[PATCH 5.10/5.11 6/9] KVM: x86/mmu: Ensure TLBs are flushed when yielding during GFN range zap

[Paolo Bonzini <pbonzini@xxxxxxxxxx>]

From: Sean Christopherson <seanjc@xxxxxxxxxx>

[ Upstream commit a835429cda91621fca915d80672a157b47738afb ]

When flushing a range of GFNs across multiple roots, ensure any pending
flush from a previous root is honored before yielding while walking the
tables of the current root.

Note, kvm_tdp_mmu_zap_gfn_range() now intentionally overwrites its local
"flush" with the result to avoid redundant flushes.  zap_gfn_range()
preserves and return the incoming "flush", unless of course the flush was
performed prior to yielding and no new flush was triggered.

Fixes: 1af4a96025b3 ("KVM: x86/mmu: Yield in TDU MMU iter even if no SPTES changed")
Cc: stable@xxxxxxxxxxxxxxx
Reviewed-by: Ben Gardon <bgardon@xxxxxxxxxx>
Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx>
Message-Id: <20210325200119.1359384-2-seanjc@xxxxxxxxxx>
Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
---
 arch/x86/kvm/mmu/tdp_mmu.c | 24 +++++++++++++-----------
 1 file changed, 13 insertions(+), 11 deletions(-)

diff --git a/arch/x86/kvm/mmu/tdp_mmu.c b/arch/x86/kvm/mmu/tdp_mmu.c
index 0567286fba39..0bb62b89476a 100644
--- a/arch/x86/kvm/mmu/tdp_mmu.c
+++ b/arch/x86/kvm/mmu/tdp_mmu.c
@@ -105,7 +105,7 @@ bool is_tdp_mmu_root(struct kvm *kvm, hpa_t hpa)
 }
 
 static bool zap_gfn_range(struct kvm *kvm, struct kvm_mmu_page *root,
-			  gfn_t start, gfn_t end, bool can_yield);
+			  gfn_t start, gfn_t end, bool can_yield, bool flush);
 
 void kvm_tdp_mmu_free_root(struct kvm *kvm, struct kvm_mmu_page *root)
 {
@@ -118,7 +118,7 @@ void kvm_tdp_mmu_free_root(struct kvm *kvm, struct kvm_mmu_page *root)
 
 	list_del(&root->link);
 
-	zap_gfn_range(kvm, root, 0, max_gfn, false);
+	zap_gfn_range(kvm, root, 0, max_gfn, false, false);
 
 	free_page((unsigned long)root->spt);
 	kmem_cache_free(mmu_page_header_cache, root);
@@ -461,18 +461,19 @@ static inline bool tdp_mmu_iter_cond_resched(struct kvm *kvm,
  * scheduler needs the CPU or there is contention on the MMU lock. If this
  * function cannot yield, it will not release the MMU lock or reschedule and
  * the caller must ensure it does not supply too large a GFN range, or the
- * operation can cause a soft lockup.
+ * operation can cause a soft lockup.  Note, in some use cases a flush may be
+ * required by prior actions.  Ensure the pending flush is performed prior to
+ * yielding.
  */
 static bool zap_gfn_range(struct kvm *kvm, struct kvm_mmu_page *root,
-			  gfn_t start, gfn_t end, bool can_yield)
+			  gfn_t start, gfn_t end, bool can_yield, bool flush)
 {
 	struct tdp_iter iter;
-	bool flush_needed = false;
 
 	tdp_root_for_each_pte(iter, root, start, end) {
 		if (can_yield &&
-		    tdp_mmu_iter_cond_resched(kvm, &iter, flush_needed)) {
-			flush_needed = false;
+		    tdp_mmu_iter_cond_resched(kvm, &iter, flush)) {
+			flush = false;
 			continue;
 		}
 
@@ -490,9 +491,10 @@ static bool zap_gfn_range(struct kvm *kvm, struct kvm_mmu_page *root,
 			continue;
 
 		tdp_mmu_set_spte(kvm, &iter, 0);
-		flush_needed = true;
+		flush = true;
 	}
-	return flush_needed;
+
+	return flush;
 }
 
 /*
@@ -507,7 +509,7 @@ bool kvm_tdp_mmu_zap_gfn_range(struct kvm *kvm, gfn_t start, gfn_t end)
 	bool flush = false;
 
 	for_each_tdp_mmu_root_yield_safe(kvm, root)
-		flush |= zap_gfn_range(kvm, root, start, end, true);
+		flush = zap_gfn_range(kvm, root, start, end, true, flush);
 
 	return flush;
 }
@@ -701,7 +703,7 @@ static int zap_gfn_range_hva_wrapper(struct kvm *kvm,
 				     struct kvm_mmu_page *root, gfn_t start,
 				     gfn_t end, unsigned long unused)
 {
-	return zap_gfn_range(kvm, root, start, end, false);
+	return zap_gfn_range(kvm, root, start, end, false, false);
 }
 
 int kvm_tdp_mmu_zap_hva_range(struct kvm *kvm, unsigned long start,
-- 
2.26.2