KVM: x86/mmu: Rely on host page tables to find HugeTLB mappings

Remove KVM's HugeTLB specific logic and instead rely on walking the host
page tables (already done for THP) to identify HugeTLB mappings.
Eliminating the HugeTLB-only logic avoids taking mmap_sem and calling
find_vma() for all hugepage compatible page faults, and simplifies KVM's
page fault code by consolidating all hugepage adjustments into a common
helper.
Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/x86/kvm/mmu/mmu.c

@@ -1286,23 +1286,6 @@ static bool mmu_gfn_lpage_is_disallowed(struct kvm_vcpu *vcpu, gfn_t gfn,
 	return __mmu_gfn_lpage_is_disallowed(gfn, level, slot);
 }
 
-static int host_mapping_level(struct kvm_vcpu *vcpu, gfn_t gfn)
-{
-	unsigned long page_size;
-	int i, ret = 0;
-
-	page_size = kvm_host_page_size(vcpu, gfn);
-
-	for (i = PT_PAGE_TABLE_LEVEL; i <= PT_MAX_HUGEPAGE_LEVEL; ++i) {
-		if (page_size >= KVM_HPAGE_SIZE(i))
-			ret = i;
-		else
-			break;
-	}
-
-	return ret;
-}
-
 static inline bool memslot_valid_for_gpte(struct kvm_memory_slot *slot,
 					  bool no_dirty_log)
 {
@@ -1327,43 +1310,25 @@ gfn_to_memslot_dirty_bitmap(struct kvm_vcpu *vcpu, gfn_t gfn,
 	return slot;
 }
 
-static int mapping_level(struct kvm_vcpu *vcpu, gfn_t large_gfn,
-			 int *max_levelp)
+static int max_mapping_level(struct kvm_vcpu *vcpu, gfn_t gfn,
+			     int max_level)
 {
-	int host_level, max_level = *max_levelp;
 	struct kvm_memory_slot *slot;
 
 	if (unlikely(max_level == PT_PAGE_TABLE_LEVEL))
 		return PT_PAGE_TABLE_LEVEL;
 
-	slot = kvm_vcpu_gfn_to_memslot(vcpu, large_gfn);
-	if (!memslot_valid_for_gpte(slot, true)) {
-		*max_levelp = PT_PAGE_TABLE_LEVEL;
+	slot = kvm_vcpu_gfn_to_memslot(vcpu, gfn);
+	if (!memslot_valid_for_gpte(slot, true))
 		return PT_PAGE_TABLE_LEVEL;
-	}
 
 	max_level = min(max_level, kvm_x86_ops->get_lpage_level());
 	for ( ; max_level > PT_PAGE_TABLE_LEVEL; max_level--) {
-		if (!__mmu_gfn_lpage_is_disallowed(large_gfn, max_level, slot))
+		if (!__mmu_gfn_lpage_is_disallowed(gfn, max_level, slot))
 			break;
 	}
 
-	*max_levelp = max_level;
-
-	if (max_level == PT_PAGE_TABLE_LEVEL)
-		return PT_PAGE_TABLE_LEVEL;
-
-	/*
-	 * Note, host_mapping_level() does *not* handle transparent huge pages.
-	 * As suggested by "mapping", it reflects the page size established by
-	 * the associated vma, if there is one, i.e. host_mapping_level() will
-	 * return a huge page level if and only if a vma exists and the backing
-	 * implementation for the vma uses huge pages, e.g. hugetlbfs and dax.
-	 * So, do not propagate host_mapping_level() to max_level as KVM can
-	 * still promote the guest mapping to a huge page in the THP case.
-	 */
-	host_level = host_mapping_level(vcpu, large_gfn);
-	return min(host_level, max_level);
+	return max_level;
 }
 
