[PATCH 39/41] KVM: Add physical memory aliasing feature

[Avi Kivity]

With this, we can specify that accesses to one physical memory range will
be remapped to another.  This is useful for the vga window at 0xa0000 which
is used as a movable window into the (much larger) framebuffer.

Signed-off-by: Avi Kivity <avi@xxxxxxxxxxxx>
---
 drivers/kvm/kvm.h      |    9 +++++
 drivers/kvm/kvm_main.c |   89 ++++++++++++++++++++++++++++++++++++++++++++++--
 include/linux/kvm.h    |   10 +++++-
 3 files changed, 104 insertions(+), 4 deletions(-)

diff --git a/drivers/kvm/kvm.h b/drivers/kvm/kvm.h
index d19985a..fceeb84 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 aaaf306..56ddbc1 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];
@@ -2503,6 +2575,17 @@ 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 728b24c..da9b23f 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
-- 
1.5.0.5

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