Skip to content

Commit

Permalink
KVM: MMU: Introduce drop_spte()
Browse files Browse the repository at this point in the history 
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 <[email protected]>
  • Loading branch information
@avikivity
avikivity committed Aug 2, 2010
1 parent dd180b3 commit be38d27
Show file tree
Hide file tree
Showing 2 changed files with 23 additions and 20 deletions.
30 changes: 17 additions & 13 deletions arch/x86/kvm/mmu.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -658,6 +658,12 @@ 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;
Expand Down Expand Up @@ -722,9 +728,9 @@ 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;
}
Expand All @@ -744,8 +750,7 @@ 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;
Expand All @@ -767,8 +772,7 @@ 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);
Expand Down Expand Up @@ -1464,7 +1468,8 @@ 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;
Expand Down Expand Up @@ -1868,9 +1873,8 @@ 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;
Expand Down Expand Up @@ -1902,6 +1906,7 @@ static int set_spte(struct kvm_vcpu *vcpu, u64 *sptep,

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

Expand Down Expand Up @@ -1938,8 +1943,7 @@ 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);
__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;
Expand Down Expand Up @@ -2591,7 +2595,7 @@ 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);
Expand Down
13 changes: 6 additions & 7 deletions arch/x86/kvm/paging_tmpl.h
View file
Original file line number Diff line number Diff line change
Expand Up @@ -353,8 +353,7 @@ static u64 *FNAME(fetch)(struct kvm_vcpu *vcpu, gva_t addr,
}

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);
}

Expand Down Expand Up @@ -516,12 +515,13 @@ 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;
}

Expand Down Expand Up @@ -637,12 +637,11 @@ 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) || !clear_unsync)
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;
}

Expand Down

0 comments on commit be38d27

Please sign in to comment.