3 files changed, 104 insertions, 4 deletions

diff --git a/drivers/kvm/kvm.h b/drivers/kvm/kvm.h
index d19985a5508a..fceeb840a255 100644
--- a/drivers/kvm/kvm.h
+++ b/drivers/kvm/kvm.h
@@ -51,6 +51,7 @@
 #define UNMAPPED_GVA (~(gpa_t)0)
 
 #define KVM_MAX_VCPUS 1
+#define KVM_ALIAS_SLOTS 4
 #define KVM_MEMORY_SLOTS 4
 #define KVM_NUM_MMU_PAGES 256
 #define KVM_MIN_FREE_MMU_PAGES 5
@@ -312,6 +313,12 @@ struct kvm_vcpu {
         struct kvm_cpuid_entry cpuid_entries[KVM_MAX_CPUID_ENTRIES];
 };
 
+struct kvm_mem_alias {
+        gfn_t base_gfn;
+        unsigned long npages;
+        gfn_t target_gfn;
+};
+
 struct kvm_memory_slot {
         gfn_t base_gfn;
         unsigned long npages;
@@ -322,6 +329,8 @@ struct kvm_memory_slot {
 
 struct kvm {
         spinlock_t lock; /* protects everything except vcpus */
+        int naliases;
+        struct kvm_mem_alias aliases[KVM_ALIAS_SLOTS];
         int nmemslots;
         struct kvm_memory_slot memslots[KVM_MEMORY_SLOTS];
         /*
diff --git a/drivers/kvm/kvm_main.c b/drivers/kvm/kvm_main.c
index a0ec5dda3305..e495855727e2 100644
--- a/drivers/kvm/kvm_main.c
+++ b/drivers/kvm/kvm_main.c
@@ -846,7 +846,73 @@ out:
         return r;
 }
 
-struct kvm_memory_slot *gfn_to_memslot(struct kvm *kvm, gfn_t gfn)
+/*
+ * Set a new alias region.  Aliases map a portion of physical memory into
+ * another portion.  This is useful for memory windows, for example the PC
+ * VGA region.
+ */
+static int kvm_vm_ioctl_set_memory_alias(struct kvm *kvm,
+                                         struct kvm_memory_alias *alias)
+{
+        int r, n;
+        struct kvm_mem_alias *p;
+
+        r = -EINVAL;
+        /* General sanity checks */
+        if (alias->memory_size & (PAGE_SIZE - 1))
+                goto out;
+        if (alias->guest_phys_addr & (PAGE_SIZE - 1))
+                goto out;
+        if (alias->slot >= KVM_ALIAS_SLOTS)
+                goto out;
+        if (alias->guest_phys_addr + alias->memory_size
+            < alias->guest_phys_addr)
+                goto out;
+        if (alias->target_phys_addr + alias->memory_size
+            < alias->target_phys_addr)
+                goto out;
+
+        spin_lock(&kvm->lock);
+
+        p = &kvm->aliases[alias->slot];
+        p->base_gfn = alias->guest_phys_addr >> PAGE_SHIFT;
+        p->npages = alias->memory_size >> PAGE_SHIFT;
+        p->target_gfn = alias->target_phys_addr >> PAGE_SHIFT;
+
+        for (n = KVM_ALIAS_SLOTS; n > 0; --n)
+                if (kvm->aliases[n - 1].npages)
+                        break;
+        kvm->naliases = n;
+
+        spin_unlock(&kvm->lock);
+
+        vcpu_load(&kvm->vcpus[0]);
+        spin_lock(&kvm->lock);
+        kvm_mmu_zap_all(&kvm->vcpus[0]);
+        spin_unlock(&kvm->lock);
+        vcpu_put(&kvm->vcpus[0]);
+
+        return 0;
+
+out:
+        return r;
+}
+
+static gfn_t unalias_gfn(struct kvm *kvm, gfn_t gfn)
+{
+        int i;
+        struct kvm_mem_alias *alias;
+
+        for (i = 0; i < kvm->naliases; ++i) {
+                alias = &kvm->aliases[i];
+                if (gfn >= alias->base_gfn
+                    && gfn < alias->base_gfn + alias->npages)
+                        return alias->target_gfn + gfn - alias->base_gfn;
+        }
+        return gfn;
+}
+
+static struct kvm_memory_slot *__gfn_to_memslot(struct kvm *kvm, gfn_t gfn)
 {
         int i;
 
@@ -859,13 +925,19 @@ struct kvm_memory_slot *gfn_to_memslot(struct kvm *kvm, gfn_t gfn)
         }
         return NULL;
 }
-EXPORT_SYMBOL_GPL(gfn_to_memslot);
+
+struct kvm_memory_slot *gfn_to_memslot(struct kvm *kvm, gfn_t gfn)
+{
+        gfn = unalias_gfn(kvm, gfn);
+        return __gfn_to_memslot(kvm, gfn);
+}
 
 struct page *gfn_to_page(struct kvm *kvm, gfn_t gfn)
 {
         struct kvm_memory_slot *slot;
 
-        slot = gfn_to_memslot(kvm, gfn);
+        gfn = unalias_gfn(kvm, gfn);
+        slot = __gfn_to_memslot(kvm, gfn);
         if (!slot)
                 return NULL;
         return slot->phys_mem[gfn - slot->base_gfn];
@@ -2512,6 +2584,17 @@ static long kvm_vm_ioctl(struct file *filp,
                         goto out;
                 break;
         }
+        case KVM_SET_MEMORY_ALIAS: {
+                struct kvm_memory_alias alias;
+
+                r = -EFAULT;
+                if (copy_from_user(&alias, argp, sizeof alias))
+                        goto out;
+                r = kvm_vm_ioctl_set_memory_alias(kvm, &alias);
+                if (r)
+                        goto out;
+                break;
+        }
         default:
                 ;
         }
diff --git a/include/linux/kvm.h b/include/linux/kvm.h
index 728b24cf5d77..da9b23fa4b6c 100644
--- a/include/linux/kvm.h
+++ b/include/linux/kvm.h
@@ -11,7 +11,7 @@
 #include <asm/types.h>
 #include <linux/ioctl.h>
 
-#define KVM_API_VERSION 9
+#define KVM_API_VERSION 10
 
 /*
  * Architectural interrupt line count, and the size of the bitmap needed
@@ -33,6 +33,13 @@ struct kvm_memory_region {
 /* for kvm_memory_region::flags */
 #define KVM_MEM_LOG_DIRTY_PAGES  1UL
 
+struct kvm_memory_alias {
+        __u32 slot;  /* this has a different namespace than memory slots */
+        __u32 flags;
+        __u64 guest_phys_addr;
+        __u64 memory_size;
+        __u64 target_phys_addr;
+};
 
 enum kvm_exit_reason {
         KVM_EXIT_UNKNOWN          = 0,
@@ -261,6 +268,7 @@ struct kvm_signal_mask {
  */
 #define KVM_CREATE_VCPU           _IO(KVMIO,  0x41)
 #define KVM_GET_DIRTY_LOG         _IOW(KVMIO, 0x42, struct kvm_dirty_log)
+#define KVM_SET_MEMORY_ALIAS      _IOW(KVMIO, 0x43, struct kvm_memory_alias)
 
 /*
  * ioctls for vcpu fds