Re: [PATCH v5 06/39] x86/fpu: Add helper for modifying xstate

On Wed, Feb 01, 2023 at 05:31:50PM +0000, Edgecombe, Rick P wrote:

On Wed, 2023-02-01 at 12:01 +0100, Borislav Petkov wrote:

quoted

On Thu, Jan 19, 2023 at 01:22:44PM -0800, Rick Edgecombe wrote:

quoted

+void fpregs_lock_and_load(void)
+{
+     /*
+      * fpregs_lock() only disables preemption (mostly). So
modifying state
+      * in an interrupt could screw up some in progress fpregs
operation,
+      * but appear to work. Warn about it.

I don't like comments where it sounds like we don't know what we're
doing. "Appear to work"?

I can change it. This patch started with the observation that modifying
xstate from the kernel had been gotten wrong a couple times in the
past, so that is what this is referencing. Since then, the fancy
automatic solution got boiled down to this helper and a couple
warnings.

Yeah, but that comment right now reads like: modifying in interrupt
context can corrupt fpregs and you should not do it but it kinda works,
by chance. Thus encouraging people to keep doing that.

I guess "but appear to work" can go and then it is fine.

Thx.

-- 
Regards/Gruss,
    Boris.

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