mips/kvm/mmu.c

/*
 * This file is subject to the terms and conditions of the GNU General Public
 * License.  See the file "COPYING" in the main directory of this archive
 * for more details.
 *
 * KVM/MIPS MMU handling in the KVM module.
 *
 * Copyright (C) 2012  MIPS Technologies, Inc.  All rights reserved.
 * Authors: Sanjay Lal <sanjayl@kymasys.com>
 */

#include <linux/highmem.h>
#include <linux/kvm_host.h>
#include <linux/uaccess.h>
#include <asm/mmu_context.h>
#include <asm/pgalloc.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

void kvm_mmu_free_memory_caches(struct kvm_vcpu *vcpu)
{
	kvm_mmu_free_memory_cache(&vcpu->arch.mmu_page_cache);
}

/**
 * kvm_pgd_init() - Initialise KVM GPA page directory.
 * @page:	Pointer to page directory (PGD) for KVM GPA.
 *
 * Initialise a KVM GPA page directory with pointers to the invalid table, i.e.
 * representing no mappings. This is similar to pgd_init(), however it
 * initialises all the page directory pointers, not just the ones corresponding
 * to the userland address space (since it is for the guest physical address
 * space rather than a virtual address space).
 */
static void kvm_pgd_init(void *page)
{
	unsigned long *p, *end;
	unsigned long entry;

#ifdef __PAGETABLE_PMD_FOLDED
	entry = (unsigned long)invalid_pte_table;
#else
	entry = (unsigned long)invalid_pmd_table;
#endif

	p = (unsigned long *)page;
	end = p + PTRS_PER_PGD;

	do {
		p[0] = entry;
		p[1] = entry;
		p[2] = entry;
		p[3] = entry;
		p[4] = entry;
		p += 8;
		p[-3] = entry;
		p[-2] = entry;
		p[-1] = entry;
	} while (p != end);
}

/**
 * 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 *ret;

	ret = (pgd_t *)__get_free_pages(GFP_KERNEL, PGD_TABLE_ORDER);
	if (ret)
		kvm_pgd_init(ret);

	return ret;
}

/**
 * kvm_mips_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 !@cache.
 *		NULL if a page table allocation failed.
 */
static pte_t *kvm_mips_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 on MIPS 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(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_mips_pte_for_gpa(struct kvm *kvm,
				   struct kvm_mmu_memory_cache *cache,
				   unsigned long addr)
{
	return kvm_mips_walk_pgd(kvm->arch.gpa_mm.pgd, cache, addr);
}

/*
 * kvm_mips_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_mips_flush_gpa_pte(pte_t *pte, unsigned long start_gpa,
				   unsigned long end_gpa)
{
	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));
	}
	return safe_to_remove;
}

static bool kvm_mips_flush_gpa_pmd(pmd_t *pmd, unsigned long start_gpa,
				   unsigned long end_gpa)
{
	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_mips_flush_gpa_pte(pte, start_gpa, end)) {
			pmd_clear(pmd + i);
			pte_free_kernel(NULL, pte);
		} else {
			safe_to_remove = false;
		}
	}
	return safe_to_remove;
}

static bool kvm_mips_flush_gpa_pud(pud_t *pud, unsigned long start_gpa,
				   unsigned long end_gpa)
{
	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_mips_flush_gpa_pmd(pmd, start_gpa, end)) {
			pud_clear(pud + i);
			pmd_free(NULL, pmd);
		} else {
			safe_to_remove = false;
		}
	}
	return safe_to_remove;
}

static bool kvm_mips_flush_gpa_pgd(pgd_t *pgd, unsigned long start_gpa,
				   unsigned long end_gpa)
{
	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_mips_flush_gpa_pud(pud, start_gpa, end)) {
			pgd_clear(pgd + i);
			pud_free(NULL, pud);
		} else {
			safe_to_remove = false;
		}
	}
	return safe_to_remove;
}

/**
 * kvm_mips_flush_gpa_pt() - 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.
 */
bool kvm_mips_flush_gpa_pt(struct kvm *kvm, gfn_t start_gfn, gfn_t end_gfn)
{
	return kvm_mips_flush_gpa_pgd(kvm->arch.gpa_mm.pgd,
				      start_gfn << PAGE_SHIFT,
				      end_gfn << PAGE_SHIFT);
}

