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Documentation/x86: Add the AMX enabling example

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

Signed-off-by: Chang S. Bae <chang.seok.bae@intel.com>
Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
Reviewed-by: Bagas Sanjaya <bagasdotme@gmail.com>
Reviewed-by: Tony Luck <tony.luck@intel.com>
Link: https://lore.kernel.org/all/20230121001900.14900-4-chang.seok.bae%40intel.com
This commit is contained in:
Chang S. Bae 2023-01-20 16:18:59 -08:00 committed by Dave Hansen
parent a03c376eba
commit 7f9daaf59e
1 changed files with 55 additions and 0 deletions
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55
Documentation/x86/xstate.rst
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@ -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
---------------------------------