On 25/11/19 20:00, Sean Christopherson wrote:

[ Upstream commit a78986aae9b2988f8493f9f65a587ee433e83bc3 ]

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 [sean: backport to 4.x; resolve conflict in mmu.c] Signed-off-by: Sean Christopherson sean.j.christopherson@intel.com

---

arch/x86/kvm/mmu.c | 8 ++++---- include/linux/kvm_host.h | 1 + virt/kvm/kvm_main.c | 26 +++++++++++++++++++++++--- 3 files changed, 28 insertions(+), 7 deletions(-)

diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c index f0f180158c26..3a281a2decde 100644 --- a/arch/x86/kvm/mmu.c +++ b/arch/x86/kvm/mmu.c @@ -2934,7 +2934,7 @@ static void transparent_hugepage_adjust(struct kvm_vcpu *vcpu, * here. */ if (!is_error_noslot_pfn(pfn) && !kvm_is_reserved_pfn(pfn) &&

•    level == PT_PAGE_TABLE_LEVEL &&
  

•    !kvm_is_zone_device_pfn(pfn) && level == PT_PAGE_TABLE_LEVEL &&
   PageTransCompoundMap(pfn_to_page(pfn)) &&
   !mmu_gfn_lpage_is_disallowed(vcpu, gfn, PT_DIRECTORY_LEVEL)) {
  

  unsigned long mask;

@@ -4890,9 +4890,9 @@ static bool kvm_mmu_zap_collapsible_spte(struct kvm *kvm, * the guest, and the guest page table is using 4K page size * mapping if the indirect sp has level = 1. */

• if (sp->role.direct &&
  

• 	!kvm_is_reserved_pfn(pfn) &&
  

• 	PageTransCompoundMap(pfn_to_page(pfn))) {
  

• if (sp->role.direct && !kvm_is_reserved_pfn(pfn) &&
  

•     !kvm_is_zone_device_pfn(pfn) &&
  

•     PageTransCompoundMap(pfn_to_page(pfn))) {
  drop_spte(kvm, sptep);
  need_tlb_flush = 1;
  goto restart;
  

diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h index 0590e7d47b02..ab90a8541aaa 100644 --- a/include/linux/kvm_host.h +++ b/include/linux/kvm_host.h @@ -843,6 +843,7 @@ int kvm_cpu_has_pending_timer(struct kvm_vcpu *vcpu); void kvm_vcpu_kick(struct kvm_vcpu *vcpu); bool kvm_is_reserved_pfn(kvm_pfn_t pfn); +bool kvm_is_zone_device_pfn(kvm_pfn_t pfn); struct kvm_irq_ack_notifier { struct hlist_node link; diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c index 0fc93519e63e..c0dff5337a50 100644 --- a/virt/kvm/kvm_main.c +++ b/virt/kvm/kvm_main.c @@ -131,10 +131,30 @@ __weak void kvm_arch_mmu_notifier_invalidate_range(struct kvm *kvm, { } +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; } @@ -1758,7 +1778,7 @@ static void kvm_release_pfn_dirty(kvm_pfn_t pfn) 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);

if (!PageReserved(page)) @@ -1769,7 +1789,7 @@ 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)) mark_page_accessed(pfn_to_page(pfn));

} EXPORT_SYMBOL_GPL(kvm_set_pfn_accessed);

Acked-by: Paolo Bonzini pbonzini@redhat.com