Explain steps to enable the dynamic feature with a code example.
Signed-off-by: Chang S. Bae <chang.seok.bae@xxxxxxxxx>
Reviewed-by: Thiago Macieira <thiago.macieira@xxxxxxxxx>
Cc: Dave Hansen <dave.hansen@xxxxxxxxx>
Cc: Bagas Sanjaya <bagasdotme@xxxxxxxxx>
Cc: linux-doc@xxxxxxxxxxxxxxx
Cc: linux-kernel@xxxxxxxxxxxxxxx
---
Changes from v1:
* Update the description without mentioning CPUID & XGETBV (Dave Hansen).
Changes from v2:
* Massage sentences (Bagas Sanjaya).
* Adjust the example with the (future) prctl.h.
---
Documentation/x86/xstate.rst | 55 ++++++++++++++++++++++++++++++++++++
1 file changed, 55 insertions(+)
diff --git a/Documentation/x86/xstate.rst b/Documentation/x86/xstate.rst
index 5cec7fb558d6..dbe7ca854d2a 100644
--- a/Documentation/x86/xstate.rst
+++ b/Documentation/x86/xstate.rst
@@ -64,6 +64,61 @@ 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
---------------------------------
--
2.17.1
