[PATCH] KVM: MMU: Shadow page table caching
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>
diff --git a/drivers/kvm/paging_tmpl.h b/drivers/kvm/paging_tmpl.h
index 11cac9d..f7cce44 100644
--- a/drivers/kvm/paging_tmpl.h
+++ b/drivers/kvm/paging_tmpl.h
@@ -32,6 +32,11 @@
#define SHADOW_PT_INDEX(addr, level) PT64_INDEX(addr, level)
#define PT_LEVEL_MASK(level) PT64_LEVEL_MASK(level)
#define PT_PTE_COPY_MASK PT64_PTE_COPY_MASK
+ #ifdef CONFIG_X86_64
+ #define PT_MAX_FULL_LEVELS 4
+ #else
+ #define PT_MAX_FULL_LEVELS 2
+ #endif
#elif PTTYPE == 32
#define pt_element_t u32
#define guest_walker guest_walker32
@@ -42,6 +47,7 @@
#define SHADOW_PT_INDEX(addr, level) PT64_INDEX(addr, level)
#define PT_LEVEL_MASK(level) PT32_LEVEL_MASK(level)
#define PT_PTE_COPY_MASK PT32_PTE_COPY_MASK
+ #define PT_MAX_FULL_LEVELS 2
#else
#error Invalid PTTYPE value
#endif
@@ -52,7 +58,7 @@
*/
struct guest_walker {
int level;
- gfn_t table_gfn;
+ gfn_t table_gfn[PT_MAX_FULL_LEVELS];
pt_element_t *table;
pt_element_t *ptep;
pt_element_t inherited_ar;
@@ -68,7 +74,9 @@
struct kvm_memory_slot *slot;
pt_element_t *ptep;
pt_element_t root;
+ gfn_t table_gfn;
+ pgprintk("%s: addr %lx\n", __FUNCTION__, addr);
walker->level = vcpu->mmu.root_level;
walker->table = NULL;
root = vcpu->cr3;
@@ -81,8 +89,11 @@
--walker->level;
}
#endif
- walker->table_gfn = (root & PT64_BASE_ADDR_MASK) >> PAGE_SHIFT;
- slot = gfn_to_memslot(vcpu->kvm, walker->table_gfn);
+ table_gfn = (root & PT64_BASE_ADDR_MASK) >> PAGE_SHIFT;
+ walker->table_gfn[walker->level - 1] = table_gfn;
+ pgprintk("%s: table_gfn[%d] %lx\n", __FUNCTION__,
+ walker->level - 1, table_gfn);
+ slot = gfn_to_memslot(vcpu->kvm, table_gfn);
hpa = safe_gpa_to_hpa(vcpu, root & PT64_BASE_ADDR_MASK);
walker->table = kmap_atomic(pfn_to_page(hpa >> PAGE_SHIFT), KM_USER0);
@@ -111,12 +122,15 @@
if (walker->level != 3 || is_long_mode(vcpu))
walker->inherited_ar &= walker->table[index];
- walker->table_gfn = (*ptep & PT_BASE_ADDR_MASK) >> PAGE_SHIFT;
+ table_gfn = (*ptep & PT_BASE_ADDR_MASK) >> PAGE_SHIFT;
paddr = safe_gpa_to_hpa(vcpu, *ptep & PT_BASE_ADDR_MASK);
kunmap_atomic(walker->table, KM_USER0);
walker->table = kmap_atomic(pfn_to_page(paddr >> PAGE_SHIFT),
KM_USER0);
--walker->level;
+ walker->table_gfn[walker->level - 1 ] = table_gfn;
+ pgprintk("%s: table_gfn[%d] %lx\n", __FUNCTION__,
+ walker->level - 1, table_gfn);
}
walker->ptep = ptep;
}
@@ -181,6 +195,8 @@
u64 *shadow_ent = ((u64 *)__va(shadow_addr)) + index;
struct kvm_mmu_page *shadow_page;
u64 shadow_pte;
+ int metaphysical;
+ gfn_t table_gfn;
if (is_present_pte(*shadow_ent) || is_io_pte(*shadow_ent)) {
