KVM: x86/mmu: Use separate namespaces for guest PTEs and shadow PTEs

Separate the macros for KVM's shadow PTEs (SPTE) from guest 64-bit PTEs
(PT64).  SPTE and PT64 are _mostly_ the same, but the few differences are
quite critical, e.g. *_BASE_ADDR_MASK must differentiate between host and
guest physical address spaces, and SPTE_PERM_MASK (was PT64_PERM_MASK) is
very much specific to SPTEs.

Opportunistically (and temporarily) move most guest macros into paging.h
to clearly associate them with shadow paging, and to ensure that they're
not used as of this commit.  A future patch will eliminate them entirely.

Sadly, PT32_LEVEL_BITS is left behind in mmu_internal.h because it's
needed for the quadrant calculation in kvm_mmu_get_page().  The quadrant
calculation is hot enough (when using shadow paging with 32-bit guests)
that adding a per-context helper is undesirable, and burying the
computation in paging_tmpl.h with a forward declaration isn't exactly an
improvement.
Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20220614233328.3896033-6-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/x86/kvm/mmu.h

@@ -6,11 +6,6 @@
 #include "kvm_cache_regs.h"
 #include "cpuid.h"
 
-#define PT64_PT_BITS 9
-#define PT64_ENT_PER_PAGE __PT_ENT_PER_PAGE(PT64_PT_BITS)
-#define PT32_PT_BITS 10
-#define PT32_ENT_PER_PAGE __PT_ENT_PER_PAGE(PT32_PT_BITS)
-
 #define PT_WRITABLE_SHIFT 1
 #define PT_USER_SHIFT 2
 

arch/x86/kvm/mmu/mmu.c

@@ -111,20 +111,6 @@ module_param(dbg, bool, 0644);
 
 #define PTE_PREFETCH_NUM		8
 
-#define PT32_LEVEL_BITS 10
-
-#define PT32_LEVEL_SHIFT(level) __PT_LEVEL_SHIFT(level, PT32_LEVEL_BITS)
-
-#define PT32_LVL_OFFSET_MASK(level) \
-	__PT_LVL_OFFSET_MASK(PT32_BASE_ADDR_MASK, level, PT32_LEVEL_BITS)
-
-#define PT32_INDEX(address, level) __PT_INDEX(address, level, PT32_LEVEL_BITS)
-
-#define PT32_BASE_ADDR_MASK PAGE_MASK
-
-#define PT32_LVL_ADDR_MASK(level) \
-	__PT_LVL_ADDR_MASK(PT32_BASE_ADDR_MASK, level, PT32_LEVEL_BITS)
-
 #include <trace/events/kvm.h>
 
 /* make pte_list_desc fit well in cache lines */
@@ -704,7 +690,7 @@ static gfn_t kvm_mmu_page_get_gfn(struct kvm_mmu_page *sp, int index)
 	if (!sp->role.direct)
 		return sp->gfns[index];
 
-	return sp->gfn + (index << ((sp->role.level - 1) * PT64_LEVEL_BITS));
+	return sp->gfn + (index << ((sp->role.level - 1) * SPTE_LEVEL_BITS));
 }
 
 static void kvm_mmu_page_set_gfn(struct kvm_mmu_page *sp, int index, gfn_t gfn)
@@ -1776,7 +1762,7 @@ static int __mmu_unsync_walk(struct kvm_mmu_page *sp,
 			continue;
 		}
 
-		child = to_shadow_page(ent & PT64_BASE_ADDR_MASK);
+		child = to_shadow_page(ent & SPTE_BASE_ADDR_MASK);
 
