paging_tmpl.h

/*
 * Kernel-based Virtual Machine driver for Linux
 *
 * This module enables machines with Intel VT-x extensions to run virtual
 * machines without emulation or binary translation.
 *
 * MMU support
 *
 * Copyright (C) 2006 Qumranet, Inc.
 *
 * Authors:
 *   Yaniv Kamay  <yaniv@qumranet.com>
 *   Avi Kivity   <avi@qumranet.com>
 *
 * This work is licensed under the terms of the GNU GPL, version 2.  See
 * the COPYING file in the top-level directory.
 *
 */

/*
 * We need the mmu code to access both 32-bit and 64-bit guest ptes,
 * so the code in this file is compiled twice, once per pte size.
 */

#if PTTYPE == 64
	#define pt_element_t u64
	#define guest_walker guest_walker64
	#define shadow_walker shadow_walker64
	#define FNAME(name) paging##64_##name
	#define PT_BASE_ADDR_MASK PT64_BASE_ADDR_MASK
	#define PT_DIR_BASE_ADDR_MASK PT64_DIR_BASE_ADDR_MASK
	#define PT_INDEX(addr, level) PT64_INDEX(addr, level)
	#define PT_LEVEL_MASK(level) PT64_LEVEL_MASK(level)
	#define PT_LEVEL_BITS PT64_LEVEL_BITS
	#ifdef CONFIG_X86_64
	#define PT_MAX_FULL_LEVELS 4
	#define CMPXCHG cmpxchg
	#else
	#define CMPXCHG cmpxchg64
	#define PT_MAX_FULL_LEVELS 2
	#endif
#elif PTTYPE == 32
	#define pt_element_t u32
	#define guest_walker guest_walker32
	#define shadow_walker shadow_walker32
	#define FNAME(name) paging##32_##name
	#define PT_BASE_ADDR_MASK PT32_BASE_ADDR_MASK
	#define PT_DIR_BASE_ADDR_MASK PT32_DIR_BASE_ADDR_MASK
	#define PT_INDEX(addr, level) PT32_INDEX(addr, level)
	#define PT_LEVEL_MASK(level) PT32_LEVEL_MASK(level)
	#define PT_LEVEL_BITS PT32_LEVEL_BITS
	#define PT_MAX_FULL_LEVELS 2
	#define CMPXCHG cmpxchg
#else
	#error Invalid PTTYPE value
#endif

#define gpte_to_gfn FNAME(gpte_to_gfn)
#define gpte_to_gfn_pde FNAME(gpte_to_gfn_pde)

/*
 * The guest_walker structure emulates the behavior of the hardware page
 * table walker.
 */
struct guest_walker {
	int level;
	gfn_t table_gfn[PT_MAX_FULL_LEVELS];
	pt_element_t ptes[PT_MAX_FULL_LEVELS];
	gpa_t pte_gpa[PT_MAX_FULL_LEVELS];
	unsigned pt_access;
	unsigned pte_access;
	gfn_t gfn;
	u32 error_code;
};

struct shadow_walker {
	struct kvm_shadow_walk walker;
	struct guest_walker *guest_walker;
	int user_fault;
	int write_fault;
	int largepage;
	int *ptwrite;
	pfn_t pfn;
	u64 *sptep;
};

static gfn_t gpte_to_gfn(pt_element_t gpte)
{
	return (gpte & PT_BASE_ADDR_MASK) >> PAGE_SHIFT;
}

static gfn_t gpte_to_gfn_pde(pt_element_t gpte)
{
	return (gpte & PT_DIR_BASE_ADDR_MASK) >> PAGE_SHIFT;
}

static bool FNAME(cmpxchg_gpte)(struct kvm *kvm,
			 gfn_t table_gfn, unsigned index,
			 pt_element_t orig_pte, pt_element_t new_pte)
{
	pt_element_t ret;
	pt_element_t *table;
	struct page *page;

