[PATCH V2 09/10] KVM: X86: Don't unsync pagetables when speculative

Lai Jiangshan
2021-09-18T00:57:36Z

We'd better only unsync the pagetable when there just was a really
write fault on a level-1 pagetable.

Signed-off-by: Lai Jiangshan <laijs@linux.alibaba.com>
---
arch/x86/kvm/mmu/mmu.c | 6 +++++-
arch/x86/kvm/mmu/mmu_internal.h | 3 ++-
arch/x86/kvm/mmu/spte.c | 2 +-
3 files changed, 8 insertions(+), 3 deletions(-)

diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index ff52e8354148..e3213d804647 100644
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -2577,7 +2577,8 @@ static void kvm_unsync_page(struct kvm_vcpu *vcpu, struct kvm_mmu_page *sp)
* were marked unsync (or if there is no shadow page), -EPERM if the SPTE must
* be write-protected.
*/
-int mmu_try_to_unsync_pages(struct kvm_vcpu *vcpu, gfn_t gfn, bool can_unsync)
+int mmu_try_to_unsync_pages(struct kvm_vcpu *vcpu, gfn_t gfn, bool can_unsync,
+ bool speculative)
{
struct kvm_mmu_page *sp;
bool locked = false;
@@ -2603,6 +2604,9 @@ int mmu_try_to_unsync_pages(struct kvm_vcpu *vcpu, gfn_t gfn, bool can_unsync)
if (sp->unsync)
continue;

+ if (speculative)
+ return -EEXIST;
+
/*
* TDP MMU page faults require an additional spinlock as they
* run with mmu_lock held for read, not write, and the unsync
diff --git a/arch/x86/kvm/mmu/mmu_internal.h b/arch/x86/kvm/mmu/mmu_internal.h
index 658d8d228d43..f5d8be787993 100644
--- a/arch/x86/kvm/mmu/mmu_internal.h
+++ b/arch/x86/kvm/mmu/mmu_internal.h
@@ -116,7 +116,8 @@ static inline bool kvm_vcpu_ad_need_write_protect(struct kvm_vcpu *vcpu)
kvm_x86_ops.cpu_dirty_log_size;
}

-int mmu_try_to_unsync_pages(struct kvm_vcpu *vcpu, gfn_t gfn, bool can_unsync);
+int mmu_try_to_unsync_pages(struct kvm_vcpu *vcpu, gfn_t gfn, bool can_unsync,
+ bool speculative);

void kvm_mmu_gfn_disallow_lpage(const struct kvm_memory_slot *slot, gfn_t gfn);
void kvm_mmu_gfn_allow_lpage(const struct kvm_memory_slot *slot, gfn_t gfn);
diff --git a/arch/x86/kvm/mmu/spte.c b/arch/x86/kvm/mmu/spte.c
index 3e97cdb13eb7..b68a580f3510 100644
--- a/arch/x86/kvm/mmu/spte.c
+++ b/arch/x86/kvm/mmu/spte.c
@@ -159,7 +159,7 @@ int make_spte(struct kvm_vcpu *vcpu, unsigned int pte_access, int level,
* e.g. it's write-tracked (upper-level SPs) or has one or more
* shadow pages and unsync'ing pages is not allowed.
*/
- if (mmu_try_to_unsync_pages(vcpu, gfn, can_unsync)) {
+ if (mmu_try_to_unsync_pages(vcpu, gfn, can_unsync, speculative)) {
pgprintk("%s: found shadow page for %llx, marking ro\n",
__func__, gfn);
ret |= SET_SPTE_WRITE_PROTECTED_PT;
--
2.19.1.6.gb485710b