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@xxxxxxxxxxxxxx>
---
arch/x86/kvm/mmu.c | 107 +++++++++++++++++++++++++++++++++++++++++++-
arch/x86/kvm/paging_tmpl.h | 81 ++++++++++++++++++++++++++++++++-
2 files changed, 184 insertions(+), 4 deletions(-)
diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
index 9c69725..4501734 100644
--- a/arch/x86/kvm/mmu.c
+++ b/arch/x86/kvm/mmu.c
@@ -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
@@ -403,7 +405,7 @@ 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);
@@ -2090,6 +2092,108 @@ 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];
+ struct kvm_memory_slot *slot;
+ unsigned hva, access = sp->role.access;
+ int i, ret, npages = end - start;
+ gfn_t gfn;
+
+ gfn = kvm_mmu_page_get_gfn(sp, start - sp->spt);
+ slot = pte_prefetch_gfn_to_memslot(vcpu, gfn, access & ACC_WRITE_MASK);
+ if (!slot || slot->npages - (gfn - slot->base_gfn) != npages)
+ return -1;
+
+ hva = gfn_to_hva_memslot(slot, gfn);
+ ret = __get_user_pages_fast(hva, npages, 1, pages);
+ 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 ret == npages ? 0 : -1;
+}
+
+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)
{
@@ -2103,6 +2207,7 @@ 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;
}
diff --git a/arch/x86/kvm/paging_tmpl.h b/arch/x86/kvm/paging_tmpl.h
index 51ef909..114c17d 100644
--- a/arch/x86/kvm/paging_tmpl.h
+++ b/arch/x86/kvm/paging_tmpl.h
@@ -67,6 +67,7 @@ struct guest_walker {
int level;
gfn_t table_gfn[PT_MAX_FULL_LEVELS];
pt_element_t ptes[PT_MAX_FULL_LEVELS];
+ pt_element_t prefetch_ptes[PTE_PREFETCH_NUM];
gpa_t pte_gpa[PT_MAX_FULL_LEVELS];
unsigned pt_access;
unsigned pte_access;
@@ -302,14 +303,87 @@ static void FNAME(update_pte)(struct kvm_vcpu *vcpu, struct kvm_mmu_page *sp,
static bool FNAME(gpte_changed)(struct kvm_vcpu *vcpu,
struct guest_walker *gw, int level)
{
- int r;
pt_element_t curr_pte;
-
- r = kvm_read_guest_atomic(vcpu->kvm, gw->pte_gpa[level - 1],
+ gpa_t base_gpa, pte_gpa = gw->pte_gpa[level - 1];
+ u64 mask;
+ int r, index;
+
+ if (level == PT_PAGE_TABLE_LEVEL) {
+ mask = PTE_PREFETCH_NUM * sizeof(pt_element_t) - 1;
+ base_gpa = pte_gpa & ~mask;
+ index = (pte_gpa - base_gpa) / sizeof(pt_element_t);
+
+ r = kvm_read_guest_atomic(vcpu->kvm, base_gpa,
+ gw->prefetch_ptes, sizeof(gw->prefetch_ptes));
+ curr_pte = gw->prefetch_ptes[index];
+ } else
+ r = kvm_read_guest_atomic(vcpu->kvm, pte_gpa,
&curr_pte, sizeof(curr_pte));
+
return r || curr_pte != gw->ptes[level - 1];
}
+static void FNAME(pte_prefetch)(struct kvm_vcpu *vcpu, struct guest_walker *gw,
+ u64 *sptep)
+{
+ struct kvm_mmu_page *sp;
+ pt_element_t *gptep = gw->prefetch_ptes;
+ u64 *spte;
+ int i;
+
+ sp = page_header(__pa(sptep));
+
+ if (sp->role.level > PT_PAGE_TABLE_LEVEL)
+ return;
+
+ if (sp->role.direct)
+ return __direct_pte_prefetch(vcpu, sp, sptep);
+
+ i = (sptep - sp->spt) & ~(PTE_PREFETCH_NUM - 1);
+ spte = sp->spt + i;
+
+ for (i = 0; i < PTE_PREFETCH_NUM; i++, spte++) {
+ pt_element_t gpte;
+ unsigned pte_access;
+ gfn_t gfn;
+ pfn_t pfn;
+ bool dirty;
+
+ if (spte == sptep)
+ continue;
+
+ if (*spte != shadow_trap_nonpresent_pte)
+ continue;
+
+ gpte = gptep[i];
+
+
+ if (!is_present_gpte(gpte) ||
+ is_rsvd_bits_set(vcpu, gpte, PT_PAGE_TABLE_LEVEL)) {
+ if (!sp->unsync)
+ __set_spte(spte, shadow_notrap_nonpresent_pte);
+ continue;
+ }
+
+ if (!(gpte & PT_ACCESSED_MASK))
+ continue;
+
+ pte_access = sp->role.access & FNAME(gpte_access)(vcpu, gpte);
+ gfn = gpte_to_gfn(gpte);
+ dirty = is_dirty_gpte(gpte);
+ pfn = pte_prefetch_gfn_to_pfn(vcpu, gfn,
+ (pte_access & ACC_WRITE_MASK) && dirty);
+ if (is_error_pfn(pfn)) {
+ kvm_release_pfn_clean(pfn);
+ break;
+ }
+
+ mmu_set_spte(vcpu, spte, sp->role.access, pte_access, 0, 0,
+ dirty, NULL, PT_PAGE_TABLE_LEVEL, gfn,
+ pfn, true, true);
+ }
+}
+
/*
* Fetch a shadow pte for a specific level in the paging hierarchy.
*/
@@ -391,6 +465,7 @@ static u64 *FNAME(fetch)(struct kvm_vcpu *vcpu, gva_t addr,
mmu_set_spte(vcpu, it.sptep, access, gw->pte_access & access,
user_fault, write_fault, dirty, ptwrite, it.level,
gw->gfn, pfn, false, true);
+ FNAME(pte_prefetch)(vcpu, gw, it.sptep);
return it.sptep;
--
1.6.1.2
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