if (level == PT_PAGE_TABLE_LEVEL)
@@ -205,7 +221,17 @@
return shadow_ent;
}
- shadow_page = kvm_mmu_alloc_page(vcpu, shadow_ent);
+ if (level - 1 == PT_PAGE_TABLE_LEVEL
+ && walker->level == PT_DIRECTORY_LEVEL) {
+ metaphysical = 1;
+ table_gfn = (*guest_ent & PT_BASE_ADDR_MASK)
+ >> PAGE_SHIFT;
+ } else {
+ metaphysical = 0;
+ table_gfn = walker->table_gfn[level - 2];
+ }
+ shadow_page = kvm_mmu_get_page(vcpu, table_gfn, addr, level-1,
+ metaphysical, shadow_ent);
if (!shadow_page)
return ERR_PTR(-ENOMEM);
shadow_addr = shadow_page->page_hpa;
@@ -227,7 +253,8 @@
u64 *shadow_ent,
struct guest_walker *walker,
gva_t addr,
- int user)
+ int user,
+ int *write_pt)
{
pt_element_t *guest_ent;
int writable_shadow;
@@ -264,6 +291,12 @@
}
gfn = (*guest_ent & PT64_BASE_ADDR_MASK) >> PAGE_SHIFT;
+ if (kvm_mmu_lookup_page(vcpu, gfn)) {
+ pgprintk("%s: found shadow page for %lx, marking ro\n",
+ __FUNCTION__, gfn);
+ *write_pt = 1;
+ return 0;
+ }
mark_page_dirty(vcpu->kvm, gfn);
*shadow_ent |= PT_WRITABLE_MASK;
*guest_ent |= PT_DIRTY_MASK;
@@ -294,7 +327,9 @@
struct guest_walker walker;
u64 *shadow_pte;
int fixed;
+ int write_pt = 0;
+ pgprintk("%s: addr %lx err %x\n", __FUNCTION__, addr, error_code);
/*
* Look up the shadow pte for the faulting address.
*/
@@ -302,6 +337,7 @@
FNAME(walk_addr)(&walker, vcpu, addr);
shadow_pte = FNAME(fetch)(vcpu, addr, &walker);
if (IS_ERR(shadow_pte)) { /* must be -ENOMEM */
+ printk("%s: oom\n", __FUNCTION__);
nonpaging_flush(vcpu);
FNAME(release_walker)(&walker);
continue;
@@ -313,20 +349,27 @@
* The page is not mapped by the guest. Let the guest handle it.
*/
if (!shadow_pte) {
+ pgprintk("%s: not mapped\n", __FUNCTION__);
inject_page_fault(vcpu, addr, error_code);
FNAME(release_walker)(&walker);
return 0;
}
+ pgprintk("%s: shadow pte %p %llx\n", __FUNCTION__,
+ shadow_pte, *shadow_pte);
+
/*
* Update the shadow pte.
*/
if (write_fault)
fixed = FNAME(fix_write_pf)(vcpu, shadow_pte, &walker, addr,
- user_fault);
+ user_fault, &write_pt);
else
fixed = fix_read_pf(shadow_pte);
+ pgprintk("%s: updated shadow pte %p %llx\n", __FUNCTION__,
+ shadow_pte, *shadow_pte);
+
FNAME(release_walker)(&walker);
/*
@@ -344,14 +387,14 @@
/*
* pte not present, guest page fault.
*/
- if (pte_present && !fixed) {
+ if (pte_present && !fixed && !write_pt) {
inject_page_fault(vcpu, addr, error_code);
return 0;
}
++kvm_stat.pf_fixed;
- return 0;
+ return write_pt;
}
static gpa_t FNAME(gva_to_gpa)(struct kvm_vcpu *vcpu, gva_t vaddr)
@@ -395,3 +438,4 @@
#undef PT_PTE_COPY_MASK
#undef PT_NON_PTE_COPY_MASK
#undef PT_DIR_BASE_ADDR_MASK
+#undef PT_MAX_FULL_LEVELS
