Message-Id: <20230214025648.1898508-15-zhaotianrui@loongson.cn>
Date:   Tue, 14 Feb 2023 10:56:38 +0800
From:   Tianrui Zhao <zhaotianrui@...ngson.cn>
To:     Paolo Bonzini <pbonzini@...hat.com>
Cc:     Huacai Chen <chenhuacai@...nel.org>,
        WANG Xuerui <kernel@...0n.name>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        loongarch@...ts.linux.dev, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org, Jens Axboe <axboe@...nel.dk>,
        Mark Brown <broonie@...nel.org>,
        Alex Deucher <alexander.deucher@....com>
Subject: [PATCH v1 14/24] LoongArch: KVM: Implement kvm mmu operations

Implement loongarch kvm mmu, it is used to switch gpa to hpa when
guest exit because of address translation exception. This patch
implement allocate gpa page table, search gpa from it and flush guest
gpa in the table.

Signed-off-by: Tianrui Zhao <zhaotianrui@...ngson.cn>
---
 arch/loongarch/kvm/mmu.c | 821 +++++++++++++++++++++++++++++++++++++++
 1 file changed, 821 insertions(+)
 create mode 100644 arch/loongarch/kvm/mmu.c

diff --git a/arch/loongarch/kvm/mmu.c b/arch/loongarch/kvm/mmu.c
new file mode 100644
index 000000000..049824f8e
--- /dev/null
+++ b/arch/loongarch/kvm/mmu.c
@@ -0,0 +1,821 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) 2020-2023 Loongson Technology Corporation Limited
+ */
+
+#include <linux/highmem.h>
+#include <linux/hugetlb.h>
+#include <linux/page-flags.h>
+#include <linux/kvm_host.h>
+#include <linux/uaccess.h>
+#include <asm/kvm_host.h>
+#include <asm/mmu_context.h>
+#include <asm/pgalloc.h>
+#include <asm/tlb.h>
+
+/*
+ * KVM_MMU_CACHE_MIN_PAGES is the number of GPA page table translation levels
+ * for which pages need to be cached.
+ */
+#if defined(__PAGETABLE_PMD_FOLDED)
+#define KVM_MMU_CACHE_MIN_PAGES 1
+#else
+#define KVM_MMU_CACHE_MIN_PAGES 2
+#endif
+
+/**
+ * kvm_pgd_alloc() - Allocate and initialise a KVM GPA page directory.
+ *
+ * Allocate a blank KVM GPA page directory (PGD) for representing guest physical
+ * to host physical page mappings.
+ *
+ * Returns:	Pointer to new KVM GPA page directory.
+ *		NULL on allocation failure.
+ */
+pgd_t *kvm_pgd_alloc(void)
+{
+	pgd_t *pgd;
+
+	pgd = (pgd_t *)__get_free_pages(GFP_KERNEL, 0);
+	if (pgd)
+		pgd_init((void *)pgd);
+
+	return pgd;
+}
+
+/**
+ * kvm_walk_pgd() - Walk page table with optional allocation.
+ * @pgd:	Page directory pointer.
+ * @addr:	Address to index page table using.
+ * @cache:	MMU page cache to allocate new page tables from, or NULL.
+ *
+ * Walk the page tables pointed to by @pgd to find the PTE corresponding to the
+ * address @addr. If page tables don't exist for @addr, they will be created
+ * from the MMU cache if @cache is not NULL.
+ *
+ * Returns:	Pointer to pte_t corresponding to @addr.
+ *		NULL if a page table doesn't exist for @addr and !@...he.
+ *		NULL if a page table allocation failed.
