[PATCH RFC 4/5] KVM: x86: aggressively map PTEs in KVM_MEM_ALLONES slots

From: Vitaly Kuznetsov
Date: Thu May 14 2020 - 14:06:13 EST


All PTEs in KVM_MEM_ALLONES slots point to the same read-only page
in KVM so instead of mapping each page upon first access we can map
everything aggressively.

Suggested-by: Michael S. Tsirkin <mst@xxxxxxxxxx>
Signed-off-by: Vitaly Kuznetsov <vkuznets@xxxxxxxxxx>
---
arch/x86/kvm/mmu/mmu.c | 20 ++++++++++++++++++--
arch/x86/kvm/mmu/paging_tmpl.h | 23 +++++++++++++++++++++--
2 files changed, 39 insertions(+), 4 deletions(-)

diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index 3db499df2dfc..e92ca9ed3ff5 100644
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -4154,8 +4154,24 @@ static int direct_page_fault(struct kvm_vcpu *vcpu, gpa_t gpa, u32 error_code,
goto out_unlock;
if (make_mmu_pages_available(vcpu) < 0)
goto out_unlock;
- r = __direct_map(vcpu, gpa, write, map_writable, max_level, pfn,
- prefault, is_tdp && lpage_disallowed);
+
+ if (likely(!(slot->flags & KVM_MEM_ALLONES) || write)) {
+ r = __direct_map(vcpu, gpa, write, map_writable, max_level, pfn,
+ prefault, is_tdp && lpage_disallowed);
+ } else {
+ /*
+ * KVM_MEM_ALLONES are 4k only slots fully mapped to the same
+ * readonly 'allones' page, map all PTEs aggressively here.
+ */
+ for (gfn = slot->base_gfn; gfn < slot->base_gfn + slot->npages;
+ gfn++) {
+ r = __direct_map(vcpu, gfn << PAGE_SHIFT, write,
+ map_writable, max_level, pfn, prefault,
+ is_tdp && lpage_disallowed);
+ if (r)
+ break;
+ }
+ }

out_unlock:
spin_unlock(&vcpu->kvm->mmu_lock);
diff --git a/arch/x86/kvm/mmu/paging_tmpl.h b/arch/x86/kvm/mmu/paging_tmpl.h
index 98e368788e8b..7bf0c48b858f 100644
--- a/arch/x86/kvm/mmu/paging_tmpl.h
+++ b/arch/x86/kvm/mmu/paging_tmpl.h
@@ -789,6 +789,7 @@ static int FNAME(page_fault)(struct kvm_vcpu *vcpu, gpa_t addr, u32 error_code,
bool lpage_disallowed = (error_code & PFERR_FETCH_MASK) &&
is_nx_huge_page_enabled();
int max_level;
+ gfn_t gfn;

pgprintk("%s: addr %lx err %x\n", __func__, addr, error_code);

@@ -873,8 +874,26 @@ static int FNAME(page_fault)(struct kvm_vcpu *vcpu, gpa_t addr, u32 error_code,
kvm_mmu_audit(vcpu, AUDIT_PRE_PAGE_FAULT);
if (make_mmu_pages_available(vcpu) < 0)
goto out_unlock;
- r = FNAME(fetch)(vcpu, addr, &walker, write_fault, max_level, pfn,
- map_writable, prefault, lpage_disallowed);
+ if (likely(!(slot->flags & KVM_MEM_ALLONES) || write_fault)) {
+ r = FNAME(fetch)(vcpu, addr, &walker, write_fault, max_level,
+ pfn, map_writable, prefault, lpage_disallowed);
+ } else {
+ /*
+ * KVM_MEM_ALLONES are 4k only slots fully mapped to the same
+ * readonly 'allones' page, map all PTEs aggressively here.
+ */
+ for (gfn = slot->base_gfn; gfn < slot->base_gfn + slot->npages;
+ gfn++) {
+ walker.gfn = gfn;
+ r = FNAME(fetch)(vcpu, gfn << PAGE_SHIFT, &walker,
+ write_fault, max_level, pfn,
+ map_writable, prefault,
+ lpage_disallowed);
+ if (r)
+ break;
+ }
+ }
+
kvm_mmu_audit(vcpu, AUDIT_POST_PAGE_FAULT);

out_unlock:
--
2.25.4