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Subject[PATCH] KVM: x86/mmu: Don't rebuild page when the page is synced and no tlb flushing is required
Date
Before Commit c3e5e415bc1e6 ("KVM: X86: Change kvm_sync_page()
to return true when remote flush is needed"), the return value
of kvm_sync_page() indicates whether the page is synced, and
kvm_mmu_get_page() would rebuild page when the sync fails.
But now, kvm_sync_page() returns false when the page is
synced and no tlb flushing is required, which leads to
rebuild page in kvm_mmu_get_page(). So return the return
value of mmu->sync_page() directly and check it in
kvm_mmu_get_page(). If the sync fails, the page will be
zapped and the invalid_list is not empty, so set flush as
true is accepted in mmu_sync_children().

Fixes: c3e5e415bc1e6 ("KVM: X86: Change kvm_sync_page() to return true when remote flush is needed")
Signed-off-by: Hou Wenlong <houwenlong.hwl@antgroup.com>
---
arch/x86/kvm/mmu/mmu.c | 16 ++++++++--------
1 file changed, 8 insertions(+), 8 deletions(-)

diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index 3b8da8b0745e..8efd165ee27c 100644
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -1866,17 +1866,14 @@ static void kvm_mmu_commit_zap_page(struct kvm *kvm,
&(_kvm)->arch.mmu_page_hash[kvm_page_table_hashfn(_gfn)]) \
if ((_sp)->gfn != (_gfn) || (_sp)->role.direct) {} else

-static bool kvm_sync_page(struct kvm_vcpu *vcpu, struct kvm_mmu_page *sp,
+static int kvm_sync_page(struct kvm_vcpu *vcpu, struct kvm_mmu_page *sp,
struct list_head *invalid_list)
{
int ret = vcpu->arch.mmu->sync_page(vcpu, sp);

- if (ret < 0) {
+ if (ret < 0)
kvm_mmu_prepare_zap_page(vcpu->kvm, sp, invalid_list);
- return false;
- }
-
- return !!ret;
+ return ret;
}

static bool kvm_mmu_remote_flush_or_zap(struct kvm *kvm,
@@ -2039,6 +2036,7 @@ static struct kvm_mmu_page *kvm_mmu_get_page(struct kvm_vcpu *vcpu,
struct hlist_head *sp_list;
unsigned quadrant;
struct kvm_mmu_page *sp;
+ int ret;
int collisions = 0;
LIST_HEAD(invalid_list);

@@ -2091,11 +2089,13 @@ static struct kvm_mmu_page *kvm_mmu_get_page(struct kvm_vcpu *vcpu,
* If the sync fails, the page is zapped. If so, break
* in order to rebuild it.
*/
- if (!kvm_sync_page(vcpu, sp, &invalid_list))
+ ret = kvm_sync_page(vcpu, sp, &invalid_list);
+ if (ret < 0)
break;

WARN_ON(!list_empty(&invalid_list));
- kvm_flush_remote_tlbs(vcpu->kvm);
+ if (ret > 0)
+ kvm_flush_remote_tlbs(vcpu->kvm);
}

__clear_sp_write_flooding_count(sp);
--
2.31.1
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