+ */
+static pte_t *kvm_walk_pgd(pgd_t *pgd, struct kvm_mmu_memory_cache *cache,
+				unsigned long addr)
+{
+	p4d_t *p4d;
+	pud_t *pud;
+	pmd_t *pmd;
+
+	pgd += pgd_index(addr);
+	if (pgd_none(*pgd)) {
+		/* Not used yet */
+		BUG();
+		return NULL;
+	}
+	p4d = p4d_offset(pgd, addr);
+	pud = pud_offset(p4d, addr);
+	if (pud_none(*pud)) {
+		pmd_t *new_pmd;
+
+		if (!cache)
+			return NULL;
+		new_pmd = kvm_mmu_memory_cache_alloc(cache);
+		pmd_init((void *)new_pmd);
+		pud_populate(NULL, pud, new_pmd);
+	}
+	pmd = pmd_offset(pud, addr);
+	if (pmd_none(*pmd)) {
+		pte_t *new_pte;
+
+		if (!cache)
+			return NULL;
+		new_pte = kvm_mmu_memory_cache_alloc(cache);
+		clear_page(new_pte);
+		pmd_populate_kernel(NULL, pmd, new_pte);
+	}
+	return pte_offset_kernel(pmd, addr);
+}
+
+/* Caller must hold kvm->mm_lock */
+static pte_t *kvm_pte_for_gpa(struct kvm *kvm,
+				struct kvm_mmu_memory_cache *cache,
+				unsigned long addr)
+{
+	return kvm_walk_pgd(kvm->arch.gpa_mm.pgd, cache, addr);
+}
+
+/*
+ * kvm_flush_gpa_{pte,pmd,pud,pgd,pt}.
+ * Flush a range of guest physical address space from the VM's GPA page tables.
+ */
+
+static bool kvm_flush_gpa_pte(pte_t *pte, unsigned long start_gpa,
+				   unsigned long end_gpa, unsigned long *data)
+{
+	int i_min = pte_index(start_gpa);
+	int i_max = pte_index(end_gpa);
+	bool safe_to_remove = (i_min == 0 && i_max == PTRS_PER_PTE - 1);
+	int i;
+
+	for (i = i_min; i <= i_max; ++i) {
+		if (!pte_present(pte[i]))
+			continue;
+
+		set_pte(pte + i, __pte(0));
+		if (data)
+			*data += 1;
+	}
+	return safe_to_remove;
+}
+
+static bool kvm_flush_gpa_pmd(pmd_t *pmd, unsigned long start_gpa,
+				   unsigned long end_gpa, unsigned long *data)
+{
+	pte_t *pte;
+	unsigned long end = ~0ul;
+	int i_min = pmd_index(start_gpa);
+	int i_max = pmd_index(end_gpa);
+	bool safe_to_remove = (i_min == 0 && i_max == PTRS_PER_PMD - 1);
+	int i;
+
+	for (i = i_min; i <= i_max; ++i, start_gpa = 0) {
+		if (!pmd_present(pmd[i]))
+			continue;
+
+		pte = pte_offset_kernel(pmd + i, 0);
+		if (i == i_max)
+			end = end_gpa;
+
+		if (kvm_flush_gpa_pte(pte, start_gpa, end, data)) {
+			pmd_clear(pmd + i);
+			pte_free_kernel(NULL, pte);
+		} else {
+			safe_to_remove = false;
+		}
+	}
+	return safe_to_remove;
+}
+
+static bool kvm_flush_gpa_pud(pud_t *pud, unsigned long start_gpa,
+				   unsigned long end_gpa, unsigned long *data)
+{
+	pmd_t *pmd;
+	unsigned long end = ~0ul;
+	int i_min = pud_index(start_gpa);
+	int i_max = pud_index(end_gpa);
+	bool safe_to_remove = (i_min == 0 && i_max == PTRS_PER_PUD - 1);
+	int i;
+
+	for (i = i_min; i <= i_max; ++i, start_gpa = 0) {
+		if (!pud_present(pud[i]))
+			continue;
+
+		pmd = pmd_offset(pud + i, 0);
+		if (i == i_max)
+			end = end_gpa;
