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Subject[PATCH v5 7/9] KVM: MMU: prefetch ptes when intercepted guest #PF
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

Will do: fix dirty bit tracking in the speculative path

Signed-off-by: Xiao Guangrong <xiaoguangrong@cn.fujitsu.com>
---
arch/x86/kvm/mmu.c | 79 ++++++++++++++++++++++++++++++++++++++++++++
arch/x86/kvm/paging_tmpl.h | 76 ++++++++++++++++++++++++++++++++++++++++++
2 files changed, 155 insertions(+), 0 deletions(-)
diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
index cda4587..66e225d 100644
--- a/arch/x86/kvm/mmu.c
+++ b/arch/x86/kvm/mmu.c
@@ -2038,6 +2038,84 @@ static void nonpaging_new_cr3(struct kvm_vcpu *vcpu)
{
}

+static int direct_pte_prefetch_many(struct kvm_vcpu *vcpu,
+ struct kvm_mmu_page *sp,
+ u64 *start, u64 *end)
+{
+ gfn_t gfn;
+ struct page *pages[PTE_PREFETCH_NUM];
+
+ gfn = sp->gfn + start - sp->spt;
+ while (start < end) {
+ int j, ret;
+ bool enough;
+
+ ret = gfn_to_page_many_atomic(vcpu->kvm, gfn, pages,
+ end - start, &enough);
+ if (ret <= 0)
+ return -1;
+
+ for (j = 0; j < ret; j++, gfn++, start++)
+ mmu_set_spte(vcpu, start, ACC_ALL,
+ sp->role.access, 0, 0, 1, NULL,
+ sp->role.level, gfn,
+ page_to_pfn(pages[j]), true, true);
+
+ if (!enough)
+ return -1;
+ }
+ return 0;
+}
+
+static void __direct_pte_prefetch(struct kvm_vcpu *vcpu,
+ struct kvm_mmu_page *sp, u64 *sptep)
+{
+ u64 *start = NULL;
+ int index, i, max;
+
+ WARN_ON(!sp->role.direct);
+
+ if (pte_prefetch_topup_memory_cache(vcpu))
+ return;
+
+ index = sptep - sp->spt;
+ i = index & ~(PTE_PREFETCH_NUM - 1);
+ max = index | (PTE_PREFETCH_NUM - 1);
+
+ for (; i < max; i++) {
+ u64 *spte = sp->spt + i;
+
+ 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)
{
@@ -2051,6 +2129,7 @@ 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 f58a5c4..e04c1a4 100644
--- a/arch/x86/kvm/paging_tmpl.h
+++ b/arch/x86/kvm/paging_tmpl.h
@@ -291,6 +291,81 @@ static void FNAME(update_pte)(struct kvm_vcpu *vcpu, struct kvm_mmu_page *sp,
gpte_to_gfn(gpte), pfn, true, true);
}

+static void FNAME(pte_prefetch)(struct kvm_vcpu *vcpu, u64 *sptep)
+{
+ struct kvm_mmu_page *sp;
+ pt_element_t gptep[PTE_PREFETCH_NUM];
+ gpa_t first_pte_gpa;
+ int offset = 0, index, i, j, max;
+
+ sp = page_header(__pa(sptep));
+ index = sptep - sp->spt;
+
+ if (sp->role.level > PT_PAGE_TABLE_LEVEL)
+ return;
+
+ if (sp->role.direct)
+ return __direct_pte_prefetch(vcpu, sp, sptep);
+
+ index = sptep - sp->spt;
+ i = index & ~(PTE_PREFETCH_NUM - 1);
+ max = index | (PTE_PREFETCH_NUM - 1);
+
+ if (PTTYPE == 32)
+ offset = sp->role.quadrant << PT64_LEVEL_BITS;
+
+ first_pte_gpa = gfn_to_gpa(sp->gfn) +
+ (offset + i) * sizeof(pt_element_t);
+
+ if (kvm_read_guest_atomic(vcpu->kvm, first_pte_gpa, gptep,
+ sizeof(gptep)) < 0)
+ return;
+
+ if (pte_prefetch_topup_memory_cache(vcpu))
+ return;
+
+ for (j = 0; i < max; i++, j++) {
+ pt_element_t gpte;
+ unsigned pte_access;
+ u64 *spte = sp->spt + i;
+ gfn_t gfn;
+ pfn_t pfn;
+
+ if (spte == sptep)
+ continue;
+
+ if (*spte != shadow_trap_nonpresent_pte)
+ continue;
+
+ gpte = gptep[j];
+
+ if (is_rsvd_bits_set(vcpu, gpte, PT_PAGE_TABLE_LEVEL))
+ break;
+
+ if (!(gpte & PT_ACCESSED_MASK))
+ continue;
+
+ if (!is_present_gpte(gpte)) {
+ if (!sp->unsync)
+ __set_spte(spte, shadow_notrap_nonpresent_pte);
+ continue;
+ }
+
+ gfn = gpte_to_gfn(gpte);
+
+ pfn = gfn_to_pfn_atomic(vcpu->kvm, gfn);
+ if (is_error_pfn(pfn)) {
+ kvm_release_pfn_clean(pfn);
+ break;
+ }
+
+ pte_access = sp->role.access & FNAME(gpte_access)(vcpu, gpte);
+ mmu_set_spte(vcpu, spte, sp->role.access, pte_access, 0, 0,
+ is_dirty_gpte(gpte), NULL, sp->role.level, gfn,
+ pfn, true, true);
+ }
+}
+
/*
* Fetch a shadow pte for a specific level in the paging hierarchy.
*/
@@ -401,6 +476,7 @@ check_set_spte:
user_fault, write_fault,
dirty, ptwrite, level,
gw->gfn, pfn, false, true);
+ FNAME(pte_prefetch)(vcpu, sptep);
break;
}
}
--
1.6.1.2



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