 		if (child->unsync_children) {
 			if (mmu_pages_add(pvec, child, i))
@@ -2027,8 +2013,24 @@ static struct kvm_mmu_page *kvm_mmu_get_page(struct kvm_vcpu *vcpu,
 	role.direct = direct;
 	role.access = access;
 	if (role.has_4_byte_gpte) {
-		quadrant = gaddr >> (PAGE_SHIFT + (PT64_PT_BITS * level));
-		quadrant &= (1 << ((PT32_PT_BITS - PT64_PT_BITS) * level)) - 1;
+		/*
+		 * If the guest has 4-byte PTEs then that means it's using 32-bit,
+		 * 2-level, non-PAE paging. KVM shadows such guests with PAE paging
+		 * (i.e. 8-byte PTEs). The difference in PTE size means that KVM must
+		 * shadow each guest page table with multiple shadow page tables, which
+		 * requires extra bookkeeping in the role.
+		 *
+		 * Specifically, to shadow the guest's page directory (which covers a
+		 * 4GiB address space), KVM uses 4 PAE page directories, each mapping
+		 * 1GiB of the address space. @role.quadrant encodes which quarter of
+		 * the address space each maps.
+		 *
+		 * To shadow the guest's page tables (which each map a 4MiB region), KVM
+		 * uses 2 PAE page tables, each mapping a 2MiB region. For these,
+		 * @role.quadrant encodes which half of the region they map.
+		 */
+		quadrant = gaddr >> (PAGE_SHIFT + (SPTE_LEVEL_BITS * level));
+		quadrant &= (1 << level) - 1;
 		role.quadrant = quadrant;
 	}
 	if (level <= vcpu->arch.mmu->cpu_role.base.level)
@@ -2132,7 +2134,7 @@ static void shadow_walk_init_using_root(struct kvm_shadow_walk_iterator *iterato
 
 		iterator->shadow_addr
 			= vcpu->arch.mmu->pae_root[(addr >> 30) & 3];
-		iterator->shadow_addr &= PT64_BASE_ADDR_MASK;
+		iterator->shadow_addr &= SPTE_BASE_ADDR_MASK;
 		--iterator->level;
 		if (!iterator->shadow_addr)
 			iterator->level = 0;
@@ -2151,7 +2153,7 @@ static bool shadow_walk_okay(struct kvm_shadow_walk_iterator *iterator)
 	if (iterator->level < PG_LEVEL_4K)
 		return false;
 
-	iterator->index = SHADOW_PT_INDEX(iterator->addr, iterator->level);
+	iterator->index = SPTE_INDEX(iterator->addr, iterator->level);
 	iterator->sptep	= ((u64 *)__va(iterator->shadow_addr)) + iterator->index;
 	return true;
 }
@@ -2164,7 +2166,7 @@ static void __shadow_walk_next(struct kvm_shadow_walk_iterator *iterator,
 		return;
 	}
 
-	iterator->shadow_addr = spte & PT64_BASE_ADDR_MASK;
+	iterator->shadow_addr = spte & SPTE_BASE_ADDR_MASK;
 	--iterator->level;
 }
 
@@ -2203,7 +2205,7 @@ static void validate_direct_spte(struct kvm_vcpu *vcpu, u64 *sptep,
 		 * so we should update the spte at this point to get
 		 * a new sp with the correct access.
 		 */
-		child = to_shadow_page(*sptep & PT64_BASE_ADDR_MASK);
+		child = to_shadow_page(*sptep & SPTE_BASE_ADDR_MASK);
 		if (child->role.access == direct_access)
 			return;
 
@@ -2224,7 +2226,7 @@ static int mmu_page_zap_pte(struct kvm *kvm, struct kvm_mmu_page *sp,
 		if (is_last_spte(pte, sp->role.level)) {
 			drop_spte(kvm, spte);
 		} else {
-			child = to_shadow_page(pte & PT64_BASE_ADDR_MASK);
+			child = to_shadow_page(pte & SPTE_BASE_ADDR_MASK);
 			drop_parent_pte(child, spte);
 
 			/*
@@ -2250,7 +2252,7 @@ static int kvm_mmu_page_unlink_children(struct kvm *kvm,
 	int zapped = 0;
 	unsigned i;
 
-	for (i = 0; i < PT64_ENT_PER_PAGE; ++i)
+	for (i = 0; i < SPTE_ENT_PER_PAGE; ++i)
 		zapped += mmu_page_zap_pte(kvm, sp, sp->spt + i, invalid_list);
 
 	return zapped;
@@ -2663,7 +2665,7 @@ static int mmu_set_spte(struct kvm_vcpu *vcpu, struct kvm_memory_slot *slot,
 			struct kvm_mmu_page *child;
 			u64 pte = *sptep;
 