	down_read(&current->mm->mmap_sem);
	page = gfn_to_page(kvm, table_gfn);
	up_read(&current->mm->mmap_sem);

	table = kmap_atomic(page, KM_USER0);

	ret = CMPXCHG(&table[index], orig_pte, new_pte);

	kunmap_atomic(table, KM_USER0);

	kvm_release_page_dirty(page);

	return (ret != orig_pte);
}

static unsigned FNAME(gpte_access)(struct kvm_vcpu *vcpu, pt_element_t gpte)
{
	unsigned access;

	access = (gpte & (PT_WRITABLE_MASK | PT_USER_MASK)) | ACC_EXEC_MASK;
#if PTTYPE == 64
	if (is_nx(vcpu))
		access &= ~(gpte >> PT64_NX_SHIFT);
#endif
	return access;
}

/*
 * Fetch a guest pte for a guest virtual address
 */
static int FNAME(walk_addr)(struct guest_walker *walker,
			    struct kvm_vcpu *vcpu, gva_t addr,
			    int write_fault, int user_fault, int fetch_fault)
{
	pt_element_t pte;
	gfn_t table_gfn;
	unsigned index, pt_access, pte_access;
	gpa_t pte_gpa;

	pgprintk("%s: addr %lx\n", __func__, addr);
walk:
	walker->level = vcpu->arch.mmu.root_level;
	pte = vcpu->arch.cr3;
#if PTTYPE == 64
	if (!is_long_mode(vcpu)) {
		pte = vcpu->arch.pdptrs[(addr >> 30) & 3];
		if (!is_present_pte(pte))
			goto not_present;
		--walker->level;
	}
#endif
	ASSERT((!is_long_mode(vcpu) && is_pae(vcpu)) ||
	       (vcpu->arch.cr3 & CR3_NONPAE_RESERVED_BITS) == 0);

	pt_access = ACC_ALL;

	for (;;) {
		index = PT_INDEX(addr, walker->level);

		table_gfn = gpte_to_gfn(pte);
		pte_gpa = gfn_to_gpa(table_gfn);
		pte_gpa += index * sizeof(pt_element_t);
		walker->table_gfn[walker->level - 1] = table_gfn;
		walker->pte_gpa[walker->level - 1] = pte_gpa;
		pgprintk("%s: table_gfn[%d] %lx\n", __func__,
			 walker->level - 1, table_gfn);

		kvm_read_guest(vcpu->kvm, pte_gpa, &pte, sizeof(pte));

		if (!is_present_pte(pte))
			goto not_present;

		if (write_fault && !is_writeble_pte(pte))
			if (user_fault || is_write_protection(vcpu))
				goto access_error;

		if (user_fault && !(pte & PT_USER_MASK))
			goto access_error;

#if PTTYPE == 64
		if (fetch_fault && is_nx(vcpu) && (pte & PT64_NX_MASK))
			goto access_error;
#endif

		if (!(pte & PT_ACCESSED_MASK)) {
			mark_page_dirty(vcpu->kvm, table_gfn);
			if (FNAME(cmpxchg_gpte)(vcpu->kvm, table_gfn,
			    index, pte, pte|PT_ACCESSED_MASK))
				goto walk;
			pte |= PT_ACCESSED_MASK;
		}

		pte_access = pt_access & FNAME(gpte_access)(vcpu, pte);

		walker->ptes[walker->level - 1] = pte;

		if (walker->level == PT_PAGE_TABLE_LEVEL) {
			walker->gfn = gpte_to_gfn(pte);
			break;
		}

		if (walker->level == PT_DIRECTORY_LEVEL
		    && (pte & PT_PAGE_SIZE_MASK)
		    && (PTTYPE == 64 || is_pse(vcpu))) {
			walker->gfn = gpte_to_gfn_pde(pte);
			walker->gfn += PT_INDEX(addr, PT_PAGE_TABLE_LEVEL);
			if (PTTYPE == 32 && is_cpuid_PSE36())
				walker->gfn += pse36_gfn_delta(pte);
			break;
		}

