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