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[5.10/5.11,8/9] KVM: x86/mmu: Don't allow TDP MMU to yield when recovering NX pages

Message ID 20210410151229.4062930-9-pbonzini@redhat.com (mailing list archive)
State New
Headers show
Series Fix missing TLB flushes in TDP MMU | expand

Commit Message

Paolo Bonzini April 10, 2021, 3:12 p.m. UTC
From: Sean Christopherson <seanjc@google.com>

[ Upstream commit 33a3164161fc86b9cc238f7f2aa2ccb1d5559b1c ]

Prevent the TDP MMU from yielding when zapping a gfn range during NX
page recovery.  If a flush is pending from a previous invocation of the
zapping helper, either in the TDP MMU or the legacy MMU, but the TDP MMU
has not accumulated a flush for the current invocation, then yielding
will release mmu_lock with stale TLB entries.

That being said, this isn't technically a bug fix in the current code, as
the TDP MMU will never yield in this case.  tdp_mmu_iter_cond_resched()
will yield if and only if it has made forward progress, as defined by the
current gfn vs. the last yielded (or starting) gfn.  Because zapping a
single shadow page is guaranteed to (a) find that page and (b) step
sideways at the level of the shadow page, the TDP iter will break its loop
before getting a chance to yield.

But that is all very, very subtle, and will break at the slightest sneeze,
e.g. zapping while holding mmu_lock for read would break as the TDP MMU
wouldn't be guaranteed to see the present shadow page, and thus could step
sideways at a lower level.

Cc: Ben Gardon <bgardon@google.com>
Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20210325200119.1359384-4-seanjc@google.com>
[Add lockdep assertion. - Paolo]
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
 arch/x86/kvm/mmu/mmu.c     |  6 ++----
 arch/x86/kvm/mmu/tdp_mmu.c |  5 +++--
 arch/x86/kvm/mmu/tdp_mmu.h | 18 +++++++++++++++++-
 3 files changed, 22 insertions(+), 7 deletions(-)
diff mbox series


diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index 64ac8ae4f7a1..387dca3f81cd 100644
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -5986,7 +5986,6 @@  static void kvm_recover_nx_lpages(struct kvm *kvm)
 	unsigned int ratio;
 	bool flush = false;
-	gfn_t gfn_end;
 	ulong to_zap;
 	rcu_idx = srcu_read_lock(&kvm->srcu);
@@ -6007,9 +6006,8 @@  static void kvm_recover_nx_lpages(struct kvm *kvm)
 				      struct kvm_mmu_page,
-		if (sp->tdp_mmu_page)
-			gfn_end = sp->gfn + KVM_PAGES_PER_HPAGE(sp->role.level);
-			flush = kvm_tdp_mmu_zap_gfn_range(kvm, sp->gfn, gfn_end);
+		if (sp->tdp_mmu_page) {
+			flush = kvm_tdp_mmu_zap_sp(kvm, sp);
 		} else {
 			kvm_mmu_prepare_zap_page(kvm, sp, &invalid_list);
diff --git a/arch/x86/kvm/mmu/tdp_mmu.c b/arch/x86/kvm/mmu/tdp_mmu.c
index 0bb62b89476a..a16559f31d94 100644
--- a/arch/x86/kvm/mmu/tdp_mmu.c
+++ b/arch/x86/kvm/mmu/tdp_mmu.c
@@ -503,13 +503,14 @@  static bool zap_gfn_range(struct kvm *kvm, struct kvm_mmu_page *root,
  * SPTEs have been cleared and a TLB flush is needed before releasing the
  * MMU lock.
-bool kvm_tdp_mmu_zap_gfn_range(struct kvm *kvm, gfn_t start, gfn_t end)
+bool __kvm_tdp_mmu_zap_gfn_range(struct kvm *kvm, gfn_t start, gfn_t end,
+				 bool can_yield)
 	struct kvm_mmu_page *root;
 	bool flush = false;
 	for_each_tdp_mmu_root_yield_safe(kvm, root)
-		flush = zap_gfn_range(kvm, root, start, end, true, flush);
+		flush = zap_gfn_range(kvm, root, start, end, can_yield, flush);
 	return flush;
diff --git a/arch/x86/kvm/mmu/tdp_mmu.h b/arch/x86/kvm/mmu/tdp_mmu.h
index cbbdbadd1526..a7a3f6db263d 100644
--- a/arch/x86/kvm/mmu/tdp_mmu.h
+++ b/arch/x86/kvm/mmu/tdp_mmu.h
@@ -12,7 +12,23 @@  bool is_tdp_mmu_root(struct kvm *kvm, hpa_t root);
 hpa_t kvm_tdp_mmu_get_vcpu_root_hpa(struct kvm_vcpu *vcpu);
 void kvm_tdp_mmu_free_root(struct kvm *kvm, struct kvm_mmu_page *root);
-bool kvm_tdp_mmu_zap_gfn_range(struct kvm *kvm, gfn_t start, gfn_t end);
+bool __kvm_tdp_mmu_zap_gfn_range(struct kvm *kvm, gfn_t start, gfn_t end,
+				 bool can_yield);
+static inline bool kvm_tdp_mmu_zap_gfn_range(struct kvm *kvm, gfn_t start,
+					     gfn_t end)
+	return __kvm_tdp_mmu_zap_gfn_range(kvm, start, end, true);
+static inline bool kvm_tdp_mmu_zap_sp(struct kvm *kvm, struct kvm_mmu_page *sp)
+	gfn_t end = sp->gfn + KVM_PAGES_PER_HPAGE(sp->role.level);
+	/*
+	 * Don't allow yielding, as the caller may have pending pages to zap
+	 * on the shadow MMU.
+	 */
+	return __kvm_tdp_mmu_zap_gfn_range(kvm, sp->gfn, end, false);
 void kvm_tdp_mmu_zap_all(struct kvm *kvm);
 int kvm_tdp_mmu_map(struct kvm_vcpu *vcpu, gpa_t gpa, u32 error_code,