linux-kernel - [PATCH 5.4 77/92] kvm: check tlbs

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Date:   Mon, 11 Jan 2021 14:02:21 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Lai Jiangshan <laijs@...ux.alibaba.com>,
        Paolo Bonzini <pbonzini@...hat.com>
Subject: [PATCH 5.4 77/92] kvm: check tlbs_dirty directly

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

commit 88bf56d04bc3564542049ec4ec168a8b60d0b48c upstream.

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.

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>
Message-Id: <20201217154118.16497-1-jiangshanlai@...il.com>
Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 virt/kvm/kvm_main.c |    3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -428,9 +428,8 @@ static int kvm_mmu_notifier_invalidate_r
 	kvm->mmu_notifier_count++;
 	need_tlb_flush = kvm_unmap_hva_range(kvm, range->start, range->end,
 					     range->flags);
-	need_tlb_flush |= kvm->tlbs_dirty;
 	/* 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);