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

[Vitaly Kuznetsov <vkuznets@xxxxxxxxxx>]

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