From: Peter Feiner <pfeiner@google.com>
Date: Fri, 30 Jun 2017 17:26:29 -0700
Subject: x86: kvm: mmu: dead code thanks to access tracking
Patch-mainline: v4.13-rc1
Git-commit: ce00053b1cfca312c22e2a6465451f1862561eab
References: bsc#1077761

The MMU always has hardware A bits or access tracking support, thus
it's unnecessary to handle the scenario where we have neither.

Signed-off-by: Peter Feiner <pfeiner@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Acked-by: Alexander Graf <agraf@suse.de>
---
 arch/x86/kvm/mmu.c |   30 +++++++++---------------------
 1 file changed, 9 insertions(+), 21 deletions(-)

--- a/arch/x86/kvm/mmu.c
+++ b/arch/x86/kvm/mmu.c
@@ -316,12 +316,21 @@
 	return likely(kvm_gen == spte_gen);
 }
 
+/*
+ * Sets the shadow PTE masks used by the MMU.
+ *
+ * Assumptions:
+ *  - Setting either @accessed_mask or @dirty_mask requires setting both
+ *  - At least one of @accessed_mask or @acc_track_mask must be set
+ */
 void kvm_mmu_set_mask_ptes(u64 user_mask, u64 accessed_mask,
 		u64 dirty_mask, u64 nx_mask, u64 x_mask, u64 p_mask,
 		u64 acc_track_mask)
 {
 	if (acc_track_mask != 0)
 		acc_track_mask |= SPTE_SPECIAL_MASK;
+	BUG_ON(!dirty_mask != !accessed_mask);
+	BUG_ON(!accessed_mask && !acc_track_mask);
 
 	shadow_user_mask = user_mask;
 	shadow_accessed_mask = accessed_mask;
@@ -1768,18 +1777,9 @@
 	u64 *sptep;
 	struct rmap_iterator iter;
 
-	/*
-	 * If there's no access bit in the secondary pte set by the hardware and
-	 * fast access tracking is also not enabled, it's up to gup-fast/gup to
-	 * set the access bit in the primary pte or in the page structure.
-	 */
-	if (!shadow_accessed_mask && !shadow_acc_track_mask)
-		goto out;
-
 	for_each_rmap_spte(rmap_head, &iter, sptep)
 		if (is_accessed_spte(*sptep))
 			return 1;
-out:
 	return 0;
 }
 
@@ -1800,18 +1800,6 @@
 
 int kvm_age_hva(struct kvm *kvm, unsigned long start, unsigned long end)
 {
-	/*
-	 * In case of absence of EPT Access and Dirty Bits supports,
-	 * emulate the accessed bit for EPT, by checking if this page has
-	 * an EPT mapping, and clearing it if it does. On the next access,
-	 * a new EPT mapping will be established.
-	 * This has some overhead, but not as much as the cost of swapping
-	 * out actively used pages or breaking up actively used hugepages.
-	 */
-	if (!shadow_accessed_mask && !shadow_acc_track_mask)
-		return kvm_handle_hva_range(kvm, start, end, 0,
-					    kvm_unmap_rmapp);
-
 	return kvm_handle_hva_range(kvm, start, end, 0, kvm_age_rmapp);
 }