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[PATCH] KVM: MMU: Shadow page table caching
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Define a hashtable for caching shadow page tables. Look up the cache on
context switch (cr3 change) or during page faults.

The key to the cache is a combination of
- the guest page table frame number
- the number of paging levels in the guest
   * we can cache real mode, 32-bit mode, pae, and long mode page
     tables simultaneously.  this is useful for smp bootup.
- the guest page table table
   * some kernels use a page as both a page table and a page directory.  this
     allows multiple shadow pages to exist for that page, one per level
- the "quadrant"
   * 32-bit mode page tables span 4MB, whereas a shadow page table spans
     2MB.  similarly, a 32-bit page directory spans 4GB, while a shadow
     page directory spans 1GB.  the quadrant allows caching up to 4 shadow page
     tables for one guest page in one level.
- a "metaphysical" bit
   * for real mode, and for pse pages, there is no guest page table, so set
     the bit to avoid write protecting the page.

Signed-off-by: Avi Kivity <avi@qumranet.com>
Acked-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
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@avikivity
avikivity authored and Linus Torvalds committed Jan 6, 2007
1 parent 25c0de2 commit cea0f0e
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Showing 3 changed files with 280 additions and 34 deletions.
45 changes: 44 additions & 1 deletion drivers/kvm/kvm.h
View file
Original file line number Diff line number Diff line change
Expand Up @@ -89,14 +89,53 @@ typedef unsigned long hva_t;
typedef u64 hpa_t;
typedef unsigned long hfn_t;

#define NR_PTE_CHAIN_ENTRIES 5

struct kvm_pte_chain {
u64 *parent_ptes[NR_PTE_CHAIN_ENTRIES];
struct hlist_node link;
};

/*
* kvm_mmu_page_role, below, is defined as:
*
* bits 0:3 - total guest paging levels (2-4, or zero for real mode)
* bits 4:7 - page table level for this shadow (1-4)
* bits 8:9 - page table quadrant for 2-level guests
* bit 16 - "metaphysical" - gfn is not a real page (huge page/real mode)
*/
union kvm_mmu_page_role {
unsigned word;
struct {
unsigned glevels : 4;
unsigned level : 4;
unsigned quadrant : 2;
unsigned pad_for_nice_hex_output : 6;
unsigned metaphysical : 1;
};
};

struct kvm_mmu_page {
struct list_head link;
struct hlist_node hash_link;

/*
* The following two entries are used to key the shadow page in the
* hash table.
*/
gfn_t gfn;
union kvm_mmu_page_role role;

hpa_t page_hpa;
unsigned long slot_bitmap; /* One bit set per slot which has memory
* in this shadow page.
*/
int global; /* Set if all ptes in this page are global */
u64 *parent_pte;
int multimapped; /* More than one parent_pte? */
union {
u64 *parent_pte; /* !multimapped */
struct hlist_head parent_ptes; /* multimapped, kvm_pte_chain */
};
};

struct vmcs {
Expand Down Expand Up @@ -235,7 +274,11 @@ struct kvm {
spinlock_t lock; /* protects everything except vcpus */
int nmemslots;
struct kvm_memory_slot memslots[KVM_MEMORY_SLOTS];
/*
* Hash table of struct kvm_mmu_page.
*/
struct list_head active_mmu_pages;
struct hlist_head mmu_page_hash[KVM_NUM_MMU_PAGES];
struct kvm_vcpu vcpus[KVM_MAX_VCPUS];
int memory_config_version;
int busy;
Expand Down
207 changes: 183 additions & 24 deletions drivers/kvm/mmu.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -26,17 +26,19 @@
#include "vmx.h"
#include "kvm.h"

#define pgprintk(x...) do { } while (0)
#define rmap_printk(x...) do { } while (0)
#define pgprintk(x...) do { printk(x); } while (0)
#define rmap_printk(x...) do { printk(x); } while (0)

#define ASSERT(x) \
if (!(x)) { \
printk(KERN_WARNING "assertion failed %s:%d: %s\n", \
__FILE__, __LINE__, #x); \
}

