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From: "Bae, Chang Seok" <chang.seok.bae@intel.com>
To: Jann Horn <jannh@google.com>
Cc: Borislav Petkov <bp@suse.de>, Andy Lutomirski <luto@kernel.org>,
	"Thomas Gleixner" <tglx@linutronix.de>,
	Ingo Molnar <mingo@kernel.org>,
	"the arch/x86 maintainers" <x86@kernel.org>,
	"Brown, Len" <len.brown@intel.com>,
	"Hansen, Dave" <dave.hansen@intel.com>,
	"Liu, Jing2" <jing2.liu@intel.com>,
	"Shankar, Ravi V" <ravi.v.shankar@intel.com>,
	kernel list <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH v4 14/22] x86/fpu/xstate: Expand the xstate buffer on the first use of dynamic user state
Date: Mon, 29 Mar 2021 18:14:48 +0000	[thread overview]
Message-ID: <138A0E3D-4794-43C7-861A-4011534A09A8@intel.com> (raw)
In-Reply-To: <CAG48ez3hLjwirUoaanDHJ_2h73YruVxfJL88AFVoym7sy02a5w@mail.gmail.com>

On Mar 26, 2021, at 09:34, Jann Horn <jannh@google.com> wrote:
> On Sun, Feb 21, 2021 at 7:56 PM Chang S. Bae <chang.seok.bae@intel.com> wrote:
>> 
>> +       if (handle_xfirstuse_event(&current->thread.fpu))
>> +               return;
> 
> What happens if handle_xfirstuse_event() fails because vmalloc()
> failed in alloc_xstate_buffer()? I think that should probably kill the
> task with something like force_sig() - but as far as I can tell, at
> the moment, it will instead end up at die(), which should only be used
> for kernel bugs.

This question was raised on v1 before [1].

In the end, people suggested to handle the failure, e.g., with tracepoints or
stats. So, proposed this on the allocation site:

+	state_ptr = vmalloc(newsz);
+	if (!state_ptr) {
+		trace_x86_fpu_xstate_alloc_failed(fpu);
+		return -ENOMEM;
+	}

Also, I tried to justify this to Boris [2]:

  >> Maybe it is possible to backtrack this allocation failure out of #NM
  >> handling. But the tracepoint can provide a clear context, although limited
  >> to those using it.

  > Yes, add it when it is really needed. Not slapping it proactively and
  > hoping for any potential usage.

Let me know if you have a better way.

Thanks,
Chang

[1] https://lore.kernel.org/lkml/c4669d5f-11b8-3879-562c-78a791b86229@intel.com/
[2] https://lore.kernel.org/lkml/20210204131002.GA17068@zn.tnic/


  reply	other threads:[~2021-03-29 18:15 UTC|newest]

