From: Len Brown <lenb@kernel.org>
To: Andy Lutomirski <luto@kernel.org>
Cc: "Chang S. Bae" <chang.seok.bae@intel.com>,
Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@kernel.org>, Borislav Petkov <bp@suse.de>,
X86 ML <x86@kernel.org>, Len Brown <len.brown@intel.com>,
Dave Hansen <dave.hansen@intel.com>,
"Liu, Jing2" <jing2.liu@intel.com>,
"Ravi V. Shankar" <ravi.v.shankar@intel.com>,
LKML <linux-kernel@vger.kernel.org>,
"open list:DOCUMENTATION" <linux-doc@vger.kernel.org>
Subject: Re: [PATCH v2 22/22] x86/fpu/xstate: Introduce boot-parameters for control some state component support
Date: Tue, 24 Nov 2020 13:50:58 -0500 [thread overview]
Message-ID: <CAJvTdKng_WMrmO_KtkuCxvvzGZ_HLcd84u2SwJiD_UJivb4Yaw@mail.gmail.com> (raw)
In-Reply-To: <CALCETrXBRATBVySDM9f0H-+gD37n7=CsNLWa446eLHi1mjokGw@mail.gmail.com>
On Fri, Nov 20, 2020 at 12:03 AM Andy Lutomirski <luto@kernel.org> wrote:
>
> On Thu, Nov 19, 2020 at 3:37 PM Chang S. Bae <chang.seok.bae@intel.com> wrote:
> > "xstate.enable=0x60000" will enable AMX on a system that does NOT have AMX
> > compiled into XFEATURE_MASK_USER_ENABLED (assuming the kernel is new enough
> > to support this feature).
> >
>
> What's the purpose of xstate.enable? I can't really imagine it's
> useful for AMX. I suppose it could be useful for hypothetical
> post-AMX features, but that sounds extremely dangerous. Intel has
> changed its strategy so many times on XSTATE extensibility that I find
> it quite hard to believe that supporting unknown states is wise.
Not hypothetical -- there are subsequent hardware features coming that
will use the same
exact XSTATE support that this series puts in place for AMX.
We know that when those features ship in new hardware, there will be
a set of customers who want to exercise those features immediately,
but their kernel binary has not yet been re-compiled to see those
features by-default.
The purpose of "xstate.enable" is to empower those users to be able to
explicitly enable support using their existing binary.
You are right -- the feature isn't needed to enable AMX, unless somebody went to
the trouble of building a kernel with the AMX source update, but chose
to disable
AMX-specific recognition, by-default.
thanks,
Len Brown, Intel Open Source Technology Center
next prev parent reply other threads:[~2020-11-24 18:51 UTC|newest]
Thread overview: 38+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-11-19 23:32 [PATCH v2 00/22] x86: Support Intel Advanced Matrix Extensions Chang S. Bae
2020-11-19 23:32 ` [PATCH v2 01/22] x86/fpu/xstate: Modify area init helper prototypes to access all the possible areas Chang S. Bae
2020-12-07 17:12 ` Borislav Petkov
2020-12-07 23:03 ` Bae, Chang Seok
2020-12-07 23:10 ` Borislav Petkov
2020-11-19 23:32 ` [PATCH v2 02/22] x86/fpu/xstate: Modify xstate copy " Chang S. Bae
2020-11-19 23:32 ` [PATCH v2 03/22] x86/fpu/xstate: Modify address finder " Chang S. Bae
2020-11-19 23:32 ` [PATCH v2 04/22] x86/fpu/xstate: Modify save and restore helper " Chang S. Bae
2020-11-19 23:32 ` [PATCH v2 05/22] x86/fpu/xstate: Introduce a new variable for dynamic user states Chang S. Bae
2020-11-19 23:32 ` [PATCH v2 06/22] x86/fpu/xstate: Outline dynamic xstate area size in the task context Chang S. Bae
2020-11-19 23:32 ` [PATCH v2 07/22] x86/fpu/xstate: Introduce helpers to manage an xstate area dynamically Chang S. Bae
2020-11-19 23:32 ` [PATCH v2 08/22] x86/fpu/xstate: Define the scope of the initial xstate data Chang S. Bae
2020-11-19 23:32 ` [PATCH v2 09/22] x86/fpu/xstate: Introduce wrapper functions for organizing xstate area access Chang S. Bae
2020-11-19 23:32 ` [PATCH v2 10/22] x86/fpu/xstate: Update xstate save function for supporting dynamic user xstate Chang S. Bae
2020-11-19 23:32 ` [PATCH v2 11/22] x86/fpu/xstate: Update xstate area address finder " Chang S. Bae
2020-11-19 23:32 ` [PATCH v2 12/22] x86/fpu/xstate: Update xstate context copy function for supporting dynamic area Chang S. Bae
2020-11-19 23:32 ` [PATCH v2 13/22] x86/fpu/xstate: Expand dynamic user state area on first use Chang S. Bae
2020-11-19 23:32 ` [PATCH v2 14/22] x86/fpu/xstate: Inherit dynamic user state when used in the parent Chang S. Bae
2020-11-20 5:08 ` Andy Lutomirski
2020-11-24 18:35 ` Len Brown
2020-11-19 23:32 ` [PATCH v2 15/22] x86/fpu/xstate: Support ptracer-induced xstate area expansion Chang S. Bae
2020-11-20 5:07 ` Andy Lutomirski
2020-11-24 18:22 ` Bae, Chang Seok
2020-11-24 18:33 ` Andy Lutomirski
2020-12-02 4:00 ` Bae, Chang Seok
2020-12-03 5:00 ` Andy Lutomirski
2020-12-08 19:12 ` Bae, Chang Seok
2020-11-19 23:32 ` [PATCH v2 16/22] x86/fpu/xstate: Extend the table for mapping xstate components with features Chang S. Bae
2020-11-19 23:32 ` [PATCH v2 17/22] x86/cpufeatures/amx: Enumerate Advanced Matrix Extension (AMX) feature bits Chang S. Bae
2020-11-19 23:32 ` [PATCH v2 18/22] x86/fpu/amx: Define AMX state components and have it used for boot-time checks Chang S. Bae
2020-11-19 23:32 ` [PATCH v2 19/22] x86/fpu/amx: Enable the AMX feature in 64-bit mode Chang S. Bae
2020-11-19 23:32 ` [PATCH v2 20/22] selftest/x86/amx: Include test cases for the AMX state management Chang S. Bae
2020-11-19 23:32 ` [PATCH v2 21/22] x86/fpu/xstate: Support dynamic user state in the signal handling path Chang S. Bae
2020-11-19 23:32 ` [PATCH v2 22/22] x86/fpu/xstate: Introduce boot-parameters for control some state component support Chang S. Bae
2020-11-20 5:02 ` Andy Lutomirski
2020-11-24 18:50 ` Len Brown [this message]
2020-11-24 23:41 ` Andy Lutomirski
2020-12-01 18:00 ` Len Brown
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