x86: kvm: mmu: dead code thanks to access tracking

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>

diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
index 5d3376f..dfd4cd6 100644 (file)
--- a/arch/x86/kvm/mmu.c
+++ b/arch/x86/kvm/mmu.c
@@ -315,12 +315,21 @@ static bool check_mmio_spte(struct kvm_vcpu *vcpu, u64 spte)
        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;
@@ -1766,18 +1775,9 @@ static int kvm_test_age_rmapp(struct kvm *kvm, struct kvm_rmap_head *rmap_head,
        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;
 }
 
@@ -1798,18 +1798,6 @@ static void rmap_recycle(struct kvm_vcpu *vcpu, u64 *spte, gfn_t gfn)
 
 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);
 }