linux-kernel - [PATCH V2] kvm: check tlbs

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Date:   Tue, 15 Dec 2020 22:52:59 +0800
From:   Lai Jiangshan <jiangshanlai@...il.com>
To:     linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Cc:     Paolo Bonzini <pbonzini@...hat.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Lai Jiangshan <laijs@...ux.alibaba.com>, stable@...r.kernel.org
Subject: [PATCH V2] kvm: check tlbs_dirty directly

From: Lai Jiangshan <laijs@...ux.alibaba.com>

In kvm_mmu_notifier_invalidate_range_start(), tlbs_dirty is used as:
        need_tlb_flush |= kvm->tlbs_dirty;
with need_tlb_flush's type being int and tlbs_dirty's type being long.

It means that tlbs_dirty is always used as int and the higher 32 bits
is useless.  We need to check tlbs_dirty in a correct way and this
change checks it directly without propagating it to need_tlb_flush.

And need_tlb_flush is changed to boolean because it is used as a
boolean and its name starts with "need".

Note: it's _extremely_ unlikely this neglecting of higher 32 bits can
cause problems in practice.  It would require encountering tlbs_dirty
on a 4 billion count boundary, and KVM would need to be using shadow
paging or be running a nested guest.

Cc: stable@...r.kernel.org
Fixes: a4ee1ca4a36e ("KVM: MMU: delay flush all tlbs on sync_page path")
Signed-off-by: Lai Jiangshan <laijs@...ux.alibaba.com>
---
Changed from V1:
	Update the patch and the changelog as Sean Christopherson suggested.

 virt/kvm/kvm_main.c | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 2541a17ff1c4..1c17f3d073cb 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -470,7 +470,8 @@ static int kvm_mmu_notifier_invalidate_range_start(struct mmu_notifier *mn,
 					const struct mmu_notifier_range *range)
 {
 	struct kvm *kvm = mmu_notifier_to_kvm(mn);
-	int need_tlb_flush = 0, idx;
+	int idx;
+	bool need_tlb_flush;
 
 	idx = srcu_read_lock(&kvm->srcu);
 	spin_lock(&kvm->mmu_lock);
@@ -480,11 +481,10 @@ static int kvm_mmu_notifier_invalidate_range_start(struct mmu_notifier *mn,
 	 * count is also read inside the mmu_lock critical section.
 	 */
 	kvm->mmu_notifier_count++;
-	need_tlb_flush = kvm_unmap_hva_range(kvm, range->start, range->end,
-					     range->flags);
-	need_tlb_flush |= kvm->tlbs_dirty;
+	need_tlb_flush = !!kvm_unmap_hva_range(kvm, range->start, range->end,
+					       range->flags);
 	/* we've to flush the tlb before the pages can be freed */
-	if (need_tlb_flush)
+	if (need_tlb_flush || kvm->tlbs_dirty)
 		kvm_flush_remote_tlbs(kvm);
 
 	spin_unlock(&kvm->mmu_lock);
-- 
2.19.1.6.gb485710b