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From: Dave Hansen <dave.hansen@intel.com>
To: Len Brown <lenb@kernel.org>, Borislav Petkov <bp@alien8.de>
Cc: "Chang S. Bae" <chang.seok.bae@intel.com>,
	Andy Lutomirski <luto@kernel.org>,
	Thomas Gleixner <tglx@linutronix.de>,
	Ingo Molnar <mingo@kernel.org>, X86 ML <x86@kernel.org>,
	"Brown, Len" <len.brown@intel.com>,
	thiago.macieira@intel.com, "Liu, Jing2" <jing2.liu@intel.com>,
	"Ravi V. Shankar" <ravi.v.shankar@intel.com>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH v9 12/26] x86/fpu/xstate: Use feature disable (XFD) to protect dynamic user state
Date: Mon, 30 Aug 2021 11:04:40 -0700	[thread overview]
Message-ID: <a96a65fc-061b-e94b-cee7-16201ac0820f@intel.com> (raw)
In-Reply-To: <CAJvTdKn09GiAOgdsOR-+ooEO=bmj8VDL9e9sSAsu2UPx73a-Mw@mail.gmail.com>

On 8/24/21 4:17 PM, Len Brown wrote:
> Even if your AMX thread pool threads were to invoke this system call
> as soon as possible...
> What is to say that the thread pool is created only at a time when memory
> is available?  A thread could be created 24 hours into program execution
> under OOM conditions and this system call will return ENOMEM, and your program
> will in all likelihood throw up its arms and exit at the exact same place
> it would exit for transparently allocated buffers.

I tried this exact line of reasoning with Thomas: it doesn't matter
where we run out of memory, we still need the same memory and we're
screwed either way.

However, Thomas expressed a clear preference for ABIs which return
memory failures explicitly at syscalls versus implicit failures which
can happen on random instructions.

One might say that the odds of checking for and handling a NULL value
(or ENOMEM) are the same as installing a signal handler.  *But*, it's
infinitely easier to unroll state and recover from a NULL than it is to
handle it from within a signal handler.  In other words, the explicit
ones *encourage* better programming.

I'd prefer removing the demand-driven allocation at this point.

  parent reply	other threads:[~2021-08-30 18:04 UTC|newest]