Thread overview: 78+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-02-21 18:56 [PATCH v4 00/22] x86: Support Intel Advanced Matrix Extensions Chang S. Bae
2021-02-21 18:56 ` [PATCH v4 01/22] x86/fpu/xstate: Modify the initialization helper to handle both static and dynamic buffers Chang S. Bae
2021-03-10 13:40   ` Borislav Petkov
2021-02-21 18:56 ` [PATCH v4 02/22] x86/fpu/xstate: Modify state copy helpers " Chang S. Bae
2021-02-21 18:56 ` [PATCH v4 03/22] x86/fpu/xstate: Modify address finders " Chang S. Bae
2021-02-21 18:56 ` [PATCH v4 04/22] x86/fpu/xstate: Modify the context restore helper " Chang S. Bae
2021-02-21 18:56 ` [PATCH v4 05/22] x86/fpu/xstate: Add a new variable to indicate dynamic user states Chang S. Bae
2021-02-21 18:56 ` [PATCH v4 06/22] x86/fpu/xstate: Add new variables to indicate dynamic xstate buffer size Chang S. Bae
2021-02-21 18:56 ` [PATCH v4 07/22] x86/fpu/xstate: Calculate and remember dynamic xstate buffer sizes Chang S. Bae
2021-02-21 18:56 ` [PATCH v4 08/22] x86/fpu/xstate: Convert the struct fpu 'state' field to a pointer Chang S. Bae
2021-02-21 18:56 ` [PATCH v4 09/22] x86/fpu/xstate: Introduce helpers to manage the xstate buffer dynamically Chang S. Bae
2021-02-21 18:56 ` [PATCH v4 10/22] x86/fpu/xstate: Define the scope of the initial xstate data Chang S. Bae
2021-02-21 18:56 ` [PATCH v4 11/22] x86/fpu/xstate: Update the xstate save function to support dynamic states Chang S. Bae
2021-02-21 18:56 ` [PATCH v4 12/22] x86/fpu/xstate: Update the xstate buffer address finder " Chang S. Bae
2021-02-21 18:56 ` [PATCH v4 13/22] x86/fpu/xstate: Update the xstate context copy function " Chang S. Bae
2021-02-21 18:56 ` [PATCH v4 14/22] x86/fpu/xstate: Expand the xstate buffer on the first use of dynamic user state Chang S. Bae
2021-03-20 22:13   ` Thomas Gleixner
2021-03-20 22:21     ` Andy Lutomirski
2021-03-23 21:01       ` Len Brown
2021-03-24  3:14         ` Liu, Jing2
2021-03-24 21:09           ` Len Brown
2021-03-24 21:26             ` Andy Lutomirski
2021-03-24 21:30               ` Dave Hansen
2021-03-24 21:42                 ` Andy Lutomirski
2021-03-24 21:58                   ` Dave Hansen
2021-03-24 22:12                     ` Andy Lutomirski
2021-03-25  5:12             ` Liu, Jing2
2021-03-25  6:59               ` Bae, Chang Seok
2021-03-25  7:26                 ` Liu, Jing2
2021-03-23 21:52     ` Bae, Chang Seok
2021-03-24 14:24       ` Dave Hansen
2021-03-29 13:14     ` Len Brown
2021-03-29 13:33       ` Thomas Gleixner
2021-03-29 15:43         ` Len Brown
2021-03-29 16:06           ` Len Brown
2021-03-29 17:43             ` Andy Lutomirski
2021-03-29 18:57               ` Len Brown
2021-03-29 18:49           ` Thomas Gleixner
2021-03-29 22:16             ` Len Brown
2021-03-30  8:28               ` Thomas Gleixner
2021-03-30 16:38                 ` Len Brown
2021-03-26 16:34   ` Jann Horn
2021-03-29 18:14     ` Bae, Chang Seok [this message]
2021-02-21 18:56 ` [PATCH v4 15/22] x86/fpu/xstate: Support ptracer-induced xstate buffer expansion Chang S. Bae
2021-02-21 18:56 ` [PATCH v4 16/22] x86/fpu/xstate: Extend the table to map state components with features Chang S. Bae
2021-03-20 21:25   ` Thomas Gleixner
2021-03-23 21:52     ` Bae, Chang Seok
2021-02-21 18:56 ` [PATCH v4 17/22] x86/cpufeatures/amx: Enumerate Advanced Matrix Extension (AMX) feature bits Chang S. Bae
2021-02-21 18:56 ` [PATCH v4 18/22] x86/fpu/amx: Define AMX state components and have it used for boot-time checks Chang S. Bae
2021-03-20 21:31   ` Thomas Gleixner
2021-03-23 21:52     ` Bae, Chang Seok
2021-02-21 18:56 ` [PATCH v4 19/22] x86/fpu/amx: Enable the AMX feature in 64-bit mode Chang S. Bae
2021-03-20 21:26   ` Thomas Gleixner
2021-03-23 21:51     ` Bae, Chang Seok
2021-02-21 18:56 ` [PATCH v4 20/22] selftest/x86/amx: Include test cases for the AMX state management Chang S. Bae
2021-02-21 18:56 ` [PATCH v4 21/22] x86/fpu/xstate: Support dynamic user state in the signal handling path Chang S. Bae
2021-02-21 18:56 ` [PATCH v4 22/22] x86/fpu/xstate: Introduce boot-parameters to control state component support Chang S. Bae
2021-02-21 19:30   ` Randy Dunlap
2021-02-21 20:10     ` Bae, Chang Seok
2021-02-21 20:37       ` Randy Dunlap
2021-03-20 20:56   ` Thomas Gleixner
2021-03-25 22:59     ` Len Brown
2021-03-25 23:10       ` Dave Hansen
2021-03-26 15:27         ` Len Brown
2021-03-26 19:22           ` Thomas Gleixner
2021-03-26  1:41       ` Andy Lutomirski
2021-03-26 15:33         ` Len Brown
2021-03-26 15:48           ` Andy Lutomirski
2021-03-26 17:53             ` Len Brown
2021-03-26 18:12               ` Andy Lutomirski
2021-03-27  4:53                 ` Len Brown
2021-03-27 22:20                   ` Thomas Gleixner
2021-03-29 13:31                     ` Len Brown
2021-03-29 14:10                       ` Thomas Gleixner
2021-03-26 18:17               ` Borislav Petkov
2021-03-27  4:41                 ` Len Brown
2021-03-26  1:50       ` Thomas Gleixner
2021-03-26 15:36         ` Len Brown

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