#define PT64_ENT_PER_PAGE 512
#define PT32_ENT_PER_PAGE 1024
#define PT64_PT_BITS 9
#define PT64_ENT_PER_PAGE (1 << PT64_PT_BITS)
#define PT32_PT_BITS 10
#define PT32_ENT_PER_PAGE (1 << PT32_PT_BITS)

#define PT_WRITABLE_SHIFT 1

Expand Down Expand Up @@ -292,6 +294,11 @@ static int is_empty_shadow_page(hpa_t page_hpa)
return 1;
}

static unsigned kvm_page_table_hashfn(gfn_t gfn)
{
return gfn;
}

static struct kvm_mmu_page *kvm_mmu_alloc_page(struct kvm_vcpu *vcpu,
u64 *parent_pte)
{
Expand All @@ -306,10 +313,147 @@ static struct kvm_mmu_page *kvm_mmu_alloc_page(struct kvm_vcpu *vcpu,
ASSERT(is_empty_shadow_page(page->page_hpa));
page->slot_bitmap = 0;
page->global = 1;
page->multimapped = 0;
page->parent_pte = parent_pte;
return page;
}

static void mmu_page_add_parent_pte(struct kvm_mmu_page *page, u64 *parent_pte)
{
struct kvm_pte_chain *pte_chain;
struct hlist_node *node;
int i;

if (!parent_pte)
return;
if (!page->multimapped) {
u64 *old = page->parent_pte;

if (!old) {
page->parent_pte = parent_pte;
return;
}
page->multimapped = 1;
pte_chain = kzalloc(sizeof(struct kvm_pte_chain), GFP_NOWAIT);
BUG_ON(!pte_chain);
INIT_HLIST_HEAD(&page->parent_ptes);
hlist_add_head(&pte_chain->link, &page->parent_ptes);
pte_chain->parent_ptes[0] = old;
}
hlist_for_each_entry(pte_chain, node, &page->parent_ptes, link) {
if (pte_chain->parent_ptes[NR_PTE_CHAIN_ENTRIES-1])
continue;
for (i = 0; i < NR_PTE_CHAIN_ENTRIES; ++i)
if (!pte_chain->parent_ptes[i]) {
pte_chain->parent_ptes[i] = parent_pte;
return;
}
}
pte_chain = kzalloc(sizeof(struct kvm_pte_chain), GFP_NOWAIT);
BUG_ON(!pte_chain);
hlist_add_head(&pte_chain->link, &page->parent_ptes);
pte_chain->parent_ptes[0] = parent_pte;
}

static void mmu_page_remove_parent_pte(struct kvm_mmu_page *page,
u64 *parent_pte)
{
struct kvm_pte_chain *pte_chain;
struct hlist_node *node;
int i;

if (!page->multimapped) {
BUG_ON(page->parent_pte != parent_pte);
page->parent_pte = NULL;
return;
}
hlist_for_each_entry(pte_chain, node, &page->parent_ptes, link)
for (i = 0; i < NR_PTE_CHAIN_ENTRIES; ++i) {
if (!pte_chain->parent_ptes[i])
break;
if (pte_chain->parent_ptes[i] != parent_pte)
continue;
while (i + 1 < NR_PTE_CHAIN_ENTRIES) {
pte_chain->parent_ptes[i]
= pte_chain->parent_ptes[i + 1];
++i;
}
pte_chain->parent_ptes[i] = NULL;
return;
}
BUG();
}

static struct kvm_mmu_page *kvm_mmu_lookup_page(struct kvm_vcpu *vcpu,
gfn_t gfn)
{
unsigned index;
struct hlist_head *bucket;
struct kvm_mmu_page *page;
struct hlist_node *node;

pgprintk("%s: looking for gfn %lx\n", __FUNCTION__, gfn);
index = kvm_page_table_hashfn(gfn) % KVM_NUM_MMU_PAGES;
bucket = &vcpu->kvm->mmu_page_hash[index];
hlist_for_each_entry(page, node, bucket, hash_link)
if (page->gfn == gfn && !page->role.metaphysical) {
pgprintk("%s: found role %x\n",
__FUNCTION__, page->role.word);
return page;
}
return NULL;
}