+
+		if (kvm_flush_gpa_pmd(pmd, start_gpa, end, data)) {
+			pud_clear(pud + i);
+			pmd_free(NULL, pmd);
+		} else {
+			safe_to_remove = false;
+		}
+	}
+	return safe_to_remove;
+}
+
+static bool kvm_flush_gpa_pgd(pgd_t *pgd, unsigned long start_gpa,
+				unsigned long end_gpa, unsigned long *data)
+{
+	p4d_t *p4d;
+	pud_t *pud;
+	unsigned long end = ~0ul;
+	int i_min = pgd_index(start_gpa);
+	int i_max = pgd_index(end_gpa);
+	bool safe_to_remove = (i_min == 0 && i_max == PTRS_PER_PGD - 1);
+	int i;
+
+	for (i = i_min; i <= i_max; ++i, start_gpa = 0) {
+		if (!pgd_present(pgd[i]))
+			continue;
+
+		p4d = p4d_offset(pgd, 0);
+		pud = pud_offset(p4d + i, 0);
+		if (i == i_max)
+			end = end_gpa;
+
+		if (kvm_flush_gpa_pud(pud, start_gpa, end, data)) {
+			pgd_clear(pgd + i);
+			pud_free(NULL, pud);
+		} else {
+			safe_to_remove = false;
+		}
+	}
+	return safe_to_remove;
+}
+
+/**
+ * kvm_flush_gpa_range() - Flush a range of guest physical addresses.
+ * @kvm:	KVM pointer.
+ * @start_gfn:	Guest frame number of first page in GPA range to flush.
+ * @end_gfn:	Guest frame number of last page in GPA range to flush.
+ *
+ * Flushes a range of GPA mappings from the GPA page tables.
+ *
+ * The caller must hold the @kvm->mmu_lock spinlock.
+ *
+ * Returns:	Whether its safe to remove the top level page directory because
+ *		all lower levels have been removed.
+ */
+static bool kvm_flush_gpa_range(struct kvm *kvm, gfn_t start_gfn, gfn_t end_gfn, void *data)
+{
+	return kvm_flush_gpa_pgd(kvm->arch.gpa_mm.pgd,
+				start_gfn << PAGE_SHIFT,
+				end_gfn << PAGE_SHIFT, (unsigned long *)data);
+}
+
+/*
+ * kvm_mkclean_gpa_pt.
+ * Mark a range of guest physical address space clean (writes fault) in the VM's
+ * GPA page table to allow dirty page tracking.
+ */
+
+static int kvm_mkclean_pte(pte_t *pte, unsigned long start, unsigned long end)
+{
+	int ret = 0;
+	int i_min = pte_index(start);
+	int i_max = pte_index(end);
+	int i;
+	pte_t val;
+
+	for (i = i_min; i <= i_max; ++i) {
+		val = pte[i];
+		if (pte_present(val) && pte_dirty(val)) {
+			set_pte(pte + i, pte_mkclean(val));
+			ret = 1;
+		}
+	}
+	return ret;
+}
+
+static int kvm_mkclean_pmd(pmd_t *pmd, unsigned long start, unsigned long end)
+{
+	int ret = 0;
+	pte_t *pte;
+	unsigned long cur_end = ~0ul;
+	int i_min = pmd_index(start);
+	int i_max = pmd_index(end);
+	int i;
+
+	for (i = i_min; i <= i_max; ++i, start = 0) {
+		if (!pmd_present(pmd[i]))
+			continue;
+
+		pte = pte_offset_kernel(pmd + i, 0);
+		if (i == i_max)
+			cur_end = end;
+
+		ret |= kvm_mkclean_pte(pte, start, cur_end);
+	}
+
+	return ret;
+}
+
+static int kvm_mkclean_pud(pud_t *pud, unsigned long start, unsigned long end)
+{
+	int ret = 0;
+	pmd_t *pmd;