		pt_access = pte_access;
		--walker->level;
	}

	if (write_fault && !is_dirty_pte(pte)) {
		bool ret;

		mark_page_dirty(vcpu->kvm, table_gfn);
		ret = FNAME(cmpxchg_gpte)(vcpu->kvm, table_gfn, index, pte,
			    pte|PT_DIRTY_MASK);
		if (ret)
			goto walk;
		pte |= PT_DIRTY_MASK;
		kvm_mmu_pte_write(vcpu, pte_gpa, (u8 *)&pte, sizeof(pte));
		walker->ptes[walker->level - 1] = pte;
	}

	walker->pt_access = pt_access;
	walker->pte_access = pte_access;
	pgprintk("%s: pte %llx pte_access %x pt_access %x\n",
		 __func__, (u64)pte, pt_access, pte_access);
	return 1;

not_present:
	walker->error_code = 0;
	goto err;

access_error:
	walker->error_code = PFERR_PRESENT_MASK;

err:
	if (write_fault)
		walker->error_code |= PFERR_WRITE_MASK;
	if (user_fault)
		walker->error_code |= PFERR_USER_MASK;
	if (fetch_fault)
		walker->error_code |= PFERR_FETCH_MASK;
	return 0;
}

static void FNAME(update_pte)(struct kvm_vcpu *vcpu, struct kvm_mmu_page *page,
			      u64 *spte, const void *pte)
{
	pt_element_t gpte;
	unsigned pte_access;
	pfn_t pfn;
	int largepage = vcpu->arch.update_pte.largepage;

	gpte = *(const pt_element_t *)pte;
	if (~gpte & (PT_PRESENT_MASK | PT_ACCESSED_MASK)) {
		if (!is_present_pte(gpte))
			set_shadow_pte(spte, shadow_notrap_nonpresent_pte);
		return;
	}
	pgprintk("%s: gpte %llx spte %p\n", __func__, (u64)gpte, spte);
	pte_access = page->role.access & FNAME(gpte_access)(vcpu, gpte);
	if (gpte_to_gfn(gpte) != vcpu->arch.update_pte.gfn)
		return;
	pfn = vcpu->arch.update_pte.pfn;
	if (is_error_pfn(pfn))
		return;
	if (mmu_notifier_retry(vcpu, vcpu->arch.update_pte.mmu_seq))
		return;
	kvm_get_pfn(pfn);
	mmu_set_spte(vcpu, spte, page->role.access, pte_access, 0, 0,
		     gpte & PT_DIRTY_MASK, NULL, largepage, gpte_to_gfn(gpte),
		     pfn, true);
}

/*
 * Fetch a shadow pte for a specific level in the paging hierarchy.
 */
static int FNAME(shadow_walk_entry)(struct kvm_shadow_walk *_sw,
				    struct kvm_vcpu *vcpu, gva_t addr,
				    u64 *sptep, int level)
{
	struct shadow_walker *sw =
		container_of(_sw, struct shadow_walker, walker);
	struct guest_walker *gw = sw->guest_walker;
	unsigned access = gw->pt_access;
	struct kvm_mmu_page *shadow_page;
	u64 spte;
	int metaphysical;
	gfn_t table_gfn;
	int r;
	pt_element_t curr_pte;

	if (level == PT_PAGE_TABLE_LEVEL
	    || (sw->largepage && level == PT_DIRECTORY_LEVEL)) {
		mmu_set_spte(vcpu, sptep, access, gw->pte_access & access,
			     sw->user_fault, sw->write_fault,
			     gw->ptes[gw->level-1] & PT_DIRTY_MASK,
			     sw->ptwrite, sw->largepage, gw->gfn, sw->pfn,
			     false);
		sw->sptep = sptep;
		return 1;
	}

	if (is_shadow_present_pte(*sptep) && !is_large_pte(*sptep))
		return 0;

	if (is_large_pte(*sptep))
		rmap_remove(vcpu->kvm, sptep);