#define BUILD_PTE_RANGE_OP(name, op)					\
static int kvm_mips_##name##_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 = op(old);						\
		if (pte_val(new) == pte_val(old))			\
			continue;					\
		set_pte(pte + i, new);					\
		ret = 1;						\
	}								\
	return ret;							\
}									\
									\
/* returns true if anything was done */					\
static int kvm_mips_##name##_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_mips_##name##_pte(pte, start, cur_end);	\
	}								\
	return ret;							\
}									\
									\
static int kvm_mips_##name##_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_mips_##name##_pmd(pmd, start, cur_end);	\
	}								\
	return ret;							\
}									\
									\
static int kvm_mips_##name##_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_mips_##name##_pud(pud, start, cur_end);	\
	}								\
	return ret;							\
}

/*
 * kvm_mips_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.
 */

BUILD_PTE_RANGE_OP(mkclean, pte_mkclean)

/**
 * kvm_mips_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.
 */
int kvm_mips_mkclean_gpa_pt(struct kvm *kvm, gfn_t start_gfn, gfn_t end_gfn)
{
	return kvm_mips_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_mips_mkclean_gpa_pt(kvm, start, end);
}

/*
 * kvm_mips_mkold_gpa_pt.
 * 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.
 */

BUILD_PTE_RANGE_OP(mkold, pte_mkold)

static int kvm_mips_mkold_gpa_pt(struct kvm *kvm, gfn_t start_gfn,
				 gfn_t end_gfn)
{
	return kvm_mips_mkold_pgd(kvm->arch.gpa_mm.pgd,
				  start_gfn << PAGE_SHIFT,
				  end_gfn << PAGE_SHIFT);
}

bool kvm_unmap_gfn_range(struct kvm *kvm, struct kvm_gfn_range *range)
{
	kvm_mips_flush_gpa_pt(kvm, range->start, range->end);
	return true;
}

bool kvm_age_gfn(struct kvm *kvm, struct kvm_gfn_range *range)
{
	return kvm_mips_mkold_gpa_pt(kvm, range->start, range->end);
}

bool kvm_test_age_gfn(struct kvm *kvm, struct kvm_gfn_range *range)
{
	gpa_t gpa = range->start << PAGE_SHIFT;
	pte_t *gpa_pte = kvm_mips_pte_for_gpa(kvm, NULL, gpa);

	if (!gpa_pte)
		return false;
	return pte_young(*gpa_pte);
}

/**
 * _kvm_mips_map_page_fast() - Fast path GPA fault handler.
 * @vcpu:		VCPU pointer.
 * @gpa:		Guest physical address of fault.
 * @write_fault:	Whether the fault was due to a write.
 * @out_entry:		New PTE for @gpa (written on success unless NULL).
 * @out_buddy:		New PTE for @gpa's buddy (written on success unless
 *			NULL).
 *
 * 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_mips_map_page_fast(struct kvm_vcpu *vcpu, unsigned long gpa,
				   bool write_fault,
				   pte_t *out_entry, pte_t *out_buddy)
{
	struct kvm *kvm = vcpu->kvm;
	gfn_t gfn = gpa >> PAGE_SHIFT;
	pte_t *ptep;
	int ret = 0;

	spin_lock(&kvm->mmu_lock);

	/* Fast path - just check GPA page table for an existing entry */
	ptep = kvm_mips_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));

	if (write_fault && !pte_dirty(*ptep)) {
		if (!pte_write(*ptep)) {
			ret = -EFAULT;
			goto out;
		}

		/* Track dirtying of writeable pages */
		set_pte(ptep, pte_mkdirty(*ptep));
		mark_page_dirty(kvm, gfn);
	}

	if (out_entry)
		*out_entry = *ptep;
	if (out_buddy)
		*out_buddy = *ptep_buddy(ptep);

out:
	spin_unlock(&kvm->mmu_lock);
	return ret;
}

/**
 * kvm_mips_map_page() - Map a guest physical page.
 * @vcpu:		VCPU pointer.
 * @gpa:		Guest physical address of fault.
 * @write_fault:	Whether the fault was due to a write.
 * @out_entry:		New PTE for @gpa (written on success unless NULL).
 * @out_buddy:		New PTE for @gpa's buddy (written on success unless
 *			NULL).
 *
 * 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, in which case the caller may use the @out_entry
 *		and @out_buddy PTEs to update derived mappings and resume guest
 *		execution.
 *		-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_mips_map_page(struct kvm_vcpu *vcpu, unsigned long gpa,
			     bool write_fault,
			     pte_t *out_entry, pte_t *out_buddy)
{
	struct kvm *kvm = vcpu->kvm;
	struct kvm_mmu_memory_cache *memcache = &vcpu->arch.mmu_page_cache;
	gfn_t gfn = gpa >> PAGE_SHIFT;
	int srcu_idx, err;
	kvm_pfn_t pfn;
	pte_t *ptep, entry;
	bool writeable;
	unsigned long prot_bits;
	unsigned long mmu_seq;
	struct page *page;