-			child = to_shadow_page(pte & PT64_BASE_ADDR_MASK);
+			child = to_shadow_page(pte & SPTE_BASE_ADDR_MASK);
 			drop_parent_pte(child, sptep);
 			flush = true;
 		} else if (pfn != spte_to_pfn(*sptep)) {
@@ -3252,7 +3254,7 @@ static void mmu_free_root_page(struct kvm *kvm, hpa_t *root_hpa,
 	if (!VALID_PAGE(*root_hpa))
 		return;
 
-	sp = to_shadow_page(*root_hpa & PT64_BASE_ADDR_MASK);
+	sp = to_shadow_page(*root_hpa & SPTE_BASE_ADDR_MASK);
 	if (WARN_ON(!sp))
 		return;
 
@@ -3724,7 +3726,7 @@ void kvm_mmu_sync_roots(struct kvm_vcpu *vcpu)
 		hpa_t root = vcpu->arch.mmu->pae_root[i];
 
 		if (IS_VALID_PAE_ROOT(root)) {
-			root &= PT64_BASE_ADDR_MASK;
+			root &= SPTE_BASE_ADDR_MASK;
 			sp = to_shadow_page(root);
 			mmu_sync_children(vcpu, sp, true);
 		}
@@ -5186,11 +5188,11 @@ static bool need_remote_flush(u64 old, u64 new)
 		return false;
 	if (!is_shadow_present_pte(new))
 		return true;
-	if ((old ^ new) & PT64_BASE_ADDR_MASK)
+	if ((old ^ new) & SPTE_BASE_ADDR_MASK)
 		return true;
 	old ^= shadow_nx_mask;
 	new ^= shadow_nx_mask;
-	return (old & ~new & PT64_PERM_MASK) != 0;
+	return (old & ~new & SPTE_PERM_MASK) != 0;
 }
 
 static u64 mmu_pte_write_fetch_gpte(struct kvm_vcpu *vcpu, gpa_t *gpa,

arch/x86/kvm/mmu/paging.h

@@ -5,11 +5,28 @@
 
 #define GUEST_PT64_BASE_ADDR_MASK (((1ULL << 52) - 1) & ~(u64)(PAGE_SIZE-1))
 
+#define PT64_LEVEL_BITS 9
+
+#define PT64_INDEX(address, level) __PT_INDEX(address, level, PT64_LEVEL_BITS)
+
 #define PT64_LVL_ADDR_MASK(level) \
 	__PT_LVL_ADDR_MASK(GUEST_PT64_BASE_ADDR_MASK, level, PT64_LEVEL_BITS)
 
 #define PT64_LVL_OFFSET_MASK(level) \
 	__PT_LVL_OFFSET_MASK(GUEST_PT64_BASE_ADDR_MASK, level, PT64_LEVEL_BITS)
 
+
+#define PT32_LEVEL_SHIFT(level) __PT_LEVEL_SHIFT(level, PT32_LEVEL_BITS)
+
+#define PT32_LVL_OFFSET_MASK(level) \
+	__PT_LVL_OFFSET_MASK(PT32_BASE_ADDR_MASK, level, PT32_LEVEL_BITS)
+
+#define PT32_INDEX(address, level) __PT_INDEX(address, level, PT32_LEVEL_BITS)
+
+#define PT32_BASE_ADDR_MASK PAGE_MASK
+
+#define PT32_LVL_ADDR_MASK(level) \
+	__PT_LVL_ADDR_MASK(PT32_BASE_ADDR_MASK, level, PT32_LEVEL_BITS)
+
 #endif /* __KVM_X86_PAGING_H */
 

arch/x86/kvm/mmu/paging_tmpl.h

@@ -45,7 +45,7 @@
 	#define PT_LVL_ADDR_MASK(lvl) PT32_LVL_ADDR_MASK(lvl)
 	#define PT_LVL_OFFSET_MASK(lvl) PT32_LVL_OFFSET_MASK(lvl)
 	#define PT_INDEX(addr, level) PT32_INDEX(addr, level)
-	#define PT_LEVEL_BITS PT32_LEVEL_BITS
+	#define PT_LEVEL_BITS 10
 	#define PT_MAX_FULL_LEVELS 2
 	#define PT_GUEST_DIRTY_SHIFT PT_DIRTY_SHIFT
 	#define PT_GUEST_ACCESSED_SHIFT PT_ACCESSED_SHIFT
@@ -899,7 +899,7 @@ static gpa_t FNAME(get_level1_sp_gpa)(struct kvm_mmu_page *sp)
 	WARN_ON(sp->role.level != PG_LEVEL_4K);
 
