KVM: X86: Synchronize the shadow pagetable before link it
If gpte is changed from non-present to present, the guest doesn't need
to flush tlb per SDM. So the host must synchronze sp before
link it. Otherwise the guest might use a wrong mapping.
For example: the guest first changes a level-1 pagetable, and then
links its parent to a new place where the original gpte is non-present.
Finally the guest can access the remapped area without flushing
the tlb. The guest's behavior should be allowed per SDM, but the host
kvm mmu makes it wrong.
Fixes: 4731d4c7a077 ("KVM: MMU: out of sync shadow core")
Signed-off-by: Lai Jiangshan <laijs@linux.alibaba.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Message-Id: <20210918005636.3675-3-jiangshanlai@gmail.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index 2d7e611..1a64ba5 100644
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -2027,8 +2027,8 @@
} while (!sp->unsync_children);
}
-static void mmu_sync_children(struct kvm_vcpu *vcpu,
- struct kvm_mmu_page *parent)
+static int mmu_sync_children(struct kvm_vcpu *vcpu,
+ struct kvm_mmu_page *parent, bool can_yield)
{
int i;
struct kvm_mmu_page *sp;
@@ -2055,12 +2055,18 @@
}
if (need_resched() || rwlock_needbreak(&vcpu->kvm->mmu_lock)) {
kvm_mmu_flush_or_zap(vcpu, &invalid_list, false, flush);
+ if (!can_yield) {
+ kvm_make_request(KVM_REQ_MMU_SYNC, vcpu);
+ return -EINTR;
+ }
+
cond_resched_rwlock_write(&vcpu->kvm->mmu_lock);
flush = false;
}
}
kvm_mmu_flush_or_zap(vcpu, &invalid_list, false, flush);
+ return 0;
}
static void __clear_sp_write_flooding_count(struct kvm_mmu_page *sp)
@@ -2146,9 +2152,6 @@
kvm_make_request(KVM_REQ_TLB_FLUSH_CURRENT, vcpu);
}
- if (sp->unsync_children)
- kvm_make_request(KVM_REQ_MMU_SYNC, vcpu);
-
__clear_sp_write_flooding_count(sp);
trace_get_page:
@@ -3684,7 +3687,7 @@
write_lock(&vcpu->kvm->mmu_lock);
kvm_mmu_audit(vcpu, AUDIT_PRE_SYNC);
- mmu_sync_children(vcpu, sp);
+ mmu_sync_children(vcpu, sp, true);
kvm_mmu_audit(vcpu, AUDIT_POST_SYNC);
write_unlock(&vcpu->kvm->mmu_lock);
@@ -3700,7 +3703,7 @@
if (IS_VALID_PAE_ROOT(root)) {
root &= PT64_BASE_ADDR_MASK;
sp = to_shadow_page(root);
- mmu_sync_children(vcpu, sp);
+ mmu_sync_children(vcpu, sp, true);
}
}
diff --git a/arch/x86/kvm/mmu/paging_tmpl.h b/arch/x86/kvm/mmu/paging_tmpl.h
index efce0a9..913d52a7 100644
--- a/arch/x86/kvm/mmu/paging_tmpl.h
+++ b/arch/x86/kvm/mmu/paging_tmpl.h
@@ -707,8 +707,27 @@
if (!is_shadow_present_pte(*it.sptep)) {
table_gfn = gw->table_gfn[it.level - 2];
access = gw->pt_access[it.level - 2];
- sp = kvm_mmu_get_page(vcpu, table_gfn, addr, it.level-1,
- false, access);
+ sp = kvm_mmu_get_page(vcpu, table_gfn, addr,
+ it.level-1, false, access);
+ /*
+ * We must synchronize the pagetable before linking it
+ * because the guest doesn't need to flush tlb when
+ * the gpte is changed from non-present to present.
+ * Otherwise, the guest may use the wrong mapping.
+ *
+ * For PG_LEVEL_4K, kvm_mmu_get_page() has already
+ * synchronized it transiently via kvm_sync_page().
+ *
+ * For higher level pagetable, we synchronize it via
+ * the slower mmu_sync_children(). If it needs to
+ * break, some progress has been made; return
+ * RET_PF_RETRY and retry on the next #PF.
+ * KVM_REQ_MMU_SYNC is not necessary but it
+ * expedites the process.
+ */
+ if (sp->unsync_children &&
+ mmu_sync_children(vcpu, sp, false))
+ return RET_PF_RETRY;
}
/*
