linux-kernel - [PATCH 2/3] kvm: x86/mmu: Ensure TDP MMU roots are freed after yield

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Message-Id: <20210105233136.2140335-2-bgardon@google.com>
Date:   Tue,  5 Jan 2021 15:31:35 -0800
From:   Ben Gardon <bgardon@...gle.com>
To:     linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Cc:     Paolo Bonzini <pbonzini@...hat.com>,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        Peter Shier <pshier@...gle.com>,
        "Maciej S . Szmigiero" <maciej.szmigiero@...cle.com>,
        Leo Hou <leohou1402@...il.com>, Ben Gardon <bgardon@...gle.com>
Subject: [PATCH 2/3] kvm: x86/mmu: Ensure TDP MMU roots are freed after yield

Many TDP MMU functions which need to perform some action on all TDP MMU
roots hold a reference on that root so that they can safely drop the MMU
lock in order to yield to other threads. However, when releasing the
reference on the root, there is a bug: the root will not be freed even
if its reference count (root_count) is reduced to 0. Ensure that these
roots are properly freed.

Reported-by: Maciej S. Szmigiero <maciej.szmigiero@...cle.com>
Fixes: faaf05b00aec ("kvm: x86/mmu: Support zapping SPTEs in the TDP MMU")
Fixes: 063afacd8730 ("kvm: x86/mmu: Support invalidate range MMU notifier for TDP MMU")
Fixes: a6a0b05da9f3 ("kvm: x86/mmu: Support dirty logging for the TDP MMU")
Fixes: 14881998566d ("kvm: x86/mmu: Support disabling dirty logging for the tdp MMU")
Signed-off-by: Ben Gardon <bgardon@...gle.com>
---
 arch/x86/kvm/mmu/tdp_mmu.c | 18 ++++++++++++------
 1 file changed, 12 insertions(+), 6 deletions(-)

diff --git a/arch/x86/kvm/mmu/tdp_mmu.c b/arch/x86/kvm/mmu/tdp_mmu.c
index 75db27fda8f3..5ec6fae36e33 100644
--- a/arch/x86/kvm/mmu/tdp_mmu.c
+++ b/arch/x86/kvm/mmu/tdp_mmu.c
@@ -83,6 +83,12 @@ void kvm_tdp_mmu_free_root(struct kvm *kvm, struct kvm_mmu_page *root)
 	kmem_cache_free(mmu_page_header_cache, root);
 }
 
+static void tdp_mmu_put_root(struct kvm *kvm, struct kvm_mmu_page *root)
+{
+	if (kvm_mmu_put_root(kvm, root))
+		kvm_tdp_mmu_free_root(kvm, root);
+}
+
 static union kvm_mmu_page_role page_role_for_level(struct kvm_vcpu *vcpu,
 						   int level)
 {
@@ -456,7 +462,7 @@ bool kvm_tdp_mmu_zap_gfn_range(struct kvm *kvm, gfn_t start, gfn_t end)
 
 		flush |= zap_gfn_range(kvm, root, start, end, true);
 
-		kvm_mmu_put_root(kvm, root);
+		tdp_mmu_put_root(kvm, root);
 	}
 
 	return flush;
@@ -648,7 +654,7 @@ static int kvm_tdp_mmu_handle_hva_range(struct kvm *kvm, unsigned long start,
 				       gfn_end, data);
 		}
 
-		kvm_mmu_put_root(kvm, root);
+		tdp_mmu_put_root(kvm, root);
 	}
 
 	return ret;
@@ -852,7 +858,7 @@ bool kvm_tdp_mmu_wrprot_slot(struct kvm *kvm, struct kvm_memory_slot *slot,
 		spte_set |= wrprot_gfn_range(kvm, root, slot->base_gfn,
 			     slot->base_gfn + slot->npages, min_level);
 
-		kvm_mmu_put_root(kvm, root);
+		tdp_mmu_put_root(kvm, root);
 	}
 
 	return spte_set;
@@ -920,7 +926,7 @@ bool kvm_tdp_mmu_clear_dirty_slot(struct kvm *kvm, struct kvm_memory_slot *slot)
 		spte_set |= clear_dirty_gfn_range(kvm, root, slot->base_gfn,
 				slot->base_gfn + slot->npages);
 
-		kvm_mmu_put_root(kvm, root);
+		tdp_mmu_put_root(kvm, root);
 	}
 
 	return spte_set;
@@ -1043,7 +1049,7 @@ bool kvm_tdp_mmu_slot_set_dirty(struct kvm *kvm, struct kvm_memory_slot *slot)
 		spte_set |= set_dirty_gfn_range(kvm, root, slot->base_gfn,
 				slot->base_gfn + slot->npages);
 
-		kvm_mmu_put_root(kvm, root);
+		tdp_mmu_put_root(kvm, root);
 	}
 	return spte_set;
 }
@@ -1103,7 +1109,7 @@ void kvm_tdp_mmu_zap_collapsible_sptes(struct kvm *kvm,
 		zap_collapsible_spte_range(kvm, root, slot->base_gfn,
 					   slot->base_gfn + slot->npages);
 
-		kvm_mmu_put_root(kvm, root);
+		tdp_mmu_put_root(kvm, root);
 	}
 }
 
-- 
2.29.2.729.g45daf8777d-goog