	/* Try the fast path to handle old / clean pages */
	srcu_idx = srcu_read_lock(&kvm->srcu);
	err = _kvm_mips_map_page_fast(vcpu, gpa, write_fault, out_entry,
				      out_buddy);
	if (!err)
		goto out;

	/* 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 kvm_faultin_pfn() (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_notifier_invalidate_<page|range_end>() before
	 * mmu_invalidate_seq is incremented.
	 */
	smp_rmb();

	/* Slow path - ask KVM core whether we can access this GPA */
	pfn = kvm_faultin_pfn(vcpu, gfn, write_fault, &writeable, &page);
	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
		 * kvm_faultin_pfn().
		 */
		spin_unlock(&kvm->mmu_lock);
		kvm_release_page_unused(page);
		goto retry;
	}

	/* Ensure page tables are allocated */
	ptep = kvm_mips_pte_for_gpa(kvm, memcache, gpa);

	/* Set up the PTE */
	prot_bits = _PAGE_PRESENT | __READABLE | _page_cachable_default;
	if (writeable) {
		prot_bits |= _PAGE_WRITE;
		if (write_fault) {
			prot_bits |= __WRITEABLE;
			mark_page_dirty(kvm, gfn);
		}
	}
	entry = pfn_pte(pfn, __pgprot(prot_bits));

	/* Write the PTE */
	set_pte(ptep, entry);

	err = 0;
	if (out_entry)
		*out_entry = *ptep;
	if (out_buddy)
		*out_buddy = *ptep_buddy(ptep);

	kvm_release_faultin_page(kvm, page, false, writeable);
	spin_unlock(&kvm->mmu_lock);
out:
	srcu_read_unlock(&kvm->srcu, srcu_idx);
	return err;
}

int kvm_mips_handle_vz_root_tlb_fault(unsigned long badvaddr,
				      struct kvm_vcpu *vcpu,
				      bool write_fault)
{
	int ret;

	ret = kvm_mips_map_page(vcpu, badvaddr, write_fault, NULL, NULL);
	if (ret)
		return ret;

	/* Invalidate this entry in the TLB */
	return kvm_vz_host_tlb_inv(vcpu, badvaddr);
}

/**
 * kvm_mips_migrate_count() - Migrate timer.
 * @vcpu:	Virtual CPU.
 *
 * Migrate CP0_Count hrtimer to the current CPU by cancelling and restarting it
 * if it was running prior to being cancelled.
 *
 * Must be called when the VCPU is migrated to a different CPU to ensure that
 * timer expiry during guest execution interrupts the guest and causes the
 * interrupt to be delivered in a timely manner.
 */
static void kvm_mips_migrate_count(struct kvm_vcpu *vcpu)
{
	if (hrtimer_cancel(&vcpu->arch.comparecount_timer))
		hrtimer_restart(&vcpu->arch.comparecount_timer);
}

/* Restore ASID once we are scheduled back after preemption */
void kvm_arch_vcpu_load(struct kvm_vcpu *vcpu, int cpu)
{
	unsigned long flags;

	kvm_debug("%s: vcpu %p, cpu: %d\n", __func__, vcpu, cpu);

	local_irq_save(flags);

	vcpu->cpu = cpu;
	if (vcpu->arch.last_sched_cpu != cpu) {
		kvm_debug("[%d->%d]KVM VCPU[%d] switch\n",
			  vcpu->arch.last_sched_cpu, cpu, vcpu->vcpu_id);
		/*
		 * Migrate the timer interrupt to the current CPU so that it
		 * always interrupts the guest and synchronously triggers a
		 * guest timer interrupt.
		 */
		kvm_mips_migrate_count(vcpu);
	}

	/* restore guest state to registers */
	kvm_mips_callbacks->vcpu_load(vcpu, cpu);

	local_irq_restore(flags);
}

/* ASID can change if another task is scheduled during preemption */
void kvm_arch_vcpu_put(struct kvm_vcpu *vcpu)
{
	unsigned long flags;
	int cpu;

	local_irq_save(flags);

	cpu = smp_processor_id();
	vcpu->arch.last_sched_cpu = cpu;
	vcpu->cpu = -1;

	/* save guest state in registers */
	kvm_mips_callbacks->vcpu_put(vcpu, cpu);

	local_irq_restore(flags);
}