[PATCH v10 2/9] KVM: Introduce per-page memory attributes

[Chao Peng]

In confidential computing usages, whether a page is private or shared is
necessary information for KVM to perform operations like page fault
handling, page zapping etc. There are other potential use cases for
per-page memory attributes, e.g. to make memory read-only (or no-exec,
or exec-only, etc.) without having to modify memslots.

Introduce two ioctls (advertised by KVM_CAP_MEMORY_ATTRIBUTES) to allow
userspace to operate on the per-page memory attributes.
  - KVM_SET_MEMORY_ATTRIBUTES to set the per-page memory attributes to
    a guest memory range.
  - KVM_GET_SUPPORTED_MEMORY_ATTRIBUTES to return the KVM supported
    memory attributes.

KVM internally uses xarray to store the per-page memory attributes.

Suggested-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Chao Peng <chao.p.peng@linux.intel.com>
Link: https://lore.kernel.org/all/Y2WB48kD0J4VGynX@google.com/
---
 Documentation/virt/kvm/api.rst | 63 ++++++++++++++++++++++++++++
 arch/x86/kvm/Kconfig           |  1 +
 include/linux/kvm_host.h       |  3 ++
 include/uapi/linux/kvm.h       | 17 ++++++++
 virt/kvm/Kconfig               |  3 ++
 virt/kvm/kvm_main.c            | 76 ++++++++++++++++++++++++++++++++++
 6 files changed, 163 insertions(+)

diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst
index 5617bc4f899f..bb2f709c0900 100644
--- a/Documentation/virt/kvm/api.rst
+++ b/Documentation/virt/kvm/api.rst
@@ -5952,6 +5952,59 @@ delivery must be provided via the "reg_aen" struct.
 The "pad" and "reserved" fields may be used for future extensions and should be
 set to 0s by userspace.
 
+4.138 KVM_GET_SUPPORTED_MEMORY_ATTRIBUTES
+-----------------------------------------
+
+:Capability: KVM_CAP_MEMORY_ATTRIBUTES
+:Architectures: x86
+:Type: vm ioctl
+:Parameters: u64 memory attributes bitmask(out)
+:Returns: 0 on success, <0 on error
+
+Returns supported memory attributes bitmask. Supported memory attributes will
+have the corresponding bits set in u64 memory attributes bitmask.
+
+The following memory attributes are defined::
+
+  #define KVM_MEMORY_ATTRIBUTE_READ              (1ULL << 0)
+  #define KVM_MEMORY_ATTRIBUTE_WRITE             (1ULL << 1)
+  #define KVM_MEMORY_ATTRIBUTE_EXECUTE           (1ULL << 2)
+  #define KVM_MEMORY_ATTRIBUTE_PRIVATE           (1ULL << 3)
+
+4.139 KVM_SET_MEMORY_ATTRIBUTES
+-----------------------------------------
+
+:Capability: KVM_CAP_MEMORY_ATTRIBUTES
+:Architectures: x86
+:Type: vm ioctl
+:Parameters: struct kvm_memory_attributes(in/out)
+:Returns: 0 on success, <0 on error
+
+Sets memory attributes for pages in a guest memory range. Parameters are
+specified via the following structure::
+
+  struct kvm_memory_attributes {
+       __u64 address;
+       __u64 size;
+       __u64 attributes;
+       __u64 flags;
+  };
+
+The user sets the per-page memory attributes to a guest memory range indicated
+by address/size, and in return KVM adjusts address and size to reflect the
+actual pages of the memory range have been successfully set to the attributes.
+If the call returns 0, "address" is updated to the last successful address + 1
+and "size" is updated to the remaining address size that has not been set
+successfully. The user should check the return value as well as the size to
+decide if the operation succeeded for the whole range or not. The user may want
+to retry the operation with the returned address/size if the previous range was
+partially successful.
+
+Both address and size should be page aligned and the supported attributes can 
be
+retrieved with KVM_GET_SUPPORTED_MEMORY_ATTRIBUTES.
+
+The "flags" field may be used for future extensions and should be set to 0s.
+
 5. The kvm_run structure
 ========================
 
@@ -8270,6 +8323,16 @@ structure.
 When getting the Modified Change Topology Report value, the attr->addr
 must point to a byte where the value will be stored or retrieved from.
 