+	unsigned long cur_end = ~0ul;
+	int i_min = pud_index(start);
+	int i_max = pud_index(end);
+	int i;
+
+	for (i = i_min; i <= i_max; ++i, start = 0) {
+		if (!pud_present(pud[i]))
+			continue;
+
+		pmd = pmd_offset(pud + i, 0);
+		if (i == i_max)
+			cur_end = end;
+
+		ret |= kvm_mkclean_pmd(pmd, start, cur_end);
+	}
+	return ret;
+}
+
+static int kvm_mkclean_pgd(pgd_t *pgd, unsigned long start, unsigned long end)
+{
+	int ret = 0;
+	p4d_t *p4d;
+	pud_t *pud;
+	unsigned long cur_end = ~0ul;
+	int i_min = pgd_index(start);
+	int i_max = pgd_index(end);
+	int i;
+
+	for (i = i_min; i <= i_max; ++i, start = 0) {
+		if (!pgd_present(pgd[i]))
+			continue;
+
+		p4d = p4d_offset(pgd, 0);
+		pud = pud_offset(p4d + i, 0);
+		if (i == i_max)
+			cur_end = end;
+
+		ret |= kvm_mkclean_pud(pud, start, cur_end);
+	}
+	return ret;
+}
+
+/**
+ * kvm_mkclean_gpa_pt() - Make a range of guest physical addresses clean.
+ * @kvm:	KVM pointer.
+ * @start_gfn:	Guest frame number of first page in GPA range to flush.
+ * @end_gfn:	Guest frame number of last page in GPA range to flush.
+ *
+ * Make a range of GPA mappings clean so that guest writes will fault and
+ * trigger dirty page logging.
+ *
+ * The caller must hold the @kvm->mmu_lock spinlock.
+ *
+ * Returns:	Whether any GPA mappings were modified, which would require
+ *		derived mappings (GVA page tables & TLB enties) to be
+ *		invalidated.
+ */
+static int kvm_mkclean_gpa_pt(struct kvm *kvm, gfn_t start_gfn, gfn_t end_gfn)
+{
+	return kvm_mkclean_pgd(kvm->arch.gpa_mm.pgd, start_gfn << PAGE_SHIFT,
+				end_gfn << PAGE_SHIFT);
+}
+
+/**
+ * kvm_arch_mmu_enable_log_dirty_pt_masked() - write protect dirty pages
+ * @kvm:	The KVM pointer
+ * @slot:	The memory slot associated with mask
+ * @gfn_offset:	The gfn offset in memory slot
+ * @mask:	The mask of dirty pages at offset 'gfn_offset' in this memory
+ *		slot to be write protected
+ *
+ * Walks bits set in mask write protects the associated pte's. Caller must
+ * acquire @kvm->mmu_lock.
+ */
+void kvm_arch_mmu_enable_log_dirty_pt_masked(struct kvm *kvm,
+		struct kvm_memory_slot *slot,
+		gfn_t gfn_offset, unsigned long mask)
+{
+	gfn_t base_gfn = slot->base_gfn + gfn_offset;
+	gfn_t start = base_gfn +  __ffs(mask);
+	gfn_t end = base_gfn + __fls(mask);
+
+	kvm_mkclean_gpa_pt(kvm, start, end);
+}
+
+void kvm_arch_commit_memory_region(struct kvm *kvm,
+				   struct kvm_memory_slot *old,
+				   const struct kvm_memory_slot *new,
+				   enum kvm_mr_change change)
+{
+	int needs_flush;
+
+	/*
+	 * If dirty page logging is enabled, write protect all pages in the slot
+	 * ready for dirty logging.
+	 *
+	 * There is no need to do this in any of the following cases:
+	 * CREATE:	No dirty mappings will already exist.
