[PATCH v2 1/4] KVM: MMU: Introduce drop_spte()

Avi Kivity
2010-06-07T07:11:01Z

When we call rmap_remove(), we (almost) always immediately follow it by
an __set_spte() to a nonpresent pte. Since we need to perform the two
operations atomically, to avoid losing the dirty and accessed bits, introduce
a helper drop_spte() and convert all call sites.

The operation is still nonatomic at this point.

Signed-off-by: Avi Kivity <avi@redhat.com>
---
arch/x86/kvm/mmu.c | 29 +++++++++++++++++------------
arch/x86/kvm/paging_tmpl.h | 13 ++++++-------
2 files changed, 23 insertions(+), 19 deletions(-)

diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
index 6b2c644..16cedc9 100644
--- a/arch/x86/kvm/mmu.c
+++ b/arch/x86/kvm/mmu.c
@@ -666,6 +666,12 @@ static void rmap_remove(struct kvm *kvm, u64 *spte)
}
}

+static void drop_spte(struct kvm *kvm, u64 *sptep, u64 new_spte)
+{
+ rmap_remove(kvm, sptep);
+ __set_spte(sptep, new_spte);
+}
+
static u64 *rmap_next(struct kvm *kvm, unsigned long *rmapp, u64 *spte)
{
struct kvm_rmap_desc *desc;
@@ -731,9 +737,9 @@ static int rmap_write_protect(struct kvm *kvm, u64 gfn)
BUG_ON((*spte & (PT_PAGE_SIZE_MASK|PT_PRESENT_MASK)) != (PT_PAGE_SIZE_MASK|PT_PRESENT_MASK));
pgprintk("rmap_write_protect(large): spte %p %llx %lld\n", spte, *spte, gfn);
if (is_writable_pte(*spte)) {
- rmap_remove(kvm, spte);
+ drop_spte(kvm, spte,
+ shadow_trap_nonpresent_pte);
--kvm->stat.lpages;
- __set_spte(spte, shadow_trap_nonpresent_pte);
spte = NULL;
write_protected = 1;
}
@@ -753,8 +759,7 @@ static int kvm_unmap_rmapp(struct kvm *kvm, unsigned long *rmapp,
while ((spte = rmap_next(kvm, rmapp, NULL))) {
BUG_ON(!(*spte & PT_PRESENT_MASK));
rmap_printk("kvm_rmap_unmap_hva: spte %p %llx\n", spte, *spte);
- rmap_remove(kvm, spte);
- __set_spte(spte, shadow_trap_nonpresent_pte);
+ drop_spte(kvm, spte, shadow_trap_nonpresent_pte);
need_tlb_flush = 1;
}
return need_tlb_flush;
@@ -776,8 +781,7 @@ static int kvm_set_pte_rmapp(struct kvm *kvm, unsigned long *rmapp,
rmap_printk("kvm_set_pte_rmapp: spte %p %llx\n", spte, *spte);
need_flush = 1;
if (pte_write(*ptep)) {
- rmap_remove(kvm, spte);
- __set_spte(spte, shadow_trap_nonpresent_pte);
+ drop_spte(kvm, spte, shadow_trap_nonpresent_pte);
spte = rmap_next(kvm, rmapp, NULL);
} else {
new_spte = *spte &~ (PT64_BASE_ADDR_MASK);
@@ -1501,7 +1505,8 @@ static void kvm_mmu_page_unlink_children(struct kvm *kvm,
} else {
if (is_large_pte(ent))
--kvm->stat.lpages;
- rmap_remove(kvm, &pt[i]);
+ drop_spte(kvm, &pt[i],
+ shadow_trap_nonpresent_pte);
}
}
pt[i] = shadow_trap_nonpresent_pte;
@@ -1902,9 +1907,8 @@ static int set_spte(struct kvm_vcpu *vcpu, u64 *sptep,
if (level > PT_PAGE_TABLE_LEVEL &&
has_wrprotected_page(vcpu->kvm, gfn, level)) {
ret = 1;
- rmap_remove(vcpu->kvm, sptep);
- spte = shadow_trap_nonpresent_pte;
- goto set_pte;
+ drop_spte(vcpu->kvm, sptep, shadow_trap_nonpresent_pte);
+ goto done;
}

spte |= PT_WRITABLE_MASK;
@@ -1936,6 +1940,7 @@ static int set_spte(struct kvm_vcpu *vcpu, u64 *sptep,

set_pte:
__set_spte(sptep, spte);
+done:
return ret;
}

@@ -1972,7 +1977,7 @@ static void mmu_set_spte(struct kvm_vcpu *vcpu, u64 *sptep,
} else if (pfn != spte_to_pfn(*sptep)) {
pgprintk("hfn old %lx new %lx\n",
spte_to_pfn(*sptep), pfn);
- rmap_remove(vcpu->kvm, sptep);
+ drop_spte(vcpu->kvm, sptep, shadow_trap_nonpresent_pte);
} else
was_rmapped = 1;
}
@@ -2623,7 +2628,7 @@ static void mmu_pte_write_zap_pte(struct kvm_vcpu *vcpu,
pte = *spte;
if (is_shadow_present_pte(pte)) {
if (is_last_spte(pte, sp->role.level))
- rmap_remove(vcpu->kvm, spte);
+ drop_spte(vcpu->kvm, spte, shadow_trap_nonpresent_pte);
else {
child = page_header(pte & PT64_BASE_ADDR_MASK);
mmu_page_remove_parent_pte(child, spte);
diff --git a/arch/x86/kvm/paging_tmpl.h b/arch/x86/kvm/paging_tmpl.h
index 8f1ef87..105176d 100644
--- a/arch/x86/kvm/paging_tmpl.h
+++ b/arch/x86/kvm/paging_tmpl.h
@@ -329,8 +329,7 @@ static u64 *FNAME(fetch)(struct kvm_vcpu *vcpu, gva_t addr,
continue;

if (is_large_pte(*sptep)) {
- rmap_remove(vcpu->kvm, sptep);
- __set_spte(sptep, shadow_trap_nonpresent_pte);
+ drop_spte(vcpu->kvm, sptep, shadow_trap_nonpresent_pte);
kvm_flush_remote_tlbs(vcpu->kvm);
}

@@ -491,12 +490,13 @@ static void FNAME(invlpg)(struct kvm_vcpu *vcpu, gva_t gva)
pte_gpa += (sptep - sp->spt) * sizeof(pt_element_t);

if (is_shadow_present_pte(*sptep)) {
- rmap_remove(vcpu->kvm, sptep);
if (is_large_pte(*sptep))
--vcpu->kvm->stat.lpages;
+ drop_spte(vcpu->kvm, sptep,
+ shadow_trap_nonpresent_pte);
need_flush = 1;
- }
- __set_spte(sptep, shadow_trap_nonpresent_pte);
+ } else
+ __set_spte(sptep, shadow_trap_nonpresent_pte);
break;
}

@@ -612,12 +612,11 @@ static int FNAME(sync_page)(struct kvm_vcpu *vcpu, struct kvm_mmu_page *sp)
!is_present_gpte(gpte) || !(gpte & PT_ACCESSED_MASK)) {
u64 nonpresent;

- rmap_remove(vcpu->kvm, &sp->spt[i]);
if (is_present_gpte(gpte))
nonpresent = shadow_trap_nonpresent_pte;
else
nonpresent = shadow_notrap_nonpresent_pte;
- __set_spte(&sp->spt[i], nonpresent);
+ drop_spte(vcpu->kvm, &sp->spt[i], nonpresent);
continue;
}

--
1.7.1