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Date: Wed, 29 Jun 2022 15:42:35 -0700 From: "Chang S. Bae" <chang.seok.bae@...el.com> To: dave.hansen@...el.com, len.brown@...el.com, tony.luck@...el.com, rafael.j.wysocki@...el.com, reinette.chatre@...el.com, dan.j.williams@...el.com Cc: corbet@....net, linux-doc@...r.kernel.org, linux-man@...r.kernel.org, linux-kernel@...r.kernel.org, chang.seok.bae@...el.com Subject: [PATCH v2 1/1] 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> Reviewed-by: Thiago Macieira <thiago.macieira@...el.com> Cc: linux-doc@...r.kernel.org Cc: linux-kernel@...r.kernel.org --- Changes from v1: * Update the description without mentioning CPUID & XGETBV (Dave Hansen). --- Documentation/x86/xstate.rst | 42 ++++++++++++++++++++++++++++++++++++ 1 file changed, 42 insertions(+) diff --git a/Documentation/x86/xstate.rst b/Documentation/x86/xstate.rst index 5cec7fb558d6..c439901419fb 100644 --- a/Documentation/x86/xstate.rst +++ b/Documentation/x86/xstate.rst @@ -64,6 +64,48 @@ 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 +^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ + +The following steps dynamically enable TILE_DATA: + + 1. An application first needs to determine the feature support:: + + #include <asm/prctl.h> + #include <sys/syscall.h> + #include <stdio.h> + #include <unistd.h> + + #define ARCH_GET_XCOMP_SUPP 0x1021 + + #define XFEATURE_XTILECFG 17 + #define XFEATURE_XTILEDATA 18 + #define XFEATURE_MASK_XTILE ((1 << XFEATURE_XTILECFG) | (1 << XFEATURE_XTILEDATA)) + + unsigned long features; + long rc; + + ... + + rc = syscall(SYS_arch_prctl, ARCH_GET_XCOMP_SUPP, &features); + + if (!rc && (features & XFEATURE_MASK_XTILE) == XFEATURE_MASK_XTILE) + printf("AMX is available.\n"); + + 2. After determining support for AMX, an application must explicitly ask + permission to use it:: + + #define ARCH_REQ_XCOMP_PERM 0x1023 + + ... + + rc = syscall(SYS_arch_prctl, ARCH_REQ_XCOMP_PERM, XFEATURE_XTILEDATA); + + 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
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