KVM: Don't pre-reserve xarray entries when storing empty/NULL attributesgrafted

Skip the xarray reservation loop when clearing all memory attributes, as
storing NULL only erases the entry and never needs to allocate, so no
reservation (and no cleanup of a failed one) is required in that case.

Suggested-by: Sean Christopherson <seanjc@google.com>
Cc: David Ballesteros <davimaba.v@proton.me>
Signed-off-by: Zeng Chi <zengchi@kylinos.cn>
Link: https://patch.msgid.link/20260921102442.1232375-1-zeng_chi911@163.com
[sean: split to separate patch]
Signed-off-by: Sean Christopherson <seanjc@google.com>

2 files changed, 151 insertions, 0 deletions

diff --git a/Documentation/driver-api/issei/index.rst b/Documentation/driver-api/issei/index.rst
new file mode 100644
index 000000000..604267463
--- /dev/null
+++ b/Documentation/driver-api/issei/index.rst
@@ -0,0 +1,16 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+.. include:: <isonum.txt>
+
+=========================================================
+The Intel Silicon Security Engine Interface (Intel SSEI)
+=========================================================
+
+**Copyright** |copy| 2026 Intel Corporation
+
+
+.. toctree::
+   :caption: Table of Contents
+   :maxdepth: 3
+
+   issei
diff --git a/Documentation/driver-api/issei/issei.rst b/Documentation/driver-api/issei/issei.rst
new file mode 100644
index 000000000..a5e99e92e
--- /dev/null
+++ b/Documentation/driver-api/issei/issei.rst
@@ -0,0 +1,135 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+Introduction
+============
+
+The Intel Silicon Security Engine (Intel SSE) is an isolated and
+protected computing resource (Co-processor) residing inside
+Intel client chipsets released in 2024 (Lunar Lake) or later.
+The Intel SSE provide security support and platform boot orchestration.
+The actual feature set depends on the Intel chipset SKU.
+
+The Intel Silicon Security Engine Interface (Intel SSEI)
+is the interface between the Host and Intel SSE.
+This interface is exposed to the host as one or more PCI devices.
+The Intel SSEI Driver is in charge of the communication channel between
+a host application and the Intel SSE features.
+
+Each Intel SSE feature, or Intel SSE Client is addressed by a unique UUID and
+each client has its own protocol. The protocol is message-based with a
+header and payload up to maximal number of bytes advertised by the client,
+upon connection.
+
+Intel SSEI Driver
+=================
+
+The driver exposes a character device with device nodes /dev/isseiX.
+
+An application maintains communication with an Intel SSE feature while
+/dev/isseiX is open. The binding to a specific feature is performed by calling
+:c:macro:`IOCTL_ISSEI_CONNECT_CLIENT`, which passes the desired UUID.
+The number of instances of an Intel SSE feature that can be opened
+at the same time is limited to single instance.
+
+The driver is transparent to data that are passed between firmware feature
+and host application.
+
+Because some of the Intel SSE features can change the system
+configuration, the driver by default allows only a privileged
+user to access it.
+
+The connection termination is performed by calling
+:c:macro:`IOCTL_ISSEI_DISCONNECT_CLIENT`.
+
+The session is terminated calling :c:expr:`close(fd)`.
+
+A code snippet for an application communicating with SPDM client:
+
+.. code-block:: C
+
+        struct issei_connect_client_data data = {.in_client_uuid =
+                {0xe8, 0x51, 0x49, 0xdf, 0x94, 0x47, 0x4C,
+                 0x9A, 0x83, 0x67, 0xC4, 0xE3, 0x34, 0x64, 0xF1, 0xB4}};
+        __u8 req_data[] = {0x10, 0x84, 0x00, 0x00}; /* SPDM Get Version */
+        size_t req_data_len = sizeof(req_data);
+        __u8 res_data[256];
+        size_t res_data_len = sizeof(res_data);
+        int fd = open("/dev/issei0", O_RDWR);
+
+        ioctl(fd, IOCTL_ISSEI_CONNECT_CLIENT, &data);
+
+        printf("Ver=%d, MaxLen=%u, Flags=0x%08X\n",
+               data.out_client_properties.protocol_version,
+               data.out_client_properties.max_msg_length,
+               data.out_client_properties.flags);
+
+        [...]
+
+        write(fd, req_data, req_data_len);
+
+        [...]
+
+        read(fd, res_data, res_data_len);
+
+        printf("SPDM version count %u, version[0]=%02X%02X\n",
+               res_data[5], res_data[6], res_data[7]);
+
+        [...]
+
+        ioctl(fd, IOCTL_ISSEI_DISCONNECT_CLIENT, &data);
+
+        [...]
+
+        close(fd);
+
+
+User space API ioctl
+====================
+
+The Intel SSEI Driver supports the following ioctl commands:
+
+IOCTL_ISSEI_CONNECT_CLIENT
+--------------------------
+Connect to firmware Feature/Client.
+
+.. code-block:: none
+
+        Usage:
+
+        struct issei_connect_client_data client_data;
+
+        ioctl(fd, IOCTL_ISSEI_CONNECT_CLIENT, &client_data);
+
+        struct issei_connect_client_data - contain the following
+        Inputs:
+                in_client_uuid        - UUID of the FW Feature that needs to connect to.
+        Outputs:
+                out_client_properties - Client Properties: MTU, Protocol Version and Flags.
+
+        Error returns:
+                ENOTTY  No such client (i.e. wrong UUID) or connection is not allowed.
+                EINVAL  Wrong IOCTL Number
+                ENODEV  Device or Connection is not initialized or ready.
+                ENOMEM  Unable to allocate memory to client internal data.
+                EFAULT  Fatal Error (e.g. Unable to access user input data)
+                EBUSY   Connection Already Open
+
+:Note:
+        max_msg_length (MTU) in client properties describes the maximum
+        data that can be sent or received. (e.g. with MTU=2K, can send
+        requests up to bytes 2k and received responses up to 2k bytes).
+
+IOCTL_ISSEI_DISCONNECT_CLIENT
+-----------------------------
+Disconnect from firmware Feature/Client.
+
+.. code-block:: none
+
+        Usage:
+
+        ioctl(fd, IOCTL_ISSEI_DISCONNECT_CLIENT, NULL);
+
+        Error returns:
+                EINVAL    Wrong IOCTL Number
+                ENODEV    Device or Connection is not initialized or ready.
+                ENOTCONN  Feature/Client is not connected.