 	if (PTTYPE == 32)
-		offset = sp->role.quadrant << PT64_LEVEL_BITS;
+		offset = sp->role.quadrant << SPTE_LEVEL_BITS;
 
 	return gfn_to_gpa(sp->gfn) + offset * sizeof(pt_element_t);
 }
@@ -1034,7 +1034,7 @@ static int FNAME(sync_page)(struct kvm_vcpu *vcpu, struct kvm_mmu_page *sp)
 
 	first_pte_gpa = FNAME(get_level1_sp_gpa)(sp);
 
-	for (i = 0; i < PT64_ENT_PER_PAGE; i++) {
+	for (i = 0; i < SPTE_ENT_PER_PAGE; i++) {
 		u64 *sptep, spte;
 		struct kvm_memory_slot *slot;
 		unsigned pte_access;

arch/x86/kvm/mmu/spte.c

@@ -301,7 +301,7 @@ u64 kvm_mmu_changed_pte_notifier_make_spte(u64 old_spte, kvm_pfn_t new_pfn)
 {
 	u64 new_spte;
 
-	new_spte = old_spte & ~PT64_BASE_ADDR_MASK;
+	new_spte = old_spte & ~SPTE_BASE_ADDR_MASK;
 	new_spte |= (u64)new_pfn << PAGE_SHIFT;
 
 	new_spte &= ~PT_WRITABLE_MASK;

arch/x86/kvm/mmu/spte.h

@@ -36,12 +36,12 @@ extern bool __read_mostly enable_mmio_caching;
 static_assert(SPTE_TDP_AD_ENABLED_MASK == 0);
 
 #ifdef CONFIG_DYNAMIC_PHYSICAL_MASK
-#define PT64_BASE_ADDR_MASK (physical_mask & ~(u64)(PAGE_SIZE-1))
+#define SPTE_BASE_ADDR_MASK (physical_mask & ~(u64)(PAGE_SIZE-1))
 #else
-#define PT64_BASE_ADDR_MASK (((1ULL << 52) - 1) & ~(u64)(PAGE_SIZE-1))
+#define SPTE_BASE_ADDR_MASK (((1ULL << 52) - 1) & ~(u64)(PAGE_SIZE-1))
 #endif
 
-#define PT64_PERM_MASK (PT_PRESENT_MASK | PT_WRITABLE_MASK | shadow_user_mask \
+#define SPTE_PERM_MASK (PT_PRESENT_MASK | PT_WRITABLE_MASK | shadow_user_mask \
 			| shadow_x_mask | shadow_nx_mask | shadow_me_mask)
 
 #define ACC_EXEC_MASK    1
@@ -50,16 +50,13 @@ static_assert(SPTE_TDP_AD_ENABLED_MASK == 0);
 #define ACC_ALL          (ACC_EXEC_MASK | ACC_WRITE_MASK | ACC_USER_MASK)
 
 /* The mask for the R/X bits in EPT PTEs */
-#define PT64_EPT_READABLE_MASK			0x1ull
-#define PT64_EPT_EXECUTABLE_MASK		0x4ull
+#define SPTE_EPT_READABLE_MASK			0x1ull
+#define SPTE_EPT_EXECUTABLE_MASK		0x4ull
 
-#define PT64_LEVEL_BITS 9
-
-#define PT64_LEVEL_SHIFT(level) __PT_LEVEL_SHIFT(level, PT64_LEVEL_BITS)
-
-#define PT64_INDEX(address, level) __PT_INDEX(address, level, PT64_LEVEL_BITS)
-
-#define SHADOW_PT_INDEX(addr, level) PT64_INDEX(addr, level)
+#define SPTE_LEVEL_BITS			9
+#define SPTE_LEVEL_SHIFT(level)		__PT_LEVEL_SHIFT(level, SPTE_LEVEL_BITS)
+#define SPTE_INDEX(address, level)	__PT_INDEX(address, level, SPTE_LEVEL_BITS)
+#define SPTE_ENT_PER_PAGE		__PT_ENT_PER_PAGE(SPTE_LEVEL_BITS)
 
