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

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Date:   Thu, 11 Oct 2018 19:30:07 +0200
From:   Christophe de Dinechin <christophe.de.dinechin@...il.com>
To:     Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Cc:     linux-kernel@...r.kernel.org, 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>,
        Dave Hansen <dave.hansen@...ux.intel.com>
Subject: Re: [PATCH 03/11] x86/fpu: make __raw_xsave_addr() use feature number instead of mask


Sebastian Andrzej Siewior writes:

> 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.
>
> Signed-off-by: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
> ---
>  arch/x86/kernel/fpu/xstate.c | 16 ++++++++--------
>  1 file changed, 8 insertions(+), 8 deletions(-)
>
> 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)

It might be clearer to offer both interfaces, since both are used?

>  {
> -	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);

and then move that to a wrapper function that takes a mask?

>  }
>  EXPORT_SYMBOL_GPL(get_xsave_addr);
>
> @@ -1018,7 +1018,7 @@ int copy_xstate_to_kernel(void *kbuf, struct xregs_state *xsave, unsigned int of
>  		 * Copy only in-use xstates:
>  		 */
>  		if ((header.xfeatures >> i) & 1) {
> -			void *src = __raw_xsave_addr(xsave, 1 << i);
> +			void *src = __raw_xsave_addr(xsave, i);
>
>  			offset = xstate_offsets[i];
>  			size = xstate_sizes[i];
> @@ -1104,7 +1104,7 @@ int copy_xstate_to_user(void __user *ubuf, struct xregs_state *xsave, unsigned i
>  		 * Copy only in-use xstates:
>  		 */
>  		if ((header.xfeatures >> i) & 1) {
> -			void *src = __raw_xsave_addr(xsave, 1 << i);
> +			void *src = __raw_xsave_addr(xsave, i);
>
>  			offset = xstate_offsets[i];
>  			size = xstate_sizes[i];
> @@ -1161,7 +1161,7 @@ int copy_kernel_to_xstate(struct xregs_state *xsave, const void *kbuf)
>  		u64 mask = ((u64)1 << i);
>
>  		if (hdr.xfeatures & mask) {
> -			void *dst = __raw_xsave_addr(xsave, 1 << i);
> +			void *dst = __raw_xsave_addr(xsave, i);
>
>  			offset = xstate_offsets[i];
>  			size = xstate_sizes[i];
> @@ -1215,7 +1215,7 @@ int copy_user_to_xstate(struct xregs_state *xsave, const void __user *ubuf)
>  		u64 mask = ((u64)1 << i);
>
>  		if (hdr.xfeatures & mask) {
> -			void *dst = __raw_xsave_addr(xsave, 1 << i);
> +			void *dst = __raw_xsave_addr(xsave, i);
>
>  			offset = xstate_offsets[i];
>  			size = xstate_sizes[i];


--
Cheers,
Christophe de Dinechin (IRC c3d)