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From: Dave Hansen <dave.hansen@intel.com>
To: "Brown, Len" <len.brown@intel.com>,
	Andy Lutomirski <luto@kernel.org>,
	"Bae, Chang Seok" <chang.seok.bae@intel.com>
Cc: Thomas Gleixner <tglx@linutronix.de>,
	Ingo Molnar <mingo@kernel.org>, Borislav Petkov <bp@suse.de>,
	X86 ML <x86@kernel.org>, "Liu, Jing2" <jing2.liu@intel.com>,
	"Shankar, Ravi V" <ravi.v.shankar@intel.com>,
	LKML <linux-kernel@vger.kernel.org>
Subject: Re: [RFC PATCH 13/22] x86/fpu/xstate: Expand dynamic user state area on first use
Date: Tue, 13 Oct 2020 15:43:59 -0700	[thread overview]
Message-ID: <c4669d5f-11b8-3879-562c-78a791b86229@intel.com> (raw)
In-Reply-To: <BYAPR11MB346371298609756EFD2DDA1EE0040@BYAPR11MB3463.namprd11.prod.outlook.com>

On 10/13/20 3:31 PM, Brown, Len wrote:
> vmalloc() does not fail, and does not return an error, and so there is no concept
> of returning a signal.

Well, the order-0 allocations are no-fail, as are the vmalloc kernel
structures and the page tables that might have to be allocated.  But,
that's not guaranteed to be in place *forever*.  I think we still need
to check for and handle allocation failures, even if they're not known
to be possible today.

> If we got to the point where vmalloc() sleeps, then the system
> has bigger OOM issues, and the OOM killer would be on the prowl.

vmalloc() can *certainly* sleep.  Allocation failures mean returning
NULL from the allocator, and the very way we avoid doing that is by
sleeping to go reclaim some memory from some other allocation.

Sleeping is a normal and healthy part of handling allocation requests,
including vmalloc().

> If we were concerned about using vmalloc for a couple of pages in the task structure,
> Then we could implement a routine to harvest unused buffers and free them --
> but that didn't seem worth the complexity.  Note that this feature is 64-bit only.

IMNHO, vmalloc() is overkill for ~10k, which is roughly the size of the
XSAVE buffer for the first AMX implementation.  But, it's not overkill
for the ~66k of space that will be needed if some CPU implementation
comes along and uses all of the architectural space AMX provides.

  reply	other threads:[~2020-10-13 22:44 UTC|newest]

Thread overview: 43+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-10-01 20:38 [RFC PATCH 00/22] x86: Support Intel Advanced Matrix Extensions Chang S. Bae
2020-10-01 20:38 ` [RFC PATCH 01/22] x86/fpu/xstate: Modify area init helper prototypes to access all the possible areas Chang S. Bae
2020-10-01 20:38 ` [RFC PATCH 02/22] x86/fpu/xstate: Modify xstate copy " Chang S. Bae
2020-10-01 20:38 ` [RFC PATCH 03/22] x86/fpu/xstate: Modify address finder " Chang S. Bae
2020-10-01 20:38 ` [RFC PATCH 04/22] x86/fpu/xstate: Modify save and restore helper " Chang S. Bae
2020-10-01 20:38 ` [RFC PATCH 05/22] x86/fpu/xstate: Introduce a new variable for dynamic user states Chang S. Bae
2020-10-01 20:38 ` [RFC PATCH 06/22] x86/fpu/xstate: Outline dynamic xstate area size in the task context Chang S. Bae
2020-10-01 20:38 ` [RFC PATCH 07/22] x86/fpu/xstate: Introduce helpers to manage an xstate area dynamically Chang S. Bae
2020-10-01 23:41   ` Andy Lutomirski
2020-10-13 22:00     ` Brown, Len
2020-10-01 20:38 ` [RFC PATCH 08/22] x86/fpu/xstate: Define the scope of the initial xstate data Chang S. Bae
2020-10-01 20:39 ` [RFC PATCH 09/22] x86/fpu/xstate: Introduce wrapper functions for organizing xstate area access Chang S. Bae
2020-10-01 20:39 ` [RFC PATCH 10/22] x86/fpu/xstate: Update xstate save function for supporting dynamic user xstate Chang S. Bae
2020-10-01 20:39 ` [RFC PATCH 11/22] x86/fpu/xstate: Update xstate area address finder " Chang S. Bae
2020-10-01 20:39 ` [RFC PATCH 12/22] x86/fpu/xstate: Update xstate context copy function for supporting dynamic area Chang S. Bae
2020-10-01 20:39 ` [RFC PATCH 13/22] x86/fpu/xstate: Expand dynamic user state area on first use Chang S. Bae
2020-10-01 23:39   ` Andy Lutomirski
2020-10-13 22:31     ` Brown, Len
2020-10-13 22:43       ` Dave Hansen [this message]
2020-10-14  1:11         ` Andy Lutomirski
2020-10-14  6:03           ` Dave Hansen
2020-10-14 16:10             ` Andy Lutomirski
2020-10-14 16:29               ` Dave Hansen
2020-11-03 21:32                 ` Bae, Chang Seok
2020-11-03 21:41                   ` Dave Hansen
2020-11-03 21:53                     ` Bae, Chang Seok
2020-10-14 10:41         ` Peter Zijlstra
2020-10-14  1:47       ` Andy Lutomirski
2020-10-01 20:39 ` [RFC PATCH 14/22] x86/fpu/xstate: Inherit dynamic user state when used in the parent Chang S. Bae
2020-10-01 20:39 ` [RFC PATCH 15/22] x86/fpu/xstate: Support ptracer-induced xstate area expansion Chang S. Bae
2020-10-01 20:39 ` [RFC PATCH 16/22] x86/fpu/xstate: Support dynamic user state in the signal handling path Chang S. Bae
2020-10-01 20:39 ` [RFC PATCH 17/22] x86/fpu/xstate: Extend the table for mapping xstate components with features Chang S. Bae
2020-10-01 20:39 ` [RFC PATCH 18/22] x86/cpufeatures/amx: Enumerate Advanced Matrix Extension (AMX) feature bits Chang S. Bae
2020-10-01 20:39 ` [RFC PATCH 19/22] x86/fpu/amx: Define AMX state components and have it used for boot-time checks Chang S. Bae
2020-10-01 20:39 ` [RFC PATCH 20/22] x86/fpu/amx: Enable the AMX feature in 64-bit mode Chang S. Bae
2020-10-01 20:39 ` [RFC PATCH 21/22] selftest/x86/amx: Include test cases for the AMX state management Chang S. Bae
2020-10-01 20:39 ` [RFC PATCH 22/22] x86/fpu/xstate: Introduce boot-parameters for control some state component support Chang S. Bae
2020-10-02  2:09   ` Randy Dunlap
2020-10-13 23:00     ` Brown, Len
2020-10-02 17:15   ` Andy Lutomirski
2020-10-02 17:26     ` Dave Hansen
2020-10-13 23:38     ` Brown, Len
2020-10-02 17:25   ` Dave Hansen

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