[PATCH] LoongArch: KVM: Optimization for memslot hugepage checking

[Bibo Mao]

During shadow mmu page fault, there is checking for huge page for
specified memslot. Page fault is hot path, check logic can be done
when memslot is created. Here two flags are added for huge page
checking, KVM_MEM_HUGEPAGE_CAPABLE and KVM_MEM_HUGEPAGE_INCAPABLE.
Instead for optimization qemu, memslot for dram is always huge page
aligned. The flag is firstly checked during hot page fault path.

Now only huge page flag is supported, there is a long way for super
page support in LoongArch system. Since super page size is 64G for
16K pagesize and 1G for 4K pagesize, 64G physical address is rarely
used and LoongArch kernel needs support super page for 4K. Also memory
layout of LoongArch qemu VM should be 1G aligned.

Signed-off-by: Bibo Mao <maobibo@xxxxxxxxxxx>
---
 arch/loongarch/include/asm/kvm_host.h |   3 +
 arch/loongarch/kvm/mmu.c              | 127 +++++++++++++++++---------
 2 files changed, 89 insertions(+), 41 deletions(-)

diff --git a/arch/loongarch/include/asm/kvm_host.h b/arch/loongarch/include/asm/kvm_host.h
index 11328700d4fa..0e89db020481 100644
--- a/arch/loongarch/include/asm/kvm_host.h
+++ b/arch/loongarch/include/asm/kvm_host.h
@@ -45,7 +45,10 @@ struct kvm_vcpu_stat {
 	u64 signal_exits;
 };
 
+#define KVM_MEM_HUGEPAGE_CAPABLE	(1UL << 0)
+#define KVM_MEM_HUGEPAGE_INCAPABLE	(1UL << 1)
 struct kvm_arch_memory_slot {
+	unsigned long flags;
 };
 
 struct kvm_context {
diff --git a/arch/loongarch/kvm/mmu.c b/arch/loongarch/kvm/mmu.c
index 80480df5f550..6845733f37dc 100644
--- a/arch/loongarch/kvm/mmu.c
+++ b/arch/loongarch/kvm/mmu.c
@@ -13,6 +13,16 @@
 #include <asm/tlb.h>
 #include <asm/kvm_mmu.h>
 
+static inline bool kvm_hugepage_capable(struct kvm_memory_slot *slot)
+{
+	return slot->arch.flags & KVM_MEM_HUGEPAGE_CAPABLE;
+}
+
+static inline bool kvm_hugepage_incapable(struct kvm_memory_slot *slot)
+{
+	return slot->arch.flags & KVM_MEM_HUGEPAGE_INCAPABLE;
+}
+
 static inline void kvm_ptw_prepare(struct kvm *kvm, kvm_ptw_ctx *ctx)
 {
 	ctx->level = kvm->arch.root_level;
@@ -365,6 +375,71 @@ void kvm_arch_mmu_enable_log_dirty_pt_masked(struct kvm *kvm,
 	kvm_ptw_top(kvm->arch.pgd, start << PAGE_SHIFT, end << PAGE_SHIFT, &ctx);
 }
 
+int kvm_arch_prepare_memory_region(struct kvm *kvm,
+				const struct kvm_memory_slot *old,
+				struct kvm_memory_slot *new,
+				enum kvm_mr_change change)
+{
+	size_t size, gpa_offset, hva_offset;
+	gpa_t gpa_start;
+	hva_t hva_start;
+
+	if ((change != KVM_MR_MOVE) && (change != KVM_MR_CREATE))
+		return 0;
+	/*
+	 * Prevent userspace from creating a memory region outside of the
+	 * VM GPA address space
+	 */
+	if ((new->base_gfn + new->npages) > (kvm->arch.gpa_size >> PAGE_SHIFT))
+		return -ENOMEM;
+
+	size = new->npages * PAGE_SIZE;
+	gpa_start = new->base_gfn << PAGE_SHIFT;
+	hva_start = new->userspace_addr;
+	new->arch.flags = 0;
+	if (IS_ALIGNED(size, PMD_SIZE) && IS_ALIGNED(gpa_start, PMD_SIZE)
+			&& IS_ALIGNED(hva_start, PMD_SIZE))
+		new->arch.flags |= KVM_MEM_HUGEPAGE_CAPABLE;
+	else {
+		/*
+		 * Pages belonging to memslots that don't have the same
+		 * alignment within a PMD for userspace and GPA cannot be
+		 * mapped with PMD entries, because we'll end up mapping
+		 * the wrong pages.
+		 *
+		 * Consider a layout like the following:
+		 *
+		 *    memslot->userspace_addr:
+		 *    +-----+--------------------+--------------------+---+
+		 *    |abcde|fgh  Stage-1 block  |    Stage-1 block tv|xyz|
+		 *    +-----+--------------------+--------------------+---+
+		 *
+		 *    memslot->base_gfn << PAGE_SIZE:
+		 *      +---+--------------------+--------------------+-----+
+		 *      |abc|def  Stage-2 block  |    Stage-2 block   |tvxyz|
+		 *      +---+--------------------+--------------------+-----+
+		 *
+		 * If we create those stage-2 blocks, we'll end up with this
+		 * incorrect mapping:
+		 *   d -> f
+		 *   e -> g
+		 *   f -> h
+		 */
+		gpa_offset = gpa_start & (PMD_SIZE - 1);
+		hva_offset = hva_start & (PMD_SIZE - 1);
+		if (gpa_offset != hva_offset) {
+			new->arch.flags |= KVM_MEM_HUGEPAGE_INCAPABLE;
+		} else {
+			if (gpa_offset == 0)
+				gpa_offset = PMD_SIZE;
+			if ((size + gpa_offset) < (PMD_SIZE * 2))
+				new->arch.flags |= KVM_MEM_HUGEPAGE_INCAPABLE;
+		}
+	}
+
+	return 0;
+}
+
 void kvm_arch_commit_memory_region(struct kvm *kvm,
 				   struct kvm_memory_slot *old,
 				   const struct kvm_memory_slot *new,
@@ -562,47 +637,23 @@ static int kvm_map_page_fast(struct kvm_vcpu *vcpu, unsigned long gpa, bool writ
 }
 