Thread overview: 91+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-07-30 14:59 [PATCH v9 00/26] x86: Support Intel Advanced Matrix Extensions Chang S. Bae
2021-07-30 14:59 ` [PATCH v9 01/26] x86/fpu/xstate: Modify the initialization helper to handle both static and dynamic buffers Chang S. Bae
2021-07-30 14:59 ` [PATCH v9 02/26] x86/fpu/xstate: Modify state copy helpers " Chang S. Bae
2021-07-30 14:59 ` [PATCH v9 03/26] x86/fpu/xstate: Modify address finders " Chang S. Bae
2021-07-30 14:59 ` [PATCH v9 04/26] x86/fpu/xstate: Add a new variable to indicate dynamic user states Chang S. Bae
2021-07-30 14:59 ` [PATCH v9 05/26] x86/fpu/xstate: Add new variables to indicate dynamic XSTATE buffer size Chang S. Bae
2021-08-12 15:03   ` Borislav Petkov
2021-07-30 14:59 ` [PATCH v9 06/26] x86/fpu/xstate: Calculate and remember dynamic XSTATE buffer sizes Chang S. Bae
2021-08-12 16:36   ` Borislav Petkov
2021-07-30 14:59 ` [PATCH v9 07/26] x86/fpu/xstate: Convert the struct fpu 'state' field to a pointer Chang S. Bae
2021-08-12 17:09   ` Borislav Petkov
2021-07-30 14:59 ` [PATCH v9 08/26] x86/fpu/xstate: Introduce helpers to manage the XSTATE buffer dynamically Chang S. Bae
2021-08-12 19:44   ` Borislav Petkov
2021-08-13  8:04     ` Bae, Chang Seok
2021-08-13 10:04       ` Borislav Petkov
2021-08-13 19:43         ` Bae, Chang Seok
2021-08-18  9:28           ` Borislav Petkov
2021-08-18 19:46             ` Bae, Chang Seok
2021-08-25 16:01               ` Bae, Chang Seok
2021-08-30 17:07               ` Borislav Petkov
2021-08-30 23:39                 ` Bae, Chang Seok
2021-08-16 18:33     ` Bae, Chang Seok
2021-08-16 18:53       ` Borislav Petkov
2021-08-30 17:45   ` Dave Hansen
2021-08-30 23:39     ` Bae, Chang Seok
2021-07-30 14:59 ` [PATCH v9 09/26] x86/fpu/xstate: Update the XSTATE save function to support dynamic states Chang S. Bae
2021-07-30 14:59 ` [PATCH v9 10/26] x86/fpu/xstate: Update the XSTATE buffer address finder " Chang S. Bae
2021-08-18 11:33   ` Borislav Petkov
2021-08-18 19:47     ` Bae, Chang Seok
2021-08-30 17:18       ` Borislav Petkov
2021-08-30 23:38         ` Bae, Chang Seok
2021-07-30 14:59 ` [PATCH v9 11/26] x86/fpu/xstate: Update the XSTATE context copy function " Chang S. Bae
2021-08-18 12:03   ` Borislav Petkov
2021-08-18 19:47     ` Bae, Chang Seok
2021-07-30 14:59 ` [PATCH v9 12/26] x86/fpu/xstate: Use feature disable (XFD) to protect dynamic user state Chang S. Bae
2021-08-18 16:24   ` Borislav Petkov
2021-08-18 17:20     ` Thiago Macieira
2021-08-18 17:46       ` Borislav Petkov
2021-08-18 17:58         ` Thiago Macieira
2021-08-18 18:10           ` Borislav Petkov
2021-08-24 22:51             ` Len Brown
2021-08-18 20:43         ` Bae, Chang Seok
2021-08-18 21:04           ` Thiago Macieira
2021-08-18 21:12             ` Bae, Chang Seok
2021-08-18 22:27               ` Thiago Macieira
2021-08-19  1:21             ` Andy Lutomirski
2021-08-19 16:06               ` Thiago Macieira
2021-08-18 21:17           ` Borislav Petkov
2021-08-18 21:37             ` Bae, Chang Seok
2021-08-19  8:00               ` Borislav Petkov
2021-08-19 15:24                 ` Bae, Chang Seok
2021-08-24 23:22             ` Len Brown
2021-08-30 17:31               ` Borislav Petkov
2021-09-17  3:48                 ` Len Brown
2021-08-18 19:47     ` Bae, Chang Seok
2021-08-24 22:21     ` Len Brown
2021-08-30 17:41       ` Borislav Petkov
2021-08-31 21:44         ` Len Brown
2021-08-24 23:17     ` Len Brown
2021-08-30 17:53       ` Borislav Petkov
2021-08-31 22:07         ` Len Brown
2021-08-31 22:11           ` Dave Hansen
2021-08-30 18:04       ` Dave Hansen [this message]
2021-08-31 22:15         ` Len Brown
2021-08-31 22:16           ` Len Brown
2021-08-31 22:39           ` Thiago Macieira
2021-08-31 22:44             ` Len Brown
2021-07-30 14:59 ` [PATCH v9 13/26] x86/fpu/xstate: Support ptracer-induced XSTATE buffer expansion Chang S. Bae
2021-07-30 14:59 ` [PATCH v9 14/26] x86/arch_prctl: Create ARCH_SET_STATE_ENABLE/ARCH_GET_STATE_ENABLE Chang S. Bae
2021-08-06 16:46   ` Thiago Macieira
2021-08-09 22:08     ` Bae, Chang Seok
2021-08-09 23:42       ` Thiago Macieira
2021-08-10  0:57         ` Bae, Chang Seok
2021-08-13 19:44           ` Bae, Chang Seok
2021-07-30 14:59 ` [PATCH v9 15/26] x86/fpu/xstate: Support both legacy and expanded signal XSTATE size Chang S. Bae
2021-07-30 14:59 ` [PATCH v9 16/26] x86/fpu/xstate: Adjust the XSAVE feature table to address gaps in state component numbers Chang S. Bae
2021-07-30 14:59 ` [PATCH v9 17/26] x86/fpu/xstate: Disable XSTATE support if an inconsistent state is detected Chang S. Bae
2021-07-30 14:59 ` [PATCH v9 18/26] x86/cpufeatures/amx: Enumerate Advanced Matrix Extension (AMX) feature bits Chang S. Bae
2021-07-30 14:59 ` [PATCH v9 19/26] x86/fpu/amx: Define AMX state components and have it used for boot-time checks Chang S. Bae
2021-07-30 14:59 ` [PATCH v9 20/26] x86/fpu/amx: Initialize child's AMX state Chang S. Bae
2021-07-30 14:59 ` [PATCH v9 21/26] x86/fpu/amx: Enable the AMX feature in 64-bit mode Chang S. Bae
2021-07-30 14:59 ` [PATCH v9 22/26] x86/fpu/xstate: Skip writing zeros to signal frame for dynamic user states if in INIT-state Chang S. Bae
2021-07-30 14:59 ` [PATCH v9 23/26] selftest/x86/amx: Test cases for the AMX state management Chang S. Bae
2021-07-30 14:59 ` [PATCH v9 24/26] x86/insn/amx: Add TILERELEASE instruction to the opcode map Chang S. Bae
2021-07-30 14:59 ` [PATCH v9 25/26] intel_idle/amx: Add SPR support with XTILEDATA capability Chang S. Bae
2021-07-30 18:41   ` Dave Hansen
2021-08-03 21:32     ` Bae, Chang Seok
2021-08-03 21:38       ` Dave Hansen
2021-08-03 21:43         ` Brown, Len
2021-07-30 20:15   ` Dave Hansen
2021-07-30 14:59 ` [PATCH v9 26/26] x86/fpu/xstate: Add a sanity check for XFD state when saving XSTATE Chang S. Bae

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