	if (level == PT_DIRECTORY_LEVEL && gw->level == PT_DIRECTORY_LEVEL) {
		metaphysical = 1;
		if (!is_dirty_pte(gw->ptes[level - 1]))
			access &= ~ACC_WRITE_MASK;
		table_gfn = gpte_to_gfn(gw->ptes[level - 1]);
	} else {
		metaphysical = 0;
		table_gfn = gw->table_gfn[level - 2];
	}
	shadow_page = kvm_mmu_get_page(vcpu, table_gfn, addr, level-1,
				       metaphysical, access, sptep);
	if (!metaphysical) {
		r = kvm_read_guest_atomic(vcpu->kvm, gw->pte_gpa[level - 2],
					  &curr_pte, sizeof(curr_pte));
		if (r || curr_pte != gw->ptes[level - 2]) {
			kvm_release_pfn_clean(sw->pfn);
			sw->sptep = NULL;
			return 1;
		}
	}

	spte = __pa(shadow_page->spt) | PT_PRESENT_MASK | PT_ACCESSED_MASK
		| PT_WRITABLE_MASK | PT_USER_MASK;
	*sptep = spte;
	return 0;
}

static u64 *FNAME(fetch)(struct kvm_vcpu *vcpu, gva_t addr,
			 struct guest_walker *guest_walker,
			 int user_fault, int write_fault, int largepage,
			 int *ptwrite, pfn_t pfn)
{
	struct shadow_walker walker = {
		.walker = { .entry = FNAME(shadow_walk_entry), },
		.guest_walker = guest_walker,
		.user_fault = user_fault,
		.write_fault = write_fault,
		.largepage = largepage,
		.ptwrite = ptwrite,
		.pfn = pfn,
	};

	if (!is_present_pte(guest_walker->ptes[guest_walker->level - 1]))
		return NULL;

	walk_shadow(&walker.walker, vcpu, addr);

	return walker.sptep;
}

/*
 * Page fault handler.  There are several causes for a page fault:
 *   - there is no shadow pte for the guest pte
 *   - write access through a shadow pte marked read only so that we can set
 *     the dirty bit
 *   - write access to a shadow pte marked read only so we can update the page
 *     dirty bitmap, when userspace requests it
 *   - mmio access; in this case we will never install a present shadow pte
 *   - normal guest page fault due to the guest pte marked not present, not
 *     writable, or not executable
 *
 *  Returns: 1 if we need to emulate the instruction, 0 otherwise, or
 *           a negative value on error.
 */
static int FNAME(page_fault)(struct kvm_vcpu *vcpu, gva_t addr,
			       u32 error_code)
{
	int write_fault = error_code & PFERR_WRITE_MASK;
	int user_fault = error_code & PFERR_USER_MASK;
	int fetch_fault = error_code & PFERR_FETCH_MASK;
	struct guest_walker walker;
	u64 *shadow_pte;
	int write_pt = 0;
	int r;
	pfn_t pfn;
	int largepage = 0;
	unsigned long mmu_seq;

	pgprintk("%s: addr %lx err %x\n", __func__, addr, error_code);
	kvm_mmu_audit(vcpu, "pre page fault");

	r = mmu_topup_memory_caches(vcpu);
	if (r)
		return r;

	/*
	 * Look up the shadow pte for the faulting address.
	 */
	r = FNAME(walk_addr)(&walker, vcpu, addr, write_fault, user_fault,
			     fetch_fault);