 static bool fault_supports_huge_mapping(struct kvm_memory_slot *memslot,
-				unsigned long hva, unsigned long map_size, bool write)
+				unsigned long hva, bool write)
 {
-	size_t size;
-	gpa_t gpa_start;
-	hva_t uaddr_start, uaddr_end;
+	hva_t start, end;
 
 	/* Disable dirty logging on HugePages */
 	if (kvm_slot_dirty_track_enabled(memslot) && write)
 		return false;
 
-	size = memslot->npages * PAGE_SIZE;
-	gpa_start = memslot->base_gfn << PAGE_SHIFT;
-	uaddr_start = memslot->userspace_addr;
-	uaddr_end = uaddr_start + size;
+	if (kvm_hugepage_capable(memslot))
+		return true;
 
-	/*
-	 * Pages belonging to memslots that don't have the same alignment
-	 * within a PMD for userspace and GPA cannot be mapped with stage-2
-	 * PMD entries, because we'll end up mapping the wrong pages.
-	 *
-	 * Consider a layout like the following:
-	 *
-	 *    memslot->userspace_addr:
-	 *    +-----+--------------------+--------------------+---+
-	 *    |abcde|fgh  Stage-1 block  |    Stage-1 block tv|xyz|
-	 *    +-----+--------------------+--------------------+---+
-	 *
-	 *    memslot->base_gfn << PAGE_SIZE:
-	 *      +---+--------------------+--------------------+-----+
-	 *      |abc|def  Stage-2 block  |    Stage-2 block   |tvxyz|
-	 *      +---+--------------------+--------------------+-----+
-	 *
-	 * If we create those stage-2 blocks, we'll end up with this incorrect
-	 * mapping:
-	 *   d -> f
-	 *   e -> g
-	 *   f -> h
-	 */
-	if ((gpa_start & (map_size - 1)) != (uaddr_start & (map_size - 1)))
+	if (kvm_hugepage_incapable(memslot))
 		return false;
 
+	start = memslot->userspace_addr;
+	end = start + memslot->npages * PAGE_SIZE;
+
 	/*
 	 * Next, let's make sure we're not trying to map anything not covered
 	 * by the memslot. This means we have to prohibit block size mappings
@@ -615,8 +666,8 @@ static bool fault_supports_huge_mapping(struct kvm_memory_slot *memslot,
 	 * userspace_addr or the base_gfn, as both are equally aligned (per
 	 * the check above) and equally sized.
 	 */
-	return (hva & ~(map_size - 1)) >= uaddr_start &&
-		(hva & ~(map_size - 1)) + map_size <= uaddr_end;
+	return (hva >= ALIGN(start, PMD_SIZE)) &&
+			(hva < ALIGN_DOWN(end, PMD_SIZE));
 }
 
 /*
@@ -842,7 +893,7 @@ static int kvm_map_page(struct kvm_vcpu *vcpu, unsigned long gpa, bool write)
 
 	/* Disable dirty logging on HugePages */
 	level = 0;
-	if (!fault_supports_huge_mapping(memslot, hva, PMD_SIZE, write)) {
+	if (!fault_supports_huge_mapping(memslot, hva, write)) {
 		level = 0;
 	} else {
 		level = host_pfn_mapping_level(kvm, gfn, memslot);
@@ -901,12 +952,6 @@ void kvm_arch_sync_dirty_log(struct kvm *kvm, struct kvm_memory_slot *memslot)
 {
 }
 
-int kvm_arch_prepare_memory_region(struct kvm *kvm, const struct kvm_memory_slot *old,
-				   struct kvm_memory_slot *new, enum kvm_mr_change change)
-{
-	return 0;
-}
-
 void kvm_arch_flush_remote_tlbs_memslot(struct kvm *kvm,
 					const struct kvm_memory_slot *memslot)
 {
-- 
2.39.3