[PATCH 4/4] KVM: x86/mmu: Use the generic auto-prefaulting to do prefetch for direct MMUs

[Sean Christopherson <seanjc@google.com>]

Use generic auto-prefaulting for direct shadow MMUs and drop the small bit
of custom prefetching that is unique to direct MMUs.  Direct shadow MMUs
are basically on life support, and the generic approach provides comparable
performance, plus it supported guest_memfd and PFN-backed memory.

Note!  Deliberately keep the core direct PTE prefetching logic, as it's
still needed to prefetch PTEs for direct shadow pages in indirect MMUs,
i.e. when the guest is using hugepages but KVM is not.

Opportunistically drop the double-underscores from direct_pte_prefetch()
now that only the version used by indirect MMUs exists.

Signed-off-by: Sean Christopherson <seanjc@google.com>
---
 arch/x86/kvm/mmu/mmu.c         | 48 ++++++----------------------------
 arch/x86/kvm/mmu/paging_tmpl.h |  2 +-
 2 files changed, 9 insertions(+), 41 deletions(-)

diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index c56a2eaa4646..7f8beb1b307b 100644
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -123,8 +123,8 @@ static int tdp_root_level __read_mostly;
 static int max_tdp_level __read_mostly;
 
 /*
- * The exact number of PTEs that can be prefetched for the shadow MMU, and the
- * default number of pages to prefault/prefetch pages for the TDP MMU.
+ * The exact number of PTEs that can be prefetched for indirect MMUs, and the
+ * default number of pages to prefault/prefetch pages for direct MMUs.
  */
 #define PTE_PREFETCH_NUM		8
 
@@ -3275,8 +3275,8 @@ static bool direct_pte_prefetch_many(struct kvm_vcpu *vcpu,
 	return kvm_mmu_prefetch_sptes(vcpu, gfn, start, end - start, access);
 }
 
-static void __direct_pte_prefetch(struct kvm_vcpu *vcpu,
-				  struct kvm_mmu_page *sp, u64 *sptep)
+static void direct_pte_prefetch(struct kvm_vcpu *vcpu, struct kvm_mmu_page *sp,
+				u64 *sptep)
 {
 	u64 *spte, *start = NULL;
 	int i;
@@ -3301,33 +3301,6 @@ static void __direct_pte_prefetch(struct kvm_vcpu *vcpu,
 		direct_pte_prefetch_many(vcpu, sp, start, spte);
 }
 
-static void direct_pte_prefetch(struct kvm_vcpu *vcpu, u64 *sptep)
-{
-	struct kvm_mmu_page *sp;
-
-	sp = sptep_to_sp(sptep);
-
-	/*
-	 * Without accessed bits, there's no way to distinguish between
-	 * actually accessed translations and prefetched, so disable pte
-	 * prefetch if accessed bits aren't available.
-	 */
-	if (sp_ad_disabled(sp))
-		return;
-
-	if (sp->role.level > PG_LEVEL_4K)
-		return;
-
-	/*
-	 * If addresses are being invalidated, skip prefetching to avoid
-	 * accidentally prefetching those addresses.
-	 */
-	if (unlikely(vcpu->kvm->mmu_invalidate_in_progress))
-		return;
-
-	__direct_pte_prefetch(vcpu, sp, sptep);
-}
-
 /*
  * Lookup the mapping level for @gfn in the current mm.
  *
@@ -3562,8 +3535,8 @@ static int direct_map(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault)
 {
 	struct kvm_shadow_walk_iterator it;
 	struct kvm_mmu_page *sp;
-	int ret, access;
 	gfn_t base_gfn = fault->gfn;
+	int access;
 
 	kvm_mmu_hugepage_adjust(vcpu, fault);
 
@@ -3594,13 +3567,8 @@ static int direct_map(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault)
 	if (KVM_BUG_ON(it.level != fault->goal_level, vcpu->kvm))
 		return -EIO;
 
-	ret = mmu_set_spte(vcpu, fault->slot, it.sptep, access,
-			   base_gfn, fault->pfn, fault);
-	if (ret == RET_PF_SPURIOUS)
-		return ret;
-
-	direct_pte_prefetch(vcpu, it.sptep);
-	return ret;
+	return mmu_set_spte(vcpu, fault->slot, it.sptep, access, base_gfn,
+			    fault->pfn, fault);
 }
 
 static void kvm_send_hwpoison_signal(struct kvm_memory_slot *slot, gfn_t gfn)
@@ -6685,7 +6653,7 @@ static void kvm_mmu_auto_prefault(struct kvm_vcpu *vcpu, gpa_t start,
 	if (error_code & (PFERR_RSVD_MASK | PFERR_PRESENT_MASK))
 		return;
 
-	if (!tdp_mmu_enabled || vcpu->arch.mmu->page_fault != kvm_tdp_page_fault)
+	if (vcpu->arch.mmu->page_fault != kvm_tdp_page_fault)
 		return;
 
 	nr_pages = min(nr_pages, KVM_PAGES_PER_HPAGE(PG_LEVEL_1G));
diff --git a/arch/x86/kvm/mmu/paging_tmpl.h b/arch/x86/kvm/mmu/paging_tmpl.h
index 8e350095508c..baaab791f107 100644
--- a/arch/x86/kvm/mmu/paging_tmpl.h
+++ b/arch/x86/kvm/mmu/paging_tmpl.h
@@ -631,7 +631,7 @@ static void FNAME(pte_prefetch)(struct kvm_vcpu *vcpu, struct guest_walker *gw,
 		return;
 
 	if (sp->role.direct)
-		return __direct_pte_prefetch(vcpu, sp, sptep);
+		return direct_pte_prefetch(vcpu, sp, sptep);
 
 	i = spte_index(sptep) & ~(PTE_PREFETCH_NUM - 1);
 	spte = sp->spt + i;
-- 
2.56.0.313.g2479322e68-goog