static struct kvm_mmu_page *kvm_mmu_get_page(struct kvm_vcpu *vcpu,
gfn_t gfn,
gva_t gaddr,
unsigned level,
int metaphysical,
u64 *parent_pte)
{
union kvm_mmu_page_role role;
unsigned index;
unsigned quadrant;
struct hlist_head *bucket;
struct kvm_mmu_page *page;
struct hlist_node *node;

role.word = 0;
role.glevels = vcpu->mmu.root_level;
role.level = level;
role.metaphysical = metaphysical;
if (vcpu->mmu.root_level <= PT32_ROOT_LEVEL) {
quadrant = gaddr >> (PAGE_SHIFT + (PT64_PT_BITS * level));
quadrant &= (1 << ((PT32_PT_BITS - PT64_PT_BITS) * level)) - 1;
role.quadrant = quadrant;
}
pgprintk("%s: looking gfn %lx role %x\n", __FUNCTION__,
gfn, role.word);
index = kvm_page_table_hashfn(gfn) % KVM_NUM_MMU_PAGES;
bucket = &vcpu->kvm->mmu_page_hash[index];
hlist_for_each_entry(page, node, bucket, hash_link)
if (page->gfn == gfn && page->role.word == role.word) {
mmu_page_add_parent_pte(page, parent_pte);
pgprintk("%s: found\n", __FUNCTION__);
return page;
}
page = kvm_mmu_alloc_page(vcpu, parent_pte);
if (!page)
return page;
pgprintk("%s: adding gfn %lx role %x\n", __FUNCTION__, gfn, role.word);
page->gfn = gfn;
page->role = role;
hlist_add_head(&page->hash_link, bucket);
return page;
}

static void kvm_mmu_put_page(struct kvm_vcpu *vcpu,
struct kvm_mmu_page *page,
u64 *parent_pte)
{
mmu_page_remove_parent_pte(page, parent_pte);
}

static void page_header_update_slot(struct kvm *kvm, void *pte, gpa_t gpa)
{
int slot = memslot_id(kvm, gfn_to_memslot(kvm, gpa >> PAGE_SHIFT));
Expand Down Expand Up @@ -389,11 +533,15 @@ static int nonpaging_map(struct kvm_vcpu *vcpu, gva_t v, hpa_t p)
for (; ; level--) {
u32 index = PT64_INDEX(v, level);
u64 *table;
u64 pte;

ASSERT(VALID_PAGE(table_addr));
table = __va(table_addr);

if (level == 1) {
pte = table[index];
if (is_present_pte(pte) && is_writeble_pte(pte))
return 0;
mark_page_dirty(vcpu->kvm, v >> PAGE_SHIFT);
page_header_update_slot(vcpu->kvm, table, v);
table[index] = p | PT_PRESENT_MASK | PT_WRITABLE_MASK |
Expand All @@ -404,8 +552,13 @@ static int nonpaging_map(struct kvm_vcpu *vcpu, gva_t v, hpa_t p)

if (table[index] == 0) {
struct kvm_mmu_page *new_table;
gfn_t pseudo_gfn;

new_table = kvm_mmu_alloc_page(vcpu, &table[index]);
pseudo_gfn = (v & PT64_DIR_BASE_ADDR_MASK)
>> PAGE_SHIFT;
new_table = kvm_mmu_get_page(vcpu, pseudo_gfn,
v, level - 1,
1, &table[index]);
if (!new_table) {
pgprintk("nonpaging_map: ENOMEM\n");
return -ENOMEM;
Expand All @@ -427,7 +580,6 @@ static void mmu_free_roots(struct kvm_vcpu *vcpu)
hpa_t root = vcpu->mmu.root_hpa;

ASSERT(VALID_PAGE(root));
release_pt_page_64(vcpu, root, PT64_ROOT_LEVEL);
vcpu->mmu.root_hpa = INVALID_PAGE;
return;
}
Expand All @@ -437,7 +589,6 @@ static void mmu_free_roots(struct kvm_vcpu *vcpu)

