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

From: Binbin Wu
Date: Mon Jan 16 2023 - 22:21:41 EST


On 12/2/2022 2:13 PM, Chao Peng wrote:
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@xxxxxxxxxx>
Signed-off-by: Chao Peng <chao.p.peng@xxxxxxxxxxxxxxx>
Link: https://lore.kernel.org/all/Y2WB48kD0J4VGynX@xxxxxxxxxx/
---
Documentation/virt/kvm/api.rst | 63 ++++++++++++++++++++++++++++
arch/x86/kvm/Kconfig | 1 +
include/linux/kvm_host.h | 3 ++
include/uapi/linux/kvm.h | 17 ++++++++

Should the changes introduced in this file also need to be added in tools/include/uapi/linux/kvm.h ?



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;