	/*
	 * The page is not mapped by the guest.  Let the guest handle it.
	 */
	if (!r) {
		pgprintk("%s: guest page fault\n", __func__);
		inject_page_fault(vcpu, addr, walker.error_code);
		vcpu->arch.last_pt_write_count = 0; /* reset fork detector */
		return 0;
	}

	down_read(&current->mm->mmap_sem);
	if (walker.level == PT_DIRECTORY_LEVEL) {
		gfn_t large_gfn;
		large_gfn = walker.gfn & ~(KVM_PAGES_PER_HPAGE-1);
		if (is_largepage_backed(vcpu, large_gfn)) {
			walker.gfn = large_gfn;
			largepage = 1;
		}
	}
	mmu_seq = vcpu->kvm->mmu_notifier_seq;
	/* implicit mb(), we'll read before PT lock is unlocked */
	pfn = gfn_to_pfn(vcpu->kvm, walker.gfn);
	up_read(&current->mm->mmap_sem);

	/* mmio */
	if (is_error_pfn(pfn)) {
		pgprintk("gfn %lx is mmio\n", walker.gfn);
		kvm_release_pfn_clean(pfn);
		return 1;
	}

	spin_lock(&vcpu->kvm->mmu_lock);
	if (mmu_notifier_retry(vcpu, mmu_seq))
		goto out_unlock;
	kvm_mmu_free_some_pages(vcpu);
	shadow_pte = FNAME(fetch)(vcpu, addr, &walker, user_fault, write_fault,
				  largepage, &write_pt, pfn);

	pgprintk("%s: shadow pte %p %llx ptwrite %d\n", __func__,
		 shadow_pte, *shadow_pte, write_pt);

	if (!write_pt)
		vcpu->arch.last_pt_write_count = 0; /* reset fork detector */

	++vcpu->stat.pf_fixed;
	kvm_mmu_audit(vcpu, "post page fault (fixed)");
	spin_unlock(&vcpu->kvm->mmu_lock);

	return write_pt;

out_unlock:
	spin_unlock(&vcpu->kvm->mmu_lock);
	kvm_release_pfn_clean(pfn);
	return 0;
}

static gpa_t FNAME(gva_to_gpa)(struct kvm_vcpu *vcpu, gva_t vaddr)
{
	struct guest_walker walker;
	gpa_t gpa = UNMAPPED_GVA;
	int r;

	r = FNAME(walk_addr)(&walker, vcpu, vaddr, 0, 0, 0);

	if (r) {
		gpa = gfn_to_gpa(walker.gfn);
		gpa |= vaddr & ~PAGE_MASK;
	}

	return gpa;
}

static void FNAME(prefetch_page)(struct kvm_vcpu *vcpu,
				 struct kvm_mmu_page *sp)
{
	int i, j, offset, r;
	pt_element_t pt[256 / sizeof(pt_element_t)];
	gpa_t pte_gpa;

	if (sp->role.metaphysical
	    || (PTTYPE == 32 && sp->role.level > PT_PAGE_TABLE_LEVEL)) {
		nonpaging_prefetch_page(vcpu, sp);
		return;
	}

	pte_gpa = gfn_to_gpa(sp->gfn);
	if (PTTYPE == 32) {
		offset = sp->role.quadrant << PT64_LEVEL_BITS;
		pte_gpa += offset * sizeof(pt_element_t);
	}

	for (i = 0; i < PT64_ENT_PER_PAGE; i += ARRAY_SIZE(pt)) {
		r = kvm_read_guest_atomic(vcpu->kvm, pte_gpa, pt, sizeof pt);
		pte_gpa += ARRAY_SIZE(pt) * sizeof(pt_element_t);
		for (j = 0; j < ARRAY_SIZE(pt); ++j)
			if (r || is_present_pte(pt[j]))
				sp->spt[i+j] = shadow_trap_nonpresent_pte;
			else
				sp->spt[i+j] = shadow_notrap_nonpresent_pte;
	}
}

#undef pt_element_t
#undef guest_walker
#undef shadow_walker
#undef FNAME
#undef PT_BASE_ADDR_MASK
#undef PT_INDEX
#undef PT_LEVEL_MASK
#undef PT_DIR_BASE_ADDR_MASK
#undef PT_LEVEL_BITS
#undef PT_MAX_FULL_LEVELS
#undef gpte_to_gfn
#undef gpte_to_gfn_pde
#undef CMPXCHG