+8.40 KVM_CAP_MEMORY_ATTRIBUTES
+------------------------------
+
+:Capability: KVM_CAP_MEMORY_ATTRIBUTES
+:Architectures: x86
+:Type: vm
+
+This capability indicates KVM supports per-page memory attributes and ioctls
+KVM_GET_SUPPORTED_MEMORY_ATTRIBUTES/KVM_SET_MEMORY_ATTRIBUTES are available.
+
 9. Known KVM API problems
 =========================
 
diff --git a/arch/x86/kvm/Kconfig b/arch/x86/kvm/Kconfig
index fbeaa9ddef59..a8e379a3afee 100644
--- a/arch/x86/kvm/Kconfig
+++ b/arch/x86/kvm/Kconfig
@@ -49,6 +49,7 @@ config KVM
        select SRCU
        select INTERVAL_TREE
        select HAVE_KVM_PM_NOTIFIER if PM
+       select HAVE_KVM_MEMORY_ATTRIBUTES
        help
          Support hosting fully virtualized guest machines using hardware
          virtualization extensions.  You will need a fairly recent
diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index 8f874a964313..a784e2b06625 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -800,6 +800,9 @@ struct kvm {
 
 #ifdef CONFIG_HAVE_KVM_PM_NOTIFIER
        struct notifier_block pm_notifier;
+#endif
+#ifdef CONFIG_HAVE_KVM_MEMORY_ATTRIBUTES
+       struct xarray mem_attr_array;
 #endif
        char stats_id[KVM_STATS_NAME_SIZE];
 };
diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
index 64dfe9c07c87..5d0941acb5bb 100644
--- a/include/uapi/linux/kvm.h
+++ b/include/uapi/linux/kvm.h
@@ -1182,6 +1182,7 @@ struct kvm_ppc_resize_hpt {
 #define KVM_CAP_S390_CPU_TOPOLOGY 222
 #define KVM_CAP_DIRTY_LOG_RING_ACQ_REL 223
 #define KVM_CAP_S390_PROTECTED_ASYNC_DISABLE 224
+#define KVM_CAP_MEMORY_ATTRIBUTES 225
 
 #ifdef KVM_CAP_IRQ_ROUTING
 
@@ -2238,4 +2239,20 @@ struct kvm_s390_zpci_op {
 /* flags for kvm_s390_zpci_op->u.reg_aen.flags */
 #define KVM_S390_ZPCIOP_REGAEN_HOST    (1 << 0)
 
+/* Available with KVM_CAP_MEMORY_ATTRIBUTES */
+#define KVM_GET_SUPPORTED_MEMORY_ATTRIBUTES    _IOR(KVMIO,  0xd2, __u64)
+#define KVM_SET_MEMORY_ATTRIBUTES              _IOWR(KVMIO,  0xd3, struct 
kvm_memory_attributes)
+
+struct kvm_memory_attributes {
+       __u64 address;
+       __u64 size;
+       __u64 attributes;
+       __u64 flags;
+};
+
+#define KVM_MEMORY_ATTRIBUTE_READ              (1ULL << 0)
+#define KVM_MEMORY_ATTRIBUTE_WRITE             (1ULL << 1)
+#define KVM_MEMORY_ATTRIBUTE_EXECUTE           (1ULL << 2)
+#define KVM_MEMORY_ATTRIBUTE_PRIVATE           (1ULL << 3)
+
 #endif /* __LINUX_KVM_H */
diff --git a/virt/kvm/Kconfig b/virt/kvm/Kconfig
index 800f9470e36b..effdea5dd4f0 100644
--- a/virt/kvm/Kconfig
+++ b/virt/kvm/Kconfig
@@ -19,6 +19,9 @@ config HAVE_KVM_IRQ_ROUTING
 config HAVE_KVM_DIRTY_RING
        bool
 
+config HAVE_KVM_MEMORY_ATTRIBUTES
+       bool
+
 # Only strongly ordered architectures can select this, as it doesn't
 # put any explicit constraint on userspace ordering. They can also
 # select the _ACQ_REL version.
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 1782c4555d94..7f0f5e9f2406 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -1150,6 +1150,9 @@ static struct kvm *kvm_create_vm(unsigned long type, 
const char *fdname)
        spin_lock_init(&kvm->mn_invalidate_lock);
        rcuwait_init(&kvm->mn_memslots_update_rcuwait);
        xa_init(&kvm->vcpu_array);
+#ifdef CONFIG_HAVE_KVM_MEMORY_ATTRIBUTES
+       xa_init(&kvm->mem_attr_array);
+#endif
 
