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From: Borislav Petkov <bp@alien8.de>
To: "Bae, Chang Seok" <chang.seok.bae@intel.com>
Cc: "Lutomirski, Andy" <luto@kernel.org>,
	"tglx@linutronix.de" <tglx@linutronix.de>,
	"mingo@kernel.org" <mingo@kernel.org>,
	"x86@kernel.org" <x86@kernel.org>,
	"Brown, Len" <len.brown@intel.com>,
	"Hansen, Dave" <dave.hansen@intel.com>,
	"Macieira, Thiago" <thiago.macieira@intel.com>,
	"Liu, Jing2" <jing2.liu@intel.com>,
	"Shankar, Ravi V" <ravi.v.shankar@intel.com>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH v9 08/26] x86/fpu/xstate: Introduce helpers to manage the XSTATE buffer dynamically
Date: Fri, 13 Aug 2021 12:04:43 +0200	[thread overview]
Message-ID: <YRZDu2Rk+KdRhh1U@zn.tnic> (raw)
In-Reply-To: <2BF12EDA-89F0-40F7-B63E-50ADD0262164@intel.com>

On Fri, Aug 13, 2021 at 08:04:54AM +0000, Bae, Chang Seok wrote:
> Yes, each state offset in the non-compacted format is fixed in a machine
> regardless of RFBM. So, simply take the size like that.

Comment above it please.

Also, why is this special case needed at all?

> But it might be better to simplify this hunk for readability. I
> suspect its call sites are not that performance-critical.

That's *exactly* what I'm driving at!

> Every task’s state_mask should begin as aligned with the default buffer.
> fpu_clone() sets this for all, except init_task.
> Maybe:
>     “Make sure init_task’s state_mask aligned with its __default_state"

Why "make sure"?

There's nothing to make sure - it is simply so that initially, the FPU
buffer used is the static one, without dynamic states. Just say that
instead.

> How about enlarge_xstate_buffer() or realloc_xstate_buffer()?

realloc is fine along with a proper explanation above it why the realloc
is done/needed.

> The query is intended to check whether the xstate buffer is fully expanded or
> not -- no need to enlarge.
> 
> If the buffer is already the maximum, the code to retrieve XSTATE_BV, this
> call, etc should be skipped there.  
> 
> If the query is moved here, I guess this call site code becomes a bit ugly.

Why does it become ugly?

You simply return early without touching the buffer at all.

> No, it is still pointed by fpu->state and will be freed in the exit path.

Exit path of the task?

All I see is "return -ENOMEM" and no callers of alloc_xstate_buffer()
are calling free_xstate_buffer()...

And looking further into the patchset:

exc_device_not_available does not call free_xstate_buffer() I'm assuming

	force_sig_fault(SIGILL, ILL_ILLOPC,..

later will cause arch_release_task_struct() to happen which will call
free_xstate_buffer(). Yes, no?

I don't see any freeing in xstateregs_set() either, so what's happening
there when it returns -ENOMEM?

I guess there we remain with the old buffer, i.e., the ptrace operation
fails.

Am I close?

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette

  reply	other threads:[~2021-08-13 10:04 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 [this message]
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
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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