[PATCH 39/58] KVM: Make shadow pte updates atomic

Avi Kivity
2007-06-17T09:44:20Z

With guest smp, a second vcpu might see partial updates when the first
vcpu services a page fault. So delay all updates until we have figured
out what the pte should look like.

Note that on i386, this is still not completely atomic as a 64-bit write
will be split into two on a 32-bit machine.

Signed-off-by: Avi Kivity <avi-atKUWr5tajBWk0Htik3J/w@public.gmane.org>
---
drivers/kvm/paging_tmpl.h | 37 ++++++++++++++++++++-----------------
1 files changed, 20 insertions(+), 17 deletions(-)

diff --git a/drivers/kvm/paging_tmpl.h b/drivers/kvm/paging_tmpl.h
index 35f264f..397a403 100644
--- a/drivers/kvm/paging_tmpl.h
+++ b/drivers/kvm/paging_tmpl.h
@@ -205,11 +205,12 @@ static void FNAME(set_pte_common)(struct kvm_vcpu *vcpu,
{
hpa_t paddr;
int dirty = *gpte & PT_DIRTY_MASK;
- int was_rmapped = is_rmap_pte(*shadow_pte);
+ u64 spte = *shadow_pte;
+ int was_rmapped = is_rmap_pte(spte);

pgprintk("%s: spte %llx gpte %llx access %llx write_fault %d"
" user_fault %d gfn %lx\n",
- __FUNCTION__, *shadow_pte, (u64)*gpte, access_bits,
+ __FUNCTION__, spte, (u64)*gpte, access_bits,
write_fault, user_fault, gfn);

if (write_fault && !dirty) {
@@ -218,34 +219,35 @@ static void FNAME(set_pte_common)(struct kvm_vcpu *vcpu,
FNAME(mark_pagetable_dirty)(vcpu->kvm, walker);
}

- *shadow_pte |= *gpte & PT_PTE_COPY_MASK;
- *shadow_pte |= access_bits << PT_SHADOW_BITS_OFFSET;
+ spte |= *gpte & PT_PTE_COPY_MASK;
+ spte |= access_bits << PT_SHADOW_BITS_OFFSET;
if (!dirty)
access_bits &= ~PT_WRITABLE_MASK;

paddr = gpa_to_hpa(vcpu, gaddr & PT64_BASE_ADDR_MASK);

- *shadow_pte |= PT_PRESENT_MASK;
+ spte |= PT_PRESENT_MASK;
if (access_bits & PT_USER_MASK)
- *shadow_pte |= PT_USER_MASK;
+ spte |= PT_USER_MASK;

if (is_error_hpa(paddr)) {
- *shadow_pte |= gaddr;
- *shadow_pte |= PT_SHADOW_IO_MARK;
- *shadow_pte &= ~PT_PRESENT_MASK;
+ spte |= gaddr;
+ spte |= PT_SHADOW_IO_MARK;
+ spte &= ~PT_PRESENT_MASK;
+ *shadow_pte = spte;
return;
}

- *shadow_pte |= paddr;
+ spte |= paddr;

- if (!write_fault && (*shadow_pte & PT_SHADOW_USER_MASK) &&
- !(*shadow_pte & PT_USER_MASK)) {
+ if (!write_fault && (spte & PT_SHADOW_USER_MASK) &&
+ !(spte & PT_USER_MASK)) {
/*
* If supervisor write protect is disabled, we shadow kernel
* pages as user pages so we can trap the write access.
*/
- *shadow_pte |= PT_USER_MASK;
- *shadow_pte &= ~PT_WRITABLE_MASK;
+ spte |= PT_USER_MASK;
+ spte &= ~PT_WRITABLE_MASK;
access_bits &= ~PT_WRITABLE_MASK;
}

@@ -253,7 +255,7 @@ static void FNAME(set_pte_common)(struct kvm_vcpu *vcpu,
|| (write_fault && !is_write_protection(vcpu) && !user_fault)) {
struct kvm_mmu_page *shadow;

- *shadow_pte |= PT_WRITABLE_MASK;
+ spte |= PT_WRITABLE_MASK;
if (user_fault) {
mmu_unshadow(vcpu, gfn);
goto unshadowed;
@@ -264,8 +266,8 @@ static void FNAME(set_pte_common)(struct kvm_vcpu *vcpu,
pgprintk("%s: found shadow page for %lx, marking ro\n",
__FUNCTION__, gfn);
access_bits &= ~PT_WRITABLE_MASK;
- if (is_writeble_pte(*shadow_pte)) {
- *shadow_pte &= ~PT_WRITABLE_MASK;
+ if (is_writeble_pte(spte)) {
+ spte &= ~PT_WRITABLE_MASK;
kvm_arch_ops->tlb_flush(vcpu);
}
if (write_fault)
@@ -278,6 +280,7 @@ unshadowed:
if (access_bits & PT_WRITABLE_MASK)
mark_page_dirty(vcpu->kvm, gaddr >> PAGE_SHIFT);

+ *shadow_pte = spte;
page_header_update_slot(vcpu->kvm, shadow_pte, gaddr);
if (!was_rmapped)
rmap_add(vcpu, shadow_pte);