 /*
@@ -3137,7 +3102,7 @@ static int set_spte(struct kvm_vcpu *vcpu, u64 *sptep,
 
 		/*
 		 * Other vcpu creates new sp in the window between
-		 * mapping_level() and acquiring mmu-lock. We can
+		 * max_mapping_level() and acquiring mmu-lock. We can
 		 * allow guest to retry the access, the mapping can
 		 * be fixed if guest refault.
 		 */
@@ -3357,24 +3322,23 @@ static int host_pfn_mapping_level(struct kvm_vcpu *vcpu, gfn_t gfn,
 	return level;
 }
 
-static void transparent_hugepage_adjust(struct kvm_vcpu *vcpu, gfn_t gfn,
-					int max_level, kvm_pfn_t *pfnp,
-					int *levelp)
+static int kvm_mmu_hugepage_adjust(struct kvm_vcpu *vcpu, gfn_t gfn,
+				   int max_level, kvm_pfn_t *pfnp)
 {
 	kvm_pfn_t pfn = *pfnp;
-	int level = *levelp;
 	kvm_pfn_t mask;
+	int level;
 
-	if (max_level == PT_PAGE_TABLE_LEVEL || level > PT_PAGE_TABLE_LEVEL)
-		return;
+	if (max_level == PT_PAGE_TABLE_LEVEL)
+		return PT_PAGE_TABLE_LEVEL;
 
 	if (is_error_noslot_pfn(pfn) || kvm_is_reserved_pfn(pfn) ||
 	    kvm_is_zone_device_pfn(pfn))
-		return;
+		return PT_PAGE_TABLE_LEVEL;
 
 	level = host_pfn_mapping_level(vcpu, gfn, pfn);
 	if (level == PT_PAGE_TABLE_LEVEL)
-		return;
+		return level;
 
 	level = min(level, max_level);
 
@@ -3382,10 +3346,11 @@ static void transparent_hugepage_adjust(struct kvm_vcpu *vcpu, gfn_t gfn,
 	 * mmu_notifier_retry() was successful and mmu_lock is held, so
 	 * the pmd can't be split from under us.
 	 */
-	*levelp = level;
 	mask = KVM_PAGES_PER_HPAGE(level) - 1;
 	VM_BUG_ON((gfn & mask) != (pfn & mask));
 	*pfnp = pfn & ~mask;
+
+	return level;
 }
 
 static void disallowed_hugepage_adjust(struct kvm_shadow_walk_iterator it,
@@ -3412,20 +3377,19 @@ static void disallowed_hugepage_adjust(struct kvm_shadow_walk_iterator it,
 }
 
 static int __direct_map(struct kvm_vcpu *vcpu, gpa_t gpa, int write,
-			int map_writable, int level, int max_level,
-			kvm_pfn_t pfn, bool prefault,
-			bool account_disallowed_nx_lpage)
+			int map_writable, int max_level, kvm_pfn_t pfn,
+			bool prefault, bool account_disallowed_nx_lpage)
 {
 	struct kvm_shadow_walk_iterator it;
 	struct kvm_mmu_page *sp;
-	int ret;
+	int level, ret;
 	gfn_t gfn = gpa >> PAGE_SHIFT;
 	gfn_t base_gfn = gfn;
 
 	if (WARN_ON(!VALID_PAGE(vcpu->arch.mmu->root_hpa)))
 		return RET_PF_RETRY;
 
-	transparent_hugepage_adjust(vcpu, gfn, max_level, &pfn, &level);
+	level = kvm_mmu_hugepage_adjust(vcpu, gfn, max_level, &pfn);
 
 	trace_kvm_mmu_spte_requested(gpa, level, pfn);
 	for_each_shadow_entry(vcpu, gpa, it) {
@@ -4201,7 +4165,7 @@ static int direct_page_fault(struct kvm_vcpu *vcpu, gpa_t gpa, u32 error_code,
 	gfn_t gfn = gpa >> PAGE_SHIFT;
 	unsigned long mmu_seq;
 	kvm_pfn_t pfn;
-	int level, r;
+	int r;
 
 	if (page_fault_handle_page_track(vcpu, error_code, gfn))
 		return RET_PF_EMULATE;
@@ -4213,9 +4177,7 @@ static int direct_page_fault(struct kvm_vcpu *vcpu, gpa_t gpa, u32 error_code,
 	if (lpage_disallowed)
 		max_level = PT_PAGE_TABLE_LEVEL;
 
