Message-ID: <32d56f21-d18e-56a9-3dc2-01555f90c949@loongson.cn>
Date:   Mon, 13 Mar 2023 09:31:20 +0800
From:   Tianrui Zhao <zhaotianrui@...ngson.cn>
To:     maobibo <maobibo@...ngson.cn>, 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>,
        Oliver Upton <oliver.upton@...ux.dev>,
        Xi Ruoyao <xry111@...111.site>
Subject: Re: [PATCH v3 19/29] LoongArch: KVM: Implement kvm mmu operations




在 2023年03月07日 10:49, maobibo 写道:
>
> 在 2023/2/28 15:00, Tianrui Zhao 写道:
>> 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 000000000000..049824f8e462
>> --- /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));
> Only _kvm_destroy_mm cares about return value about function
> kvm_flush_gpa_range, it always return true since it is flushing
> the whole range.
>
> Can return value of function kvm_flush_gpa_range be defined as void rather
> than bool?  By this way, safe_to_remove can be removed in function kvm_flush_gpa_pgd
> etc.
>
> Regards
> Bibo, Mao
>
Thanks, It is more suitable to use void return value in 
kvm_flush_gpa_range, and the safe_to_remove flag can be removed as it 
has no effect in the function.

Thank
Tianrui Zhao
>> +	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);
>> +}

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