linux-kernel - [tip: x86/fpu] Documentation/x86: Add the AMX enabling example

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Date:   Wed, 22 Mar 2023 20:14:53 -0000
From:   "tip-bot2 for Chang S. Bae" <tip-bot2@...utronix.de>
To:     linux-tip-commits@...r.kernel.org
Cc:     "Chang S. Bae" <chang.seok.bae@...el.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Thiago Macieira <thiago.macieira@...el.com>,
        Bagas Sanjaya <bagasdotme@...il.com>,
        Tony Luck <tony.luck@...el.com>, x86@...nel.org,
        linux-kernel@...r.kernel.org
Subject: [tip: x86/fpu] Documentation/x86: Add the AMX enabling example

The following commit has been merged into the x86/fpu branch of tip:

Commit-ID:     7f9daaf59e14d62b29b6f4ca743e17bf96ff42ae
Gitweb:        https://git.kernel.org/tip/7f9daaf59e14d62b29b6f4ca743e17bf96ff42ae
Author:        Chang S. Bae <chang.seok.bae@...el.com>
AuthorDate:    Fri, 20 Jan 2023 16:18:59 -08:00
Committer:     Dave Hansen <dave.hansen@...ux.intel.com>
CommitterDate: Wed, 22 Mar 2023 13:07:58 -07:00

Documentation/x86: Add the AMX enabling example

Explain steps to enable the dynamic feature with a code example.

Signed-off-by: Chang S. Bae <chang.seok.bae@...el.com>
Signed-off-by: Dave Hansen <dave.hansen@...ux.intel.com>
Reviewed-by: Thiago Macieira <thiago.macieira@...el.com>
Reviewed-by: Bagas Sanjaya <bagasdotme@...il.com>
Reviewed-by: Tony Luck <tony.luck@...el.com>
Link: https://lore.kernel.org/all/20230121001900.14900-4-chang.seok.bae%40intel.com
---
 Documentation/x86/xstate.rst | 55 +++++++++++++++++++++++++++++++++++-
 1 file changed, 55 insertions(+)

diff --git a/Documentation/x86/xstate.rst b/Documentation/x86/xstate.rst
index e954e79..23b1c9f 100644
--- a/Documentation/x86/xstate.rst
+++ b/Documentation/x86/xstate.rst
@@ -80,6 +80,61 @@ the handler allocates a larger xstate buffer for the task so the large
 state can be context switched. In the unlikely cases that the allocation
 fails, the kernel sends SIGSEGV.
 
+AMX TILE_DATA enabling example
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Below is the example of how userspace applications enable
+TILE_DATA dynamically:
+
+  1. The application first needs to query the kernel for AMX
+     support::
+
+        #include <asm/prctl.h>
+        #include <sys/syscall.h>
+        #include <stdio.h>
+        #include <unistd.h>
+
+        #ifndef ARCH_GET_XCOMP_SUPP
+        #define ARCH_GET_XCOMP_SUPP  0x1021
+        #endif
+
+        #ifndef ARCH_XCOMP_TILECFG
+        #define ARCH_XCOMP_TILECFG   17
+        #endif
+
+        #ifndef ARCH_XCOMP_TILEDATA
+        #define ARCH_XCOMP_TILEDATA  18
+        #endif
+
+        #define MASK_XCOMP_TILE      ((1 << ARCH_XCOMP_TILECFG) | \
+                                      (1 << ARCH_XCOMP_TILEDATA))
+
+        unsigned long features;
+        long rc;
+
+        ...
+
+        rc = syscall(SYS_arch_prctl, ARCH_GET_XCOMP_SUPP, &features);
+
+        if (!rc && (features & MASK_XCOMP_TILE) == MASK_XCOMP_TILE)
+            printf("AMX is available.\n");
+
+  2. After that, determining support for AMX, an application must
+     explicitly ask permission to use it::
+
+        #ifndef ARCH_REQ_XCOMP_PERM
+        #define ARCH_REQ_XCOMP_PERM  0x1023
+        #endif
+
+        ...
+
+        rc = syscall(SYS_arch_prctl, ARCH_REQ_XCOMP_PERM, ARCH_XCOMP_TILEDATA);
+
+        if (!rc)
+            printf("AMX is ready for use.\n");
+
+Note this example does not include the sigaltstack preparation.
+
 Dynamic features in signal frames
 ---------------------------------