KVM: MMU: Introduce drop_spte()
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>
diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
index 70cdf68..1ad39cf 100644
--- a/arch/x86/kvm/mmu.c
+++ b/arch/x86/kvm/mmu.c
@@ -658,6 +658,12 @@
}
}
+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;
@@ -722,9 +728,9 @@
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;
}
@@ -744,8 +750,7 @@
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;
@@ -767,8 +772,7 @@
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);
@@ -1464,7 +1468,8 @@
} 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;
@@ -1868,9 +1873,8 @@
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;
@@ -1902,6 +1906,7 @@
set_pte:
__set_spte(sptep, spte);
+done:
return ret;
}
@@ -1938,8 +1943,7 @@
} else if (pfn != spte_to_pfn(*sptep)) {
pgprintk("hfn old %lx new %lx\n",
spte_to_pfn(*sptep), pfn);
- 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);
} else
was_rmapped = 1;
@@ -2591,7 +2595,7 @@
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);