+	 * MOVE/DELETE:	The old mappings will already have been cleaned up by
+	 *		kvm_arch_flush_shadow_memslot()
+	 */
+	if (change == KVM_MR_FLAGS_ONLY &&
+	    (!(old->flags & KVM_MEM_LOG_DIRTY_PAGES) &&
+	     new->flags & KVM_MEM_LOG_DIRTY_PAGES)) {
+		spin_lock(&kvm->mmu_lock);
+		/* Write protect GPA page table entries */
+		needs_flush = kvm_mkclean_gpa_pt(kvm, new->base_gfn,
+					new->base_gfn + new->npages - 1);
+		if (needs_flush)
+			kvm_flush_remote_tlbs(kvm);
+		spin_unlock(&kvm->mmu_lock);
+	}
+}
+
+void kvm_arch_flush_shadow_all(struct kvm *kvm)
+{
+	/* Flush whole GPA */
+	kvm_flush_gpa_range(kvm, 0, ~0UL, NULL);
+	/* Flush vpid for each VCPU individually */
+	kvm_flush_remote_tlbs(kvm);
+}
+
+void kvm_arch_flush_shadow_memslot(struct kvm *kvm,
+		struct kvm_memory_slot *slot)
+{
+	unsigned long npages;
+
+	/*
+	 * The slot has been made invalid (ready for moving or deletion), so we
+	 * need to ensure that it can no longer be accessed by any guest VCPUs.
+	 */
+
+	npages = 0;
+	spin_lock(&kvm->mmu_lock);
+	/* Flush slot from GPA */
+	kvm_flush_gpa_range(kvm, slot->base_gfn,
+			slot->base_gfn + slot->npages - 1, &npages);
+	/* Let implementation do the rest */
+	if (npages)
+		kvm_flush_remote_tlbs(kvm);
+	spin_unlock(&kvm->mmu_lock);
+}
+
+void _kvm_destroy_mm(struct kvm *kvm)
+{
+	/* It should always be safe to remove after flushing the whole range */
+	WARN_ON(!kvm_flush_gpa_range(kvm, 0, ~0UL, NULL));
+	pgd_free(NULL, kvm->arch.gpa_mm.pgd);
+	kvm->arch.gpa_mm.pgd = NULL;
+}
+
+/*
+ * Mark a range of guest physical address space old (all accesses fault) in the
+ * VM's GPA page table to allow detection of commonly used pages.
+ */
+
+static int kvm_mkold_pte(pte_t *pte, unsigned long start, unsigned long end)
+{
+	int ret = 0;
+	int i_min = pte_index(start);
+	int i_max = pte_index(end);
+	int i;
+	pte_t old, new;
+
+	for (i = i_min; i <= i_max; ++i) {
+		if (!pte_present(pte[i]))
+			continue;
+
+		old = pte[i];
+		new = pte_mkold(old);
+		if (pte_val(new) == pte_val(old))
+			continue;
+		set_pte(pte + i, new);
+		ret = 1;
+	}
+
+	return ret;
+}
+
+static int kvm_mkold_pmd(pmd_t *pmd, unsigned long start, unsigned long end)
+{
+	int ret = 0;
+	pte_t *pte;
+	unsigned long cur_end = ~0ul;
+	int i_min = pmd_index(start);
+	int i_max = pmd_index(end);
+	int i;
+
+	for (i = i_min; i <= i_max; ++i, start = 0) {
+		if (!pmd_present(pmd[i]))
+			continue;
+
+		pte = pte_offset_kernel(pmd + i, 0);
+		if (i == i_max)
+			cur_end = end;
+
+		ret |= kvm_mkold_pte(pte, start, cur_end);
+	}
+
+	return ret;
+}
+
+static int kvm_mkold_pud(pud_t *pud, unsigned long start, unsigned long end)
+{
+	int ret = 0;
+	pmd_t *pmd;
+	unsigned long cur_end = ~0ul;
+	int i_min = pud_index(start);
+	int i_max = pud_index(end);
+	int i;
+
+	for (i = i_min; i <= i_max; ++i, start = 0) {
+		if (!pud_present(pud[i]))
