[PATCH V2 06/10] KVM: X86: Change kvm_sync_page() to return true when remote flush is needed

Lai Jiangshan
2021-09-18T00:57:21Z

Currently kvm_sync_page() returns true when there is any present spte.
But the return value is ignored in the callers.

Changing kvm_sync_page() to return true when remote flush is needed and
changing mmu->sync_page() not to directly flush can combine and reduce
remote flush requests.

Signed-off-by: Lai Jiangshan <laijs@linux.alibaba.com>
---
arch/x86/kvm/mmu/mmu.c | 21 +++++++++++++--------
arch/x86/kvm/mmu/paging_tmpl.h | 21 ++++++++++-----------
2 files changed, 23 insertions(+), 19 deletions(-)

diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index 9aba5d93a747..2f3f47dc96b0 100644
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -1792,7 +1792,7 @@ static void mark_unsync(u64 *spte)
static int nonpaging_sync_page(struct kvm_vcpu *vcpu,
struct kvm_mmu_page *sp)
{
- return 0;
+ return -1;
}

#define KVM_PAGE_ARRAY_NR 16
@@ -1906,12 +1906,14 @@ static void kvm_mmu_commit_zap_page(struct kvm *kvm,
static bool kvm_sync_page(struct kvm_vcpu *vcpu, struct kvm_mmu_page *sp,
struct list_head *invalid_list)
{
- if (vcpu->arch.mmu->sync_page(vcpu, sp) == 0) {
+ int ret = vcpu->arch.mmu->sync_page(vcpu, sp);
+
+ if (ret < 0) {
kvm_mmu_prepare_zap_page(vcpu->kvm, sp, invalid_list);
return false;
}

- return true;
+ return !!ret;
}

static bool kvm_mmu_remote_flush_or_zap(struct kvm *kvm,
@@ -2021,6 +2023,7 @@ static int mmu_sync_children(struct kvm_vcpu *vcpu,
struct mmu_page_path parents;
struct kvm_mmu_pages pages;
LIST_HEAD(invalid_list);
+ bool flush = false;

while (mmu_unsync_walk(parent, &pages)) {
bool protected = false;
@@ -2030,23 +2033,25 @@ static int mmu_sync_children(struct kvm_vcpu *vcpu,

if (protected) {
kvm_flush_remote_tlbs(vcpu->kvm);
+ flush = false;
}

for_each_sp(pages, sp, parents, i) {
kvm_unlink_unsync_page(vcpu->kvm, sp);
- kvm_sync_page(vcpu, sp, &invalid_list);
+ flush |= kvm_sync_page(vcpu, sp, &invalid_list);
mmu_pages_clear_parents(&parents);
}
if (need_resched() || rwlock_needbreak(&vcpu->kvm->mmu_lock)) {
- kvm_mmu_remote_flush_or_zap(vcpu->kvm, &invalid_list, false);
+ kvm_mmu_remote_flush_or_zap(vcpu->kvm, &invalid_list, flush);
if (!can_yield)
return -EINTR;

cond_resched_rwlock_write(&vcpu->kvm->mmu_lock);
+ flush = false;
}
}

- kvm_mmu_remote_flush_or_zap(vcpu->kvm, &invalid_list, false);
+ kvm_mmu_remote_flush_or_zap(vcpu->kvm, &invalid_list, flush);
return 0;
}

@@ -2130,6 +2135,7 @@ static struct kvm_mmu_page *kvm_mmu_get_page(struct kvm_vcpu *vcpu,
break;

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

__clear_sp_write_flooding_count(sp);
@@ -4128,7 +4134,7 @@ static unsigned long get_cr3(struct kvm_vcpu *vcpu)
}

static bool sync_mmio_spte(struct kvm_vcpu *vcpu, u64 *sptep, gfn_t gfn,
- unsigned int access, int *nr_present)
+ unsigned int access)
{
if (unlikely(is_mmio_spte(*sptep))) {
if (gfn != get_mmio_spte_gfn(*sptep)) {
@@ -4136,7 +4142,6 @@ static bool sync_mmio_spte(struct kvm_vcpu *vcpu, u64 *sptep, gfn_t gfn,
return true;
}

