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@xxxxxxxxx>
AuthorDate: Fri, 20 Jan 2023 16:18:59 -08:00
Committer: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
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@xxxxxxxxx>
Signed-off-by: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
Reviewed-by: Thiago Macieira <thiago.macieira@xxxxxxxxx>
Reviewed-by: Bagas Sanjaya <bagasdotme@xxxxxxxxx>
Reviewed-by: Tony Luck <tony.luck@xxxxxxxxx>
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
---------------------------------
|