+			continue;
+
+		pmd = pmd_offset(pud + i, 0);
+		if (i == i_max)
+			cur_end = end;
+
+		ret |= kvm_mkold_pmd(pmd, start, cur_end);
+	}
+
+	return ret;
+}
+
+static int kvm_mkold_pgd(pgd_t *pgd, unsigned long start, unsigned long end)
+{
+	int ret = 0;
+	p4d_t *p4d;
+	pud_t *pud;
+	unsigned long cur_end = ~0ul;
+	int i_min = pgd_index(start);
+	int i_max = pgd_index(end);
+	int i;
+
+	for (i = i_min; i <= i_max; ++i, start = 0) {
+		if (!pgd_present(pgd[i]))
+			continue;
+
+		p4d = p4d_offset(pgd, 0);
+		pud = pud_offset(p4d + i, 0);
+		if (i == i_max)
+			cur_end = end;
+
+		ret |= kvm_mkold_pud(pud, start, cur_end);
+	}
+
+	return ret;
+}
+
+bool kvm_unmap_gfn_range(struct kvm *kvm, struct kvm_gfn_range *range)
+{
+	unsigned long npages = 0;
+
+	kvm_flush_gpa_range(kvm, range->start, range->end, &npages);
+	return npages > 0;
+}
+
+bool kvm_set_spte_gfn(struct kvm *kvm, struct kvm_gfn_range *range)
+{
+	gpa_t gpa = range->start << PAGE_SHIFT;
+	pte_t hva_pte = range->pte;
+	pte_t *ptep = kvm_pte_for_gpa(kvm, NULL, gpa);
+	pte_t old_pte;
+
+	if (!ptep)
+		return false;
+
+	/* Mapping may need adjusting depending on memslot flags */
+	old_pte = *ptep;
+	if (range->slot->flags & KVM_MEM_LOG_DIRTY_PAGES && !pte_dirty(old_pte))
+		hva_pte = pte_mkclean(hva_pte);
+	else if (range->slot->flags & KVM_MEM_READONLY)
+		hva_pte = pte_wrprotect(hva_pte);
+
+	set_pte(ptep, hva_pte);
+
+	/* Replacing an absent or old page doesn't need flushes */
+	if (!pte_present(old_pte) || !pte_young(old_pte))
+		return false;
+
+	/* Pages swapped, aged, moved, or cleaned require flushes */
+	return !pte_present(hva_pte) ||
+	       !pte_young(hva_pte) ||
+	       pte_pfn(old_pte) != pte_pfn(hva_pte) ||
+	       (pte_dirty(old_pte) && !pte_dirty(hva_pte));
+}
+
+bool kvm_age_gfn(struct kvm *kvm, struct kvm_gfn_range *range)
+{
+	return kvm_mkold_pgd(kvm->arch.gpa_mm.pgd, range->start << PAGE_SHIFT,
+				range->end << PAGE_SHIFT);
+}
+
+bool kvm_test_age_gfn(struct kvm *kvm, struct kvm_gfn_range *range)
+{
+	gpa_t gpa = range->start << PAGE_SHIFT;
+	pte_t *ptep = kvm_pte_for_gpa(kvm, NULL, gpa);
+
+	if (ptep && pte_present(*ptep) && pte_young(*ptep))
+		return true;
+
+	return false;
+}
+
+/**
+ * kvm_map_page_fast() - Fast path GPA fault handler.
+ * @vcpu:		VCPU pointer.
+ * @gpa:		Guest physical address of fault.
+ * @write:	Whether the fault was due to a write.
+ *
+ * Perform fast path GPA fault handling, doing all that can be done without
+ * calling into KVM. This handles marking old pages young (for idle page
+ * tracking), and dirtying of clean pages (for dirty page logging).
+ *
+ * Returns:	0 on success, in which case we can update derived mappings and
+ *		resume guest execution.
+ *		-EFAULT on failure due to absent GPA mapping or write to
+ *		read-only page, in which case KVM must be consulted.
