[PATCH 1/2] KVM: MMU: don't make direct sp read-only if !map_writable

Xiao Guangrong
2010-12-13T10:26:50Z

Currently, if the page is not allowed to write, then it can drop
ACC_WRITE_MASK in pte_access, and the direct sp's access is:
gw->pt_access & gw->pte_access
so, it also removes the write access in the direct sp.

There is a problem: if the access of those pages which map thought the same
mapping in guest is different in host, it causes host switch direct sp very
frequently.

Signed-off-by: Xiao Guangrong <xiaoguangrong@cn.fujitsu.com>
---
arch/x86/kvm/mmu.c | 4 ++--
arch/x86/kvm/paging_tmpl.h | 11 ++---------
2 files changed, 4 insertions(+), 11 deletions(-)

diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
index 1a953ac..0c5cad0 100644
--- a/arch/x86/kvm/mmu.c
+++ b/arch/x86/kvm/mmu.c
@@ -1987,6 +1987,8 @@ static int set_spte(struct kvm_vcpu *vcpu, u64 *sptep,

if (host_writable)
spte |= SPTE_HOST_WRITEABLE;
+ else
+ pte_access &= ~ACC_WRITE_MASK;

spte |= (u64)pfn << PAGE_SHIFT;

@@ -2226,8 +2228,6 @@ static int __direct_map(struct kvm_vcpu *vcpu, gpa_t v, int write,
if (iterator.level == level) {
unsigned pte_access = ACC_ALL;

- if (!map_writable)
- pte_access &= ~ACC_WRITE_MASK;
mmu_set_spte(vcpu, iterator.sptep, ACC_ALL, pte_access,
0, write, 1, &pt_write,
level, gfn, pfn, prefault, map_writable);
diff --git a/arch/x86/kvm/paging_tmpl.h b/arch/x86/kvm/paging_tmpl.h
index 146b681..6ed2c5e 100644
--- a/arch/x86/kvm/paging_tmpl.h
+++ b/arch/x86/kvm/paging_tmpl.h
@@ -593,9 +593,6 @@ static int FNAME(page_fault)(struct kvm_vcpu *vcpu, gva_t addr, u32 error_code,
if (is_error_pfn(pfn))
return kvm_handle_bad_page(vcpu->kvm, walker.gfn, pfn);

- if (!map_writable)
- walker.pte_access &= ~ACC_WRITE_MASK;
-
spin_lock(&vcpu->kvm->mmu_lock);
if (mmu_notifier_retry(vcpu, mmu_seq))
goto out_unlock;
@@ -809,12 +806,8 @@ static int FNAME(sync_page)(struct kvm_vcpu *vcpu, struct kvm_mmu_page *sp)

nr_present++;
pte_access = sp->role.access & FNAME(gpte_access)(vcpu, gpte);
- if (!(sp->spt[i] & SPTE_HOST_WRITEABLE)) {
- pte_access &= ~ACC_WRITE_MASK;
- host_writable = 0;
- } else {
- host_writable = 1;
- }
+ host_writable = !!(sp->spt[i] & SPTE_HOST_WRITEABLE);
+
set_spte(vcpu, &sp->spt[i], pte_access, 0, 0,
is_dirty_gpte(gpte), PT_PAGE_TABLE_LEVEL, gfn,
spte_to_pfn(sp->spt[i]), true, false,
--
1.7.0.4