linux-kernel - Re: [PATCH 03/11] x86/fpu: make __raw_xsave_addr() use feature number instead of mask

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Date:   Fri, 12 Oct 2018 08:52:03 -0700
From:   Dave Hansen <dave.hansen@...ux.intel.com>
To:     Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        linux-kernel@...r.kernel.org
Cc:     x86@...nel.org, Andy Lutomirski <luto@...nel.org>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Radim Krčmář <rkrcmar@...hat.com>,
        kvm@...r.kernel.org, "Jason A. Donenfeld" <Jason@...c4.com>,
        Rik van Riel <riel@...riel.com>
Subject: Re: [PATCH 03/11] x86/fpu: make __raw_xsave_addr() use feature number
 instead of mask

On 10/04/2018 07:05 AM, Sebastian Andrzej Siewior wrote:
> Most users of __raw_xsave_addr() use a feature number, shift it to a
> mask and then __raw_xsave_addr() shifts it back to the feature number.
> 
> Make __raw_xsave_addr() use the feature number as argument.

This generally looks like a nice cleanup.  Thanks for taking a look at it!

> diff --git a/arch/x86/kernel/fpu/xstate.c b/arch/x86/kernel/fpu/xstate.c
> index 87a57b7642d36..38d0b5ea40425 100644
> --- a/arch/x86/kernel/fpu/xstate.c
> +++ b/arch/x86/kernel/fpu/xstate.c
> @@ -811,10 +811,8 @@ void fpu__resume_cpu(void)
>   *
>   * Note: does not work for compacted buffers.
>   */
> -void *__raw_xsave_addr(struct xregs_state *xsave, int xstate_feature_mask)
> +void *__raw_xsave_addr(struct xregs_state *xsave, int feature_nr)
>  {

Could we call this 'xfeature_nr' consistently?

> -	int feature_nr = fls64(xstate_feature_mask) - 1;
> -
>  	if (!xfeature_enabled(feature_nr)) {
>  		WARN_ON_FPU(1);
>  		return NULL;
> @@ -842,6 +840,7 @@ void *__raw_xsave_addr(struct xregs_state *xsave, int xstate_feature_mask)
>   */
>  void *get_xsave_addr(struct xregs_state *xsave, int xstate_feature)
>  {
> +	int feature_nr;
>  	/*
>  	 * Do we even *have* xsave state?
>  	 */
> @@ -869,7 +868,8 @@ void *get_xsave_addr(struct xregs_state *xsave, int xstate_feature)
>  	if (!(xsave->header.xfeatures & xstate_feature))
>  		return NULL;
>  
> -	return __raw_xsave_addr(xsave, xstate_feature);
> +	feature_nr = fls64(xstate_feature) - 1;
> +	return __raw_xsave_addr(xsave, feature_nr);
>  }

Should we also be using a feature number for get_xsave_addr()?  In other
words, could you take a look and see how widely we should be doing this
kind of conversion and not just limit it to __raw_xsave_addr()?