+ */
+static int kvm_map_page_fast(struct kvm_vcpu *vcpu, unsigned long gpa,
+				   bool write)
+{
+	struct kvm *kvm = vcpu->kvm;
+	gfn_t gfn = gpa >> PAGE_SHIFT;
+	pte_t *ptep;
+	kvm_pfn_t pfn = 0;
+	bool pfn_valid = false;
+	int ret = 0;
+
+	spin_lock(&kvm->mmu_lock);
+
+	/* Fast path - just check GPA page table for an existing entry */
+	ptep = kvm_pte_for_gpa(kvm, NULL, gpa);
+	if (!ptep || !pte_present(*ptep)) {
+		ret = -EFAULT;
+		goto out;
+	}
+
+	/* Track access to pages marked old */
+	if (!pte_young(*ptep)) {
+		set_pte(ptep, pte_mkyoung(*ptep));
+		pfn = pte_pfn(*ptep);
+		pfn_valid = true;
+		/* call kvm_set_pfn_accessed() after unlock */
+	}
+	if (write && !pte_dirty(*ptep)) {
+		if (!pte_write(*ptep)) {
+			ret = -EFAULT;
+			goto out;
+		}
+
+		/* Track dirtying of writeable pages */
+		set_pte(ptep, pte_mkdirty(*ptep));
+		pfn = pte_pfn(*ptep);
+		mark_page_dirty(kvm, gfn);
+		kvm_set_pfn_dirty(pfn);
+	}
+
+out:
+	spin_unlock(&kvm->mmu_lock);
+	if (pfn_valid)
+		kvm_set_pfn_accessed(pfn);
+	return ret;
+}
+
+/**
+ * kvm_map_page() - Map a guest physical page.
+ * @vcpu:		VCPU pointer.
+ * @gpa:		Guest physical address of fault.
+ * @write:	Whether the fault was due to a write.
+ *
+ * Handle GPA faults by creating a new GPA mapping (or updating an existing
+ * one).
+ *
+ * This takes care of marking pages young or dirty (idle/dirty page tracking),
+ * asking KVM for the corresponding PFN, and creating a mapping in the GPA page
+ * tables. Derived mappings (GVA page tables and TLBs) must be handled by the
+ * caller.
+ *
+ * Returns:	0 on success
+ *		-EFAULT if there is no memory region at @gpa or a write was
+ *		attempted to a read-only memory region. This is usually handled
+ *		as an MMIO access.
+ */
+static int kvm_map_page(struct kvm_vcpu *vcpu, unsigned long gpa, bool write)
+{
+	bool writeable;
+	int srcu_idx, err = 0, retry_no = 0;
+	unsigned long hva;
+	unsigned long mmu_seq;
+	unsigned long prot_bits;
+	pte_t *ptep, new_pte;
+	kvm_pfn_t pfn;
+	gfn_t gfn = gpa >> PAGE_SHIFT;
+	struct vm_area_struct *vma;
+	struct kvm *kvm = vcpu->kvm;
+	struct kvm_memory_slot *memslot;
+	struct kvm_mmu_memory_cache *memcache = &vcpu->arch.mmu_page_cache;
+
+	/* Try the fast path to handle old / clean pages */
+	srcu_idx = srcu_read_lock(&kvm->srcu);
+	err = kvm_map_page_fast(vcpu, gpa, write);
+	if (!err)
+		goto out;
+
+	memslot = gfn_to_memslot(kvm, gfn);
+	hva = gfn_to_hva_memslot_prot(memslot, gfn, &writeable);
+	if (kvm_is_error_hva(hva) || (write && !writeable))
+		goto out;
+
+	/* Let's check if we will get back a huge page backed by hugetlbfs */
+	mmap_read_lock(current->mm);
+	vma = find_vma_intersection(current->mm, hva, hva + 1);
+	if (unlikely(!vma)) {
+		kvm_err("Failed to find VMA for hva 0x%lx\n", hva);
+		mmap_read_unlock(current->mm);
+		err = -EFAULT;
+		goto out;
+	}
+	mmap_read_unlock(current->mm);
+
+	/* We need a minimum of cached pages ready for page table creation */
+	err = kvm_mmu_topup_memory_cache(memcache, KVM_MMU_CACHE_MIN_PAGES);
+	if (err)
+		goto out;
+
+retry:
+	/*
+	 * Used to check for invalidations in progress, of the pfn that is
+	 * returned by pfn_to_pfn_prot below.