 /*
  * The mask/shift to use for saving the original R/X bits when marking the PTE
@@ -68,8 +65,8 @@ static_assert(SPTE_TDP_AD_ENABLED_MASK == 0);
  * restored only when a write is attempted to the page.  This mask obviously
  * must not overlap the A/D type mask.
  */
-#define SHADOW_ACC_TRACK_SAVED_BITS_MASK (PT64_EPT_READABLE_MASK | \
-					  PT64_EPT_EXECUTABLE_MASK)
+#define SHADOW_ACC_TRACK_SAVED_BITS_MASK (SPTE_EPT_READABLE_MASK | \
+					  SPTE_EPT_EXECUTABLE_MASK)
 #define SHADOW_ACC_TRACK_SAVED_BITS_SHIFT 54
 #define SHADOW_ACC_TRACK_SAVED_MASK	(SHADOW_ACC_TRACK_SAVED_BITS_MASK << \
 					 SHADOW_ACC_TRACK_SAVED_BITS_SHIFT)
@@ -281,7 +278,7 @@ static inline bool is_executable_pte(u64 spte)
 
 static inline kvm_pfn_t spte_to_pfn(u64 pte)
 {
-	return (pte & PT64_BASE_ADDR_MASK) >> PAGE_SHIFT;
+	return (pte & SPTE_BASE_ADDR_MASK) >> PAGE_SHIFT;
 }
 
 static inline bool is_accessed_spte(u64 spte)

arch/x86/kvm/mmu/tdp_iter.c

@@ -11,7 +11,7 @@
 static void tdp_iter_refresh_sptep(struct tdp_iter *iter)
 {
 	iter->sptep = iter->pt_path[iter->level - 1] +
-		SHADOW_PT_INDEX(iter->gfn << PAGE_SHIFT, iter->level);
+		SPTE_INDEX(iter->gfn << PAGE_SHIFT, iter->level);
 	iter->old_spte = kvm_tdp_mmu_read_spte(iter->sptep);
 }
 
@@ -116,8 +116,8 @@ static bool try_step_side(struct tdp_iter *iter)
 	 * Check if the iterator is already at the end of the current page
 	 * table.
 	 */
-	if (SHADOW_PT_INDEX(iter->gfn << PAGE_SHIFT, iter->level) ==
-            (PT64_ENT_PER_PAGE - 1))
+	if (SPTE_INDEX(iter->gfn << PAGE_SHIFT, iter->level) ==
+	    (SPTE_ENT_PER_PAGE - 1))
 		return false;
 
 	iter->gfn += KVM_PAGES_PER_HPAGE(iter->level);

arch/x86/kvm/mmu/tdp_mmu.c

@@ -425,7 +425,7 @@ static void handle_removed_pt(struct kvm *kvm, tdp_ptep_t pt, bool shared)
 
 	tdp_mmu_unlink_sp(kvm, sp, shared);
 
-	for (i = 0; i < PT64_ENT_PER_PAGE; i++) {
+	for (i = 0; i < SPTE_ENT_PER_PAGE; i++) {
 		tdp_ptep_t sptep = pt + i;
 		gfn_t gfn = base_gfn + i * KVM_PAGES_PER_HPAGE(level);
 		u64 old_spte;
@@ -1477,7 +1477,7 @@ static int tdp_mmu_split_huge_page(struct kvm *kvm, struct tdp_iter *iter,
 	 * No need for atomics when writing to sp->spt since the page table has
 	 * not been linked in yet and thus is not reachable from any other CPU.
 	 */
-	for (i = 0; i < PT64_ENT_PER_PAGE; i++)
+	for (i = 0; i < SPTE_ENT_PER_PAGE; i++)
 		sp->spt[i] = make_huge_page_split_spte(huge_spte, level, i);
 
 	/*
@@ -1497,7 +1497,7 @@ static int tdp_mmu_split_huge_page(struct kvm *kvm, struct tdp_iter *iter,
 	 * are overwriting from the page stats. But we have to manually update
 	 * the page stats with the new present child pages.
 	 */
-	kvm_update_page_stats(kvm, level - 1, PT64_ENT_PER_PAGE);
+	kvm_update_page_stats(kvm, level - 1, SPTE_ENT_PER_PAGE);
 
 out:
 	trace_kvm_mmu_split_huge_page(iter->gfn, huge_spte, level, ret);