Christopherson <sean.j.christopherson@intel.com>2019-11-11 14:12:27 -0800
committerPaolo Bonzini <pbonzini@redhat.com>2019-11-12 10:17:42 +0100
commita78986aae9b2988f8493f9f65a587ee433e83bc3 (patch)
treea630d421bde6adbf63834c840e3276096ecae4b1 /virt
parentKVM: VMX: Introduce pi_is_pir_empty() helper (diff)
KVM: MMU: Do not treat ZONE_DEVICE pages as being reserved
Explicitly exempt ZONE_DEVICE pages from kvm_is_reserved_pfn() and instead manually handle ZONE_DEVICE on a case-by-case basis. For things like page refcounts, KVM needs to treat ZONE_DEVICE pages like normal pages, e.g. put pages grabbed via gup(). But for flows such as setting A/D bits or shifting refcounts for transparent huge pages, KVM needs to to avoid processing ZONE_DEVICE pages as the flows in question lack the underlying machinery for proper handling of ZONE_DEVICE pages. This fixes a hang reported by Adam Borowski[*] in dev_pagemap_cleanup() when running a KVM guest backed with /dev/dax memory, as KVM straight up doesn't put any references to ZONE_DEVICE pages acquired by gup(). Note, Dan Williams proposed an alternative solution of doing put_page() on ZONE_DEVICE pages immediately after gup() in order to simplify the auditing needed to ensure is_zone_device_page() is called if and only if the backing device is pinned (via gup()). But that approach would break kvm_vcpu_{un}map() as KVM requires the page to be pinned from map() 'til unmap() when accessing guest memory, unlike KVM's secondary MMU, which coordinates with mmu_notifier invalidations to avoid creating stale page references, i.e. doesn't rely on pages being pinned. [*] http://lkml.kernel.org/r/20190919115547.GA17963@angband.pl Reported-by: Adam Borowski <kilobyte@angband.pl> Analyzed-by: David Hildenbrand <david@redhat.com> Acked-by: Dan Williams <dan.j.williams@intel.com> Cc: stable@vger.kernel.org Fixes: 3565fce3a659 ("mm, x86: get_user_pages() for dax mappings") Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Diffstat (limited to 'virt')
1 files changed, 23 insertions, 3 deletions
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index e7a07132cd7f..0dac149ead16 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -149,10 +149,30 @@ __weak int kvm_arch_mmu_notifier_invalidate_range(struct kvm *kvm,
return 0;
+bool kvm_is_zone_device_pfn(kvm_pfn_t pfn)
+ /*
+ * The metadata used by is_zone_device_page() to determine whether or
+ * not a page is ZONE_DEVICE is guaranteed to be valid if and only if
+ * the device has been pinned, e.g. by get_user_pages(). WARN if the
+ * page_count() is zero to help detect bad usage of this helper.
+ */
+ if (!pfn_valid(pfn) || WARN_ON_ONCE(!page_count(pfn_to_page(pfn))))
+ return false;
+ return is_zone_device_page(pfn_to_page(pfn));
bool kvm_is_reserved_pfn(kvm_pfn_t pfn)
+ /*
+ * ZONE_DEVICE pages currently set PG_reserved, but from a refcounting
+ * perspective they are "normal" pages, albeit with slightly different
+ * usage rules.
+ */
if (pfn_valid(pfn))
- return PageReserved(pfn_to_page(pfn));
+ return PageReserved(pfn_to_page(pfn)) &&
+ !kvm_is_zone_device_pfn(pfn);
return true;
@@ -1857,7 +1877,7 @@ EXPORT_SYMBOL_GPL(kvm_release_pfn_dirty);
void kvm_set_pfn_dirty(kvm_pfn_t pfn)
- if (!kvm_is_reserved_pfn(pfn)) {
+ if (!kvm_is_reserved_pfn(pfn) && !kvm_is_zone_device_pfn(pfn)) {
struct page *page = pfn_to_page(pfn);
@@ -1867,7 +1887,7 @@ EXPORT_SYMBOL_GPL(kvm_set_pfn_dirty);
void kvm_set_pfn_accessed(kvm_pfn_t pfn)
- if (!kvm_is_reserved_pfn(pfn))
+ if (!kvm_is_reserved_pfn(pfn) && !kvm_is_zone_device_pfn(pfn))