- (*nr_present)++;
mark_mmio_spte(vcpu, sptep, gfn, access);
return true;
}
diff --git a/arch/x86/kvm/mmu/paging_tmpl.h b/arch/x86/kvm/mmu/paging_tmpl.h
index 87374cfd82be..c3edbc0f06b3 100644
--- a/arch/x86/kvm/mmu/paging_tmpl.h
+++ b/arch/x86/kvm/mmu/paging_tmpl.h
@@ -1060,11 +1060,16 @@ static gpa_t FNAME(gva_to_gpa_nested)(struct kvm_vcpu *vcpu, gpa_t vaddr,
* Using the cached information from sp->gfns is safe because:
* - The spte has a reference to the struct page, so the pfn for a given gfn
* can't change unless all sptes pointing to it are nuked first.
+ *
+ * Returns
+ * < 0: the sp should be zapped
+ * 0: the sp is synced and no tlb flushing is required
+ * > 0: the sp is synced and tlb flushing is required
*/
static int FNAME(sync_page)(struct kvm_vcpu *vcpu, struct kvm_mmu_page *sp)
{
union kvm_mmu_page_role mmu_role = vcpu->arch.mmu->mmu_role.base;
- int i, nr_present = 0;
+ int i;
bool host_writable;
gpa_t first_pte_gpa;
int set_spte_ret = 0;
@@ -1092,7 +1097,7 @@ static int FNAME(sync_page)(struct kvm_vcpu *vcpu, struct kvm_mmu_page *sp)
*/
if (WARN_ON_ONCE(sp->role.direct ||
(sp->role.word ^ mmu_role.word) & ~sync_role_ign.word))
- return 0;
+ return -1;

first_pte_gpa = FNAME(get_level1_sp_gpa)(sp);

@@ -1109,7 +1114,7 @@ static int FNAME(sync_page)(struct kvm_vcpu *vcpu, struct kvm_mmu_page *sp)

if (kvm_vcpu_read_guest_atomic(vcpu, pte_gpa, &gpte,
sizeof(pt_element_t)))
- return 0;
+ return -1;

if (FNAME(prefetch_invalid_gpte)(vcpu, sp, &sp->spt[i], gpte)) {
set_spte_ret |= SET_SPTE_NEED_REMOTE_TLB_FLUSH;
@@ -1121,8 +1126,7 @@ static int FNAME(sync_page)(struct kvm_vcpu *vcpu, struct kvm_mmu_page *sp)
pte_access &= FNAME(gpte_access)(gpte);
FNAME(protect_clean_gpte)(vcpu->arch.mmu, &pte_access, gpte);

- if (sync_mmio_spte(vcpu, &sp->spt[i], gfn, pte_access,
- &nr_present))
+ if (sync_mmio_spte(vcpu, &sp->spt[i], gfn, pte_access))
continue;

if (gfn != sp->gfns[i]) {
@@ -1131,8 +1135,6 @@ static int FNAME(sync_page)(struct kvm_vcpu *vcpu, struct kvm_mmu_page *sp)
continue;
}

- nr_present++;
-
host_writable = sp->spt[i] & shadow_host_writable_mask;

set_spte_ret |= set_spte(vcpu, &sp->spt[i],
@@ -1141,10 +1143,7 @@ static int FNAME(sync_page)(struct kvm_vcpu *vcpu, struct kvm_mmu_page *sp)
true, false, host_writable);
}

- if (set_spte_ret & SET_SPTE_NEED_REMOTE_TLB_FLUSH)
- kvm_flush_remote_tlbs(vcpu->kvm);
-
- return nr_present;
+ return set_spte_ret & SET_SPTE_NEED_REMOTE_TLB_FLUSH;
}

#undef pt_element_t
--
2.19.1.6.gb485710b