Commit 7f9daaf5 authored by Chang S. Bae's avatar Chang S. Bae Committed by Dave Hansen
Browse files

Documentation/x86: Add the AMX enabling example 



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

Signed-off-by: default avatarChang S. Bae <chang.seok.bae@intel.com>
Signed-off-by: default avatarDave Hansen <dave.hansen@linux.intel.com>
Reviewed-by: default avatarThiago Macieira <thiago.macieira@intel.com>
Reviewed-by: default avatarBagas Sanjaya <bagasdotme@gmail.com>
Reviewed-by: default avatarTony Luck <tony.luck@intel.com>
Link: https://lore.kernel.org/all/20230121001900.14900-4-chang.seok.bae%40intel.com
parent a03c376e

Documentation/x86/xstate.rst

+55 −0
Original line number Diff line number Diff line
@@ -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

---------------------------------