+	 */
+	mmu_seq = kvm->mmu_invalidate_seq;
+	/*
+	 * Ensure the read of mmu_invalidate_seq isn't reordered with PTE reads in
+	 * gfn_to_pfn_prot() (which calls get_user_pages()), so that we don't
+	 * risk the page we get a reference to getting unmapped before we have a
+	 * chance to grab the mmu_lock without mmu_invalidate_retry() noticing.
+	 *
+	 * This smp_rmb() pairs with the effective smp_wmb() of the combination
+	 * of the pte_unmap_unlock() after the PTE is zapped, and the
+	 * spin_lock() in kvm_mmu_invalidate_invalidate_<page|range_end>() before
+	 * mmu_invalidate_seq is incremented.
+	 */
+	smp_rmb();
+
+	/* Slow path - ask KVM core whether we can access this GPA */
+	pfn = gfn_to_pfn_prot(kvm, gfn, write, &writeable);
+	if (is_error_noslot_pfn(pfn)) {
+		err = -EFAULT;
+		goto out;
+	}
+
+	spin_lock(&kvm->mmu_lock);
+	/* Check if an invalidation has taken place since we got pfn */
+	if (mmu_invalidate_retry(kvm, mmu_seq)) {
+		/*
+		 * This can happen when mappings are changed asynchronously, but
+		 * also synchronously if a COW is triggered by
+		 * gfn_to_pfn_prot().
+		 */
+		spin_unlock(&kvm->mmu_lock);
+		kvm_set_pfn_accessed(pfn);
+		kvm_release_pfn_clean(pfn);
+		if (retry_no > 100) {
+			retry_no = 0;
+			schedule();
+		}
+		retry_no++;
+		goto retry;
+	}
+
+	/*
+	 * For emulated devices such virtio device, actual cache attribute is
+	 * determined by physical machine.
+	 * For pass through physical device, it should be uncachable
+	 */
+	prot_bits = _PAGE_PRESENT | __READABLE;
+	if (vma->vm_flags & (VM_IO | VM_PFNMAP))
+		prot_bits |= _CACHE_SUC;
+	else
+		prot_bits |= _CACHE_CC;
+
+	if (writeable) {
+		prot_bits |= _PAGE_WRITE;
+		if (write) {
+			prot_bits |= __WRITEABLE;
+			mark_page_dirty(kvm, gfn);
+			kvm_set_pfn_dirty(pfn);
+		}
+	}
+
+	/* Ensure page tables are allocated */
+	ptep = kvm_pte_for_gpa(kvm, memcache, gpa);
+	new_pte = pfn_pte(pfn, __pgprot(prot_bits));
+	set_pte(ptep, new_pte);
+
+	err = 0;
+	spin_unlock(&kvm->mmu_lock);
+	kvm_release_pfn_clean(pfn);
+	kvm_set_pfn_accessed(pfn);
+out:
+	srcu_read_unlock(&kvm->srcu, srcu_idx);
+	return err;
+}
+
+int kvm_handle_mm_fault(struct kvm_vcpu *vcpu, unsigned long gpa, bool write)
+{
+	int ret;
+
+	ret = kvm_map_page(vcpu, gpa, write);
+	if (ret)
+		return ret;
+
+	/* Invalidate this entry in the TLB */
+	return kvm_flush_tlb_gpa(vcpu, gpa);
+}
+
+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)
+{
+	kvm_flush_remote_tlbs(kvm);
+}
-- 
2.31.1

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