-	level = mapping_level(vcpu, gfn, &max_level);
-	if (level > PT_PAGE_TABLE_LEVEL)
-		gfn &= ~(KVM_PAGES_PER_HPAGE(level) - 1);
+	max_level = max_mapping_level(vcpu, gfn, max_level);
 
 	if (fast_page_fault(vcpu, gpa, error_code))
 		return RET_PF_RETRY;
@@ -4235,7 +4197,7 @@ 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, level, max_level, pfn,
+	r = __direct_map(vcpu, gpa, write, map_writable, max_level, pfn,
 			 prefault, is_tdp && lpage_disallowed);
 
 out_unlock:

arch/x86/kvm/mmu/paging_tmpl.h

@@ -628,14 +628,14 @@ static void FNAME(pte_prefetch)(struct kvm_vcpu *vcpu, struct guest_walker *gw,
  */
 static int FNAME(fetch)(struct kvm_vcpu *vcpu, gpa_t addr,
 			 struct guest_walker *gw,
-			 int write_fault, int hlevel, int max_level,
+			 int write_fault, int max_level,
 			 kvm_pfn_t pfn, bool map_writable, bool prefault,
 			 bool lpage_disallowed)
 {
 	struct kvm_mmu_page *sp = NULL;
 	struct kvm_shadow_walk_iterator it;
 	unsigned direct_access, access = gw->pt_access;
-	int top_level, ret;
+	int top_level, hlevel, ret;
 	gfn_t gfn, base_gfn;
 
 	direct_access = gw->pte_access;
@@ -688,7 +688,7 @@ static int FNAME(fetch)(struct kvm_vcpu *vcpu, gpa_t addr,
 	gfn = gw->gfn | ((addr & PT_LVL_OFFSET_MASK(gw->level)) >> PAGE_SHIFT);
 	base_gfn = gfn;
 
-	transparent_hugepage_adjust(vcpu, gw->gfn, max_level, &pfn, &hlevel);
+	hlevel = kvm_mmu_hugepage_adjust(vcpu, gw->gfn, max_level, &pfn);
 
 	trace_kvm_mmu_spte_requested(addr, gw->level, pfn);
 
@@ -790,7 +790,6 @@ static int FNAME(page_fault)(struct kvm_vcpu *vcpu, gpa_t addr, u32 error_code,
 	struct guest_walker walker;
 	int r;
 	kvm_pfn_t pfn;
-	int level;
 	unsigned long mmu_seq;
 	bool map_writable, is_self_change_mapping;
 	bool lpage_disallowed = (error_code & PFERR_FETCH_MASK) &&
@@ -840,9 +839,7 @@ static int FNAME(page_fault)(struct kvm_vcpu *vcpu, gpa_t addr, u32 error_code,
 	else
 		max_level = walker.level;
 
-	level = mapping_level(vcpu, walker.gfn, &max_level);
-	if (level > PT_PAGE_TABLE_LEVEL)
-		walker.gfn = walker.gfn & ~(KVM_PAGES_PER_HPAGE(level) - 1);
+	max_level = max_mapping_level(vcpu, walker.gfn, max_level);
 
 	mmu_seq = vcpu->kvm->mmu_notifier_seq;
 	smp_rmb();
@@ -882,8 +879,8 @@ 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, level, max_level,
-			 pfn, map_writable, prefault, lpage_disallowed);
+	r = FNAME(fetch)(vcpu, addr, &walker, write_fault, max_level, pfn,
+			 map_writable, prefault, lpage_disallowed);
 	kvm_mmu_audit(vcpu, AUDIT_POST_PAGE_FAULT);
 
 out_unlock: