[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>

1 files changed, 53 insertions, 9 deletions

diff --git a/drivers/kvm/paging_tmpl.h b/drivers/kvm/paging_tmpl.h
index 11cac9ddf26a..f7cce443ca6f 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 @@ static void FNAME(walk_addr)(struct guest_walker *walker,
         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 @@ static void FNAME(walk_addr)(struct guest_walker *walker,
                 --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 @@ static void FNAME(walk_addr)(struct guest_walker *walker,
 
                 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 @@ static u64 *FNAME(fetch)(struct kvm_vcpu *vcpu, gva_t addr,
                 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 @@ static u64 *FNAME(fetch)(struct kvm_vcpu *vcpu, gva_t addr,
                         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 @@ static int FNAME(fix_write_pf)(struct kvm_vcpu *vcpu,
                                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 @@ static int FNAME(fix_write_pf)(struct kvm_vcpu *vcpu,
         }
 
         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 @@ static int FNAME(page_fault)(struct kvm_vcpu *vcpu, gva_t addr,
         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 @@ static int FNAME(page_fault)(struct kvm_vcpu *vcpu, gva_t addr,
                 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 @@ static int FNAME(page_fault)(struct kvm_vcpu *vcpu, gva_t addr,
          * 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 @@ static int FNAME(page_fault)(struct kvm_vcpu *vcpu, gva_t addr,
         /*
          * 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 @@ static gpa_t FNAME(gva_to_gpa)(struct kvm_vcpu *vcpu, gva_t vaddr)
 #undef PT_PTE_COPY_MASK
 #undef PT_NON_PTE_COPY_MASK
 #undef PT_DIR_BASE_ADDR_MASK
+#undef PT_MAX_FULL_LEVELS