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KVM: MMU: prefetch ptes when intercepted guest #PF

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Support prefetch ptes when intercept guest #PF, avoid to #PF by later
access

If we meet any failure in the prefetch path, we will exit it and
not try other ptes to avoid become heavy path

Signed-off-by: Xiao Guangrong <xiaoguangrong@cn.fujitsu.com>
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
This commit is contained in:
Xiao Guangrong
2010-08-22 19:12:48 +08:00
committed by Avi Kivity
parent 48987781eb
commit 957ed9effd
2 changed files with 175 additions and 1 deletions
Download Patch File Download Diff File Expand all files Collapse all files

104
arch/x86/kvm/mmu.c
View File

@@ -89,6 +89,8 @@ module_param(oos_shadow, bool, 0644);
}
#endif
#define PTE_PREFETCH_NUM 8
#define PT_FIRST_AVAIL_BITS_SHIFT 9
#define PT64_SECOND_AVAIL_BITS_SHIFT 52
@@ -400,7 +402,7 @@ static int mmu_topup_memory_caches(struct kvm_vcpu *vcpu)
if (r)
goto out;
r = mmu_topup_memory_cache(&vcpu->arch.mmu_rmap_desc_cache,
rmap_desc_cache, 4);
rmap_desc_cache, 4 + PTE_PREFETCH_NUM);
if (r)
goto out;
r = mmu_topup_memory_cache_page(&vcpu->arch.mmu_page_cache, 8);
@@ -2089,6 +2091,105 @@ static void nonpaging_new_cr3(struct kvm_vcpu *vcpu)
{
}
static struct kvm_memory_slot *
pte_prefetch_gfn_to_memslot(struct kvm_vcpu *vcpu, gfn_t gfn, bool no_dirty_log)
{
struct kvm_memory_slot *slot;
slot = gfn_to_memslot(vcpu->kvm, gfn);
if (!slot || slot->flags & KVM_MEMSLOT_INVALID ||
(no_dirty_log && slot->dirty_bitmap))
slot = NULL;
return slot;
}
static pfn_t pte_prefetch_gfn_to_pfn(struct kvm_vcpu *vcpu, gfn_t gfn,
bool no_dirty_log)
{
struct kvm_memory_slot *slot;
unsigned long hva;
slot = pte_prefetch_gfn_to_memslot(vcpu, gfn, no_dirty_log);
if (!slot) {
get_page(bad_page);
return page_to_pfn(bad_page);
}
hva = gfn_to_hva_memslot(slot, gfn);
return hva_to_pfn_atomic(vcpu->kvm, hva);
}
static int direct_pte_prefetch_many(struct kvm_vcpu *vcpu,
struct kvm_mmu_page *sp,
u64 *start, u64 *end)
{
struct page *pages[PTE_PREFETCH_NUM];
unsigned access = sp->role.access;
int i, ret;
gfn_t gfn;
gfn = kvm_mmu_page_get_gfn(sp, start - sp->spt);
if (!pte_prefetch_gfn_to_memslot(vcpu, gfn, access & ACC_WRITE_MASK))
return -1;
ret = gfn_to_page_many_atomic(vcpu->kvm, gfn, pages, end - start);
if (ret <= 0)
return -1;
for (i = 0; i < ret; i++, gfn++, start++)
mmu_set_spte(vcpu, start, ACC_ALL,
access, 0, 0, 1, NULL,
sp->role.level, gfn,
page_to_pfn(pages[i]), true, true);
return 0;
}
static void __direct_pte_prefetch(struct kvm_vcpu *vcpu,
struct kvm_mmu_page *sp, u64 *sptep)
{
u64 *spte, *start = NULL;
int i;
WARN_ON(!sp->role.direct);
i = (sptep - sp->spt) & ~(PTE_PREFETCH_NUM - 1);
spte = sp->spt + i;
for (i = 0; i < PTE_PREFETCH_NUM; i++, spte++) {
if (*spte != shadow_trap_nonpresent_pte || spte == sptep) {
if (!start)
continue;
if (direct_pte_prefetch_many(vcpu, sp, start, spte) < 0)
break;
start = NULL;
} else if (!start)
start = spte;
}
}
static void direct_pte_prefetch(struct kvm_vcpu *vcpu, u64 *sptep)
{
struct kvm_mmu_page *sp;
/*
* Since it's no accessed bit on EPT, it's no way to
* distinguish between actually accessed translations
* and prefetched, so disable pte prefetch if EPT is
* enabled.
*/
if (!shadow_accessed_mask)
return;
sp = page_header(__pa(sptep));
if (sp->role.level > PT_PAGE_TABLE_LEVEL)
return;
__direct_pte_prefetch(vcpu, sp, sptep);
}
static int __direct_map(struct kvm_vcpu *vcpu, gpa_t v, int write,
int level, gfn_t gfn, pfn_t pfn)
{
@@ -2102,6 +2203,7 @@ static int __direct_map(struct kvm_vcpu *vcpu, gpa_t v, int write,
mmu_set_spte(vcpu, iterator.sptep, ACC_ALL, ACC_ALL,
0, write, 1, &pt_write,
level, gfn, pfn, false, true);
direct_pte_prefetch(vcpu, iterator.sptep);
++vcpu->stat.pf_fixed;
break;
}