        INIT_LIST_HEAD(&kvm->gpc_list);
        spin_lock_init(&kvm->gpc_lock);
@@ -1323,6 +1326,9 @@ static void kvm_destroy_vm(struct kvm *kvm)
                kvm_free_memslots(kvm, &kvm->__memslots[i][0]);
                kvm_free_memslots(kvm, &kvm->__memslots[i][1]);
        }
+#ifdef CONFIG_HAVE_KVM_MEMORY_ATTRIBUTES
+       xa_destroy(&kvm->mem_attr_array);
+#endif
        cleanup_srcu_struct(&kvm->irq_srcu);
        cleanup_srcu_struct(&kvm->srcu);
        kvm_arch_free_vm(kvm);
@@ -2323,6 +2329,49 @@ static int kvm_vm_ioctl_clear_dirty_log(struct kvm *kvm,
 }
 #endif /* CONFIG_KVM_GENERIC_DIRTYLOG_READ_PROTECT */
 
+#ifdef CONFIG_HAVE_KVM_MEMORY_ATTRIBUTES
+static u64 kvm_supported_mem_attributes(struct kvm *kvm)
+{
+       return 0;
+}
+
+static int kvm_vm_ioctl_set_mem_attributes(struct kvm *kvm,
+                                          struct kvm_memory_attributes *attrs)
+{
+       gfn_t start, end;
+       unsigned long i;
+       void *entry;
+       u64 supported_attrs = kvm_supported_mem_attributes(kvm);
+
+       /* flags is currently not used. */
+       if (attrs->flags)
+               return -EINVAL;
+       if (attrs->attributes & ~supported_attrs)
+               return -EINVAL;
+       if (attrs->size == 0 || attrs->address + attrs->size < attrs->address)
+               return -EINVAL;
+       if (!PAGE_ALIGNED(attrs->address) || !PAGE_ALIGNED(attrs->size))
+               return -EINVAL;
+
+       start = attrs->address >> PAGE_SHIFT;
+       end = (attrs->address + attrs->size - 1 + PAGE_SIZE) >> PAGE_SHIFT;
+
+       entry = attrs->attributes ? xa_mk_value(attrs->attributes) : NULL;
+
+       mutex_lock(&kvm->lock);
+       for (i = start; i < end; i++)
+               if (xa_err(xa_store(&kvm->mem_attr_array, i, entry,
+                                   GFP_KERNEL_ACCOUNT)))
+                       break;
+       mutex_unlock(&kvm->lock);
+
+       attrs->address = i << PAGE_SHIFT;
+       attrs->size = (end - i) << PAGE_SHIFT;
+
+       return 0;
+}
+#endif /* CONFIG_HAVE_KVM_MEMORY_ATTRIBUTES */
+
 struct kvm_memory_slot *gfn_to_memslot(struct kvm *kvm, gfn_t gfn)
 {
        return __gfn_to_memslot(kvm_memslots(kvm), gfn);
@@ -4459,6 +4508,9 @@ static long kvm_vm_ioctl_check_extension_generic(struct 
kvm *kvm, long arg)
 #ifdef CONFIG_HAVE_KVM_MSI
        case KVM_CAP_SIGNAL_MSI:
 #endif
+#ifdef CONFIG_HAVE_KVM_MEMORY_ATTRIBUTES
+       case KVM_CAP_MEMORY_ATTRIBUTES:
+#endif
 #ifdef CONFIG_HAVE_KVM_IRQFD
        case KVM_CAP_IRQFD:
        case KVM_CAP_IRQFD_RESAMPLE:
@@ -4804,6 +4856,30 @@ static long kvm_vm_ioctl(struct file *filp,
                break;
        }
 #endif /* CONFIG_HAVE_KVM_IRQ_ROUTING */
+#ifdef CONFIG_HAVE_KVM_MEMORY_ATTRIBUTES
+       case KVM_GET_SUPPORTED_MEMORY_ATTRIBUTES: {
+               u64 attrs = kvm_supported_mem_attributes(kvm);
+
+               r = -EFAULT;
+               if (copy_to_user(argp, &attrs, sizeof(attrs)))
+                       goto out;
+               r = 0;
+               break;
+       }
+       case KVM_SET_MEMORY_ATTRIBUTES: {
+               struct kvm_memory_attributes attrs;
+
+               r = -EFAULT;
+               if (copy_from_user(&attrs, argp, sizeof(attrs)))
+                       goto out;
+
+               r = kvm_vm_ioctl_set_mem_attributes(kvm, &attrs);
+
+               if (!r && copy_to_user(argp, &attrs, sizeof(attrs)))
+                       r = -EFAULT;
+               break;
+       }
+#endif /* CONFIG_HAVE_KVM_MEMORY_ATTRIBUTES */
        case KVM_CREATE_DEVICE: {
                struct kvm_create_device cd;
 
-- 
2.25.1