linux-kernel - Re: [PATCH v2] x86/fpu: copy MXCSR & MXCSR

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Message-ID: <20170210000224.qgwwyozscwjegpqm@pd.tnic>
Date:   Fri, 10 Feb 2017 01:02:24 +0100
From:   Borislav Petkov <bp@...e.de>
To:     Rik van Riel <riel@...hat.com>
Cc:     mingo@...nel.org, linux-kernel@...r.kernel.org, luto@...nel.org,
        dave.hansen@...ux.intel.com, yu-cheng.yu@...el.com, hpa@...or.com
Subject: Re: [PATCH v2] x86/fpu: copy MXCSR & MXCSR_FLAGS with SSE/YMM state

On Thu, Feb 09, 2017 at 06:43:47PM -0500, Rik van Riel wrote:
> On Skylake CPUs I noticed that XRSTOR is unable to deal with xsave areas
> created by copyout_from_xsaves if the xstate has only SSE/YMM state, but
> no FP state. That is, xfeatures had XFEATURE_MASK_SSE set, but not
> XFEATURE_MASK_FP.
> 
> The reason is that part of the SSE/YMM state lives in the MXCSR and
> MXCSR_FLAGS fields of the FP area.
> 
> Ensure that whenever we copy SSE or YMM state around, the MXCSR and
> MXCSR_FLAGS fields are also copied around.
> 
> Signed-off-by: Rik van Riel <riel@...hat.com>
> ---
>  arch/x86/kernel/fpu/xstate.c | 44 ++++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 44 insertions(+)

...

> @@ -987,6 +1004,13 @@ int copy_xstate_to_kernel(void *kbuf, struct xregs_state *xsave, unsigned int of
>  
>  	}
>  
> +	if (xfeatures_need_mxcsr_copy(header.xfeatures)) {
> +		offset = offsetof(struct fxregs_state, mxcsr);
> +		size = sizeof(u64); // copy mxcsr & mxcsr_flags
				    ^^^^^^^^^^^^^^^^^^^^^^^^^^^

We don't do // comments, do we?

And side-line comments are always impairing the readability of the code
unless it is a struct's members or asm or so ...

-- 
Regards/Gruss,
    Boris.

SUSE Linux GmbH, GF: Felix Imendörffer, Jane Smithard, Graham Norton, HRB 21284 (AG Nürnberg)
--