KVM: MMU: Add generic shadow walker

We currently walk the shadow page tables in two places: direct map (for
real mode and two dimensional paging) and paging mode shadow.  Since we
anticipate requiring a third walk (for invlpg), it makes sense to have
a generic facility for shadow walk.

This patch adds such a shadow walker, walks the page tables and calls a
method for every spte encountered.  The method can examine the spte,
modify it, or even instantiate it.  The walk can be aborted by returning
nonzero from the method.

Signed-off-by: Avi Kivity <avi@qumranet.com>

1 files changed, 34 insertions, 0 deletions

diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
index 72f739aa8623..8b95cf748b53 100644
--- a/arch/x86/kvm/mmu.c
+++ b/arch/x86/kvm/mmu.c
@@ -142,6 +142,11 @@ struct kvm_rmap_desc {
         struct kvm_rmap_desc *more;
 };
 
+struct kvm_shadow_walk {
+        int (*entry)(struct kvm_shadow_walk *walk, struct kvm_vcpu *vcpu,
+                     gva_t addr, u64 *spte, int level);
+};
+
 static struct kmem_cache *pte_chain_cache;
 static struct kmem_cache *rmap_desc_cache;
 static struct kmem_cache *mmu_page_header_cache;
@@ -935,6 +940,35 @@ static struct kvm_mmu_page *kvm_mmu_get_page(struct kvm_vcpu *vcpu,
         return sp;
 }
 
+static int walk_shadow(struct kvm_shadow_walk *walker,
+                       struct kvm_vcpu *vcpu, gva_t addr)
+{
+        hpa_t shadow_addr;
+        int level;
+        int r;
+        u64 *sptep;
+        unsigned index;
+
+        shadow_addr = vcpu->arch.mmu.root_hpa;
+        level = vcpu->arch.mmu.shadow_root_level;
+        if (level == PT32E_ROOT_LEVEL) {
+                shadow_addr = vcpu->arch.mmu.pae_root[(addr >> 30) & 3];
+                shadow_addr &= PT64_BASE_ADDR_MASK;
+                --level;
+        }
+
+        while (level >= PT_PAGE_TABLE_LEVEL) {
+                index = SHADOW_PT_INDEX(addr, level);
+                sptep = ((u64 *)__va(shadow_addr)) + index;
+                r = walker->entry(walker, vcpu, addr, sptep, level);
+                if (r)
+                        return r;
+                shadow_addr = *sptep & PT64_BASE_ADDR_MASK;
+                --level;
+        }
+        return 0;
+}
+
 static void kvm_mmu_page_unlink_children(struct kvm *kvm,
                                          struct kvm_mmu_page *sp)
 {