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From: Yu-cheng Yu <yu-cheng.yu@intel.com>
To: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc: linux-kernel@vger.kernel.org, x86@kernel.org,
	"H. Peter Anvin" <hpa@zytor.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	Ingo Molnar <mingo@redhat.com>,
	Dave Hansen <dave.hansen@linux.intel.com>,
	Tony Luck <tony.luck@intel.com>,
	Andy Lutomirski <luto@kernel.org>, Borislav Petkov <bp@alien8.de>,
	Rik van Riel <riel@surriel.com>,
	"Ravi V. Shankar" <ravi.v.shankar@intel.com>,
	Fenghua Yu <fenghua.yu@intel.com>,
	Peter Zijlstra <peterz@infradead.org>
Subject: Re: [PATCH v2 3/3] x86/fpu/xstate: Invalidate fpregs when __fpu_restore_sig() fails
Date: Thu, 19 Dec 2019 09:40:06 -0800
Message-ID: <1607597639a6c6255127fef07704ee9193e33166.camel@intel.com> (raw)
In-Reply-To: <20191219171635.phdsfkvsyazwaq7s@linutronix.de>

On Thu, 2019-12-19 at 18:16 +0100, Sebastian Andrzej Siewior wrote:
> On 2019-12-19 08:44:08 [-0800], Yu-cheng Yu wrote:
> > Yes, this works.  But then everywhere that calls copy_*_to_xregs_*() etc. needs to be checked.
> > Are there other alternatives?
> 
> I don't like the big hammer approach of your very much. It might make
> all it "correct" but then it might lead to more "invalids" then needed.
> It also required to export the symbol which I would like to avoid.

Copying to registers invalids current fpregs context.  It might not cause
extra register loading, because registers are in fact already invalidated
and any task owning the context needs to reload anyway.  Setting
fpu_fpregs_owner_ctx is only to let the rest of the kernel know the
fact that already happened.

But, I agree with you the patch does look biggish.

> 
> So if this patch works for you and you don't find anything else where it
> falls apart then I will audit tomorrow all callers which got the
> "invalidator" added and check for that angle.

Yes, that works for me.  Also, most of these call sites are under fpregs_lock(),
and we could use __cpu_invalidate_fpregs_state().

I was also thinking maybe add warnings when any new code re-introduces the issue,
but not sure where to add that.  Do you think that is needed?

Thanks,
Yu-cheng


  reply index

Thread overview: 25+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-12-12 21:08 [PATCH v2 0/3] Fix small issues in XSAVES Yu-cheng Yu
2019-12-12 21:08 ` [PATCH v2 1/3] x86/fpu/xstate: Fix small issues before adding supervisor xstates Yu-cheng Yu
2019-12-20 20:19   ` Sebastian Andrzej Siewior
2020-01-06 18:15   ` [tip: x86/fpu] x86/fpu/xstate: Fix small issues tip-bot2 for Yu-cheng Yu
2019-12-12 21:08 ` [PATCH v2 2/3] x86/fpu/xstate: Make xfeature_is_supervisor()/xfeature_is_user() return bool Yu-cheng Yu
2019-12-20 20:19   ` Sebastian Andrzej Siewior
2019-12-20 20:33     ` Yu-cheng Yu
2020-01-06 18:15   ` [tip: x86/fpu] " tip-bot2 for Yu-cheng Yu
2019-12-12 21:08 ` [PATCH v2 3/3] x86/fpu/xstate: Invalidate fpregs when __fpu_restore_sig() fails Yu-cheng Yu
2019-12-18 15:54   ` Sebastian Andrzej Siewior
2019-12-18 20:53     ` Yu-cheng Yu
2019-12-19 14:22       ` Sebastian Andrzej Siewior
2019-12-19 16:44         ` Yu-cheng Yu
2019-12-19 17:16           ` Sebastian Andrzej Siewior
2019-12-19 17:40             ` Yu-cheng Yu [this message]
2019-12-20 19:59               ` [PATCH] x86/fpu: Deacticate FPU state after failure during state load Sebastian Andrzej Siewior
2020-01-07 12:52                 ` [tip: x86/fpu] x86/fpu: Deactivate " tip-bot2 for Sebastian Andrzej Siewior
2020-01-07 20:41                   ` Andy Lutomirski
2020-01-07 20:38                     ` Yu-cheng Yu
2020-01-07 21:11                     ` Sebastian Andrzej Siewior
2020-01-08 11:45                       ` Borislav Petkov
2020-01-08 11:46                     ` Borislav Petkov
2019-12-20 20:16               ` [PATCH v2 3/3] x86/fpu/xstate: Invalidate fpregs when __fpu_restore_sig() fails Sebastian Andrzej Siewior
2019-12-20 20:32                 ` Yu-cheng Yu
  -- strict thread matches above, loose matches on Subject: below --
2019-12-05 18:26 [PATCH " Yu-cheng Yu
2019-12-07  4:38 ` [PATCH v2 " Yu-cheng Yu

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