[PATCH 5.17 38/75] KVM: x86/mmu: Dont rebuild page when the page is synced and no tlb flushing is required

Greg Kroah-Hartman
2022-06-03T18:09:11Z

From: Hou Wenlong <houwenlong.hwl@antgroup.com>

commit 8d5678a76689acbf91245a3791fe853ab773090f upstream.

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().

Cc: stable@vger.kernel.org
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>
Acked-by: Lai Jiangshan <jiangshanlai@gmail.com>
Message-Id: <0dabeeb789f57b0d793f85d073893063e692032d.1647336064.git.houwenlong.hwl@antgroup.com>
[mmu_sync_children should not flush if the page is zapped. - Paolo]
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
arch/x86/kvm/mmu/mmu.c | 18 +++++++++---------
1 file changed, 9 insertions(+), 9 deletions(-)

--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -1894,17 +1894,14 @@ static void kvm_mmu_commit_zap_page(stru
&(_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,
@@ -2033,7 +2030,7 @@ static int mmu_sync_children(struct kvm_

for_each_sp(pages, sp, parents, i) {
kvm_unlink_unsync_page(vcpu->kvm, sp);
- flush |= kvm_sync_page(vcpu, sp, &invalid_list);
+ flush |= kvm_sync_page(vcpu, sp, &invalid_list) > 0;
mmu_pages_clear_parents(&parents);
}
if (need_resched() || rwlock_needbreak(&vcpu->kvm->mmu_lock)) {
@@ -2074,6 +2071,7 @@ static struct kvm_mmu_page *kvm_mmu_get_
struct hlist_head *sp_list;
unsigned quadrant;
struct kvm_mmu_page *sp;
+ int ret;
int collisions = 0;
LIST_HEAD(invalid_list);

@@ -2126,11 +2124,13 @@ static struct kvm_mmu_page *kvm_mmu_get_
* 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);