ASSERT(VALID_PAGE(root));
root &= PT64_BASE_ADDR_MASK;
release_pt_page_64(vcpu, root, PT32E_ROOT_LEVEL - 1);
vcpu->mmu.pae_root[i] = INVALID_PAGE;
}
vcpu->mmu.root_hpa = INVALID_PAGE;
Expand All @@ -446,13 +597,16 @@ static void mmu_free_roots(struct kvm_vcpu *vcpu)
static void mmu_alloc_roots(struct kvm_vcpu *vcpu)
{
int i;
gfn_t root_gfn;
root_gfn = vcpu->cr3 >> PAGE_SHIFT;

#ifdef CONFIG_X86_64
if (vcpu->mmu.shadow_root_level == PT64_ROOT_LEVEL) {
hpa_t root = vcpu->mmu.root_hpa;

ASSERT(!VALID_PAGE(root));
root = kvm_mmu_alloc_page(vcpu, NULL)->page_hpa;
root = kvm_mmu_get_page(vcpu, root_gfn, 0,
PT64_ROOT_LEVEL, 0, NULL)->page_hpa;
vcpu->mmu.root_hpa = root;
return;
}
Expand All @@ -461,7 +615,13 @@ static void mmu_alloc_roots(struct kvm_vcpu *vcpu)
hpa_t root = vcpu->mmu.pae_root[i];

ASSERT(!VALID_PAGE(root));
root = kvm_mmu_alloc_page(vcpu, NULL)->page_hpa;
if (vcpu->mmu.root_level == PT32E_ROOT_LEVEL)
root_gfn = vcpu->pdptrs[i] >> PAGE_SHIFT;
else if (vcpu->mmu.root_level == 0)
root_gfn = 0;
root = kvm_mmu_get_page(vcpu, root_gfn, i << 30,
PT32_ROOT_LEVEL, !is_paging(vcpu),
NULL)->page_hpa;
vcpu->mmu.pae_root[i] = root | PT_PRESENT_MASK;
}
vcpu->mmu.root_hpa = __pa(vcpu->mmu.pae_root);
Expand Down Expand Up @@ -529,37 +689,26 @@ static int nonpaging_init_context(struct kvm_vcpu *vcpu)
context->inval_page = nonpaging_inval_page;
context->gva_to_gpa = nonpaging_gva_to_gpa;
context->free = nonpaging_free;
context->root_level = PT32E_ROOT_LEVEL;
context->root_level = 0;
context->shadow_root_level = PT32E_ROOT_LEVEL;
mmu_alloc_roots(vcpu);
ASSERT(VALID_PAGE(context->root_hpa));
kvm_arch_ops->set_cr3(vcpu, context->root_hpa);
return 0;
}


static void kvm_mmu_flush_tlb(struct kvm_vcpu *vcpu)
{
struct kvm_mmu_page *page, *npage;

list_for_each_entry_safe(page, npage, &vcpu->kvm->active_mmu_pages,
link) {
if (page->global)
continue;

if (!page->parent_pte)
continue;

*page->parent_pte = 0;
release_pt_page_64(vcpu, page->page_hpa, 1);
}
++kvm_stat.tlb_flush;
kvm_arch_ops->tlb_flush(vcpu);
}

static void paging_new_cr3(struct kvm_vcpu *vcpu)
{
mmu_free_roots(vcpu);
mmu_alloc_roots(vcpu);
kvm_mmu_flush_tlb(vcpu);
kvm_arch_ops->set_cr3(vcpu, vcpu->mmu.root_hpa);
}

static void mark_pagetable_nonglobal(void *shadow_pte)
Expand All @@ -578,6 +727,16 @@ static inline void set_pte_common(struct kvm_vcpu *vcpu,
*shadow_pte |= access_bits << PT_SHADOW_BITS_OFFSET;
if (!dirty)
access_bits &= ~PT_WRITABLE_MASK;
if (access_bits & PT_WRITABLE_MASK) {
struct kvm_mmu_page *shadow;

shadow = kvm_mmu_lookup_page(vcpu, gaddr >> PAGE_SHIFT);
if (shadow)
pgprintk("%s: found shadow page for %lx, marking ro\n",
__FUNCTION__, (gfn_t)(gaddr >> PAGE_SHIFT));
if (shadow)
access_bits &= ~PT_WRITABLE_MASK;
}

if (access_bits & PT_WRITABLE_MASK)
mark_page_dirty(vcpu->kvm, gaddr >> PAGE_SHIFT);
Expand Down
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