Re: [PATCH v2 2/2] x86/xstate: also use alternative asm on xsave side

[Andrew Cooper <andrew.cooper3@citrix.com>]

On 03/02/16 12:39, Jan Beulich wrote:
> From: Shuai Ruan <shuai.ruan@linux.intel.com>
>
> This patch use alternavtive asm on the xsave side.
> As xsaves use modified optimization like xsaveopt, xsaves
> may not writing the FPU portion of the save image too.
> So xsaves also need some extra tweaks.
>
> Signed-off-by: Shuai Ruan <shuai.ruan@linux.intel.com>
>
> Fix XSAVES opcode. Extend the other respective XSAVEOPT conditional to
> cover XSAVES as well. Re-wrap comment being adjusted.
>
> Signed-off-by: Jan Beulich <jbeulich@suse.com>
>
> --- a/xen/arch/x86/xstate.c
> +++ b/xen/arch/x86/xstate.c
> @@ -250,27 +250,29 @@ void xsave(struct vcpu *v, uint64_t mask
>      uint32_t hmask = mask >> 32;
>      uint32_t lmask = mask;
>      int word_size = mask & XSTATE_FP ? (cpu_has_fpu_sel ? 8 : 0) : -1;
> +#define XSAVE(pfx) \
> +        alternative_io_3(".byte " pfx "0x0f,0xae,0x27\n", \
> +                         ".byte " pfx "0x0f,0xae,0x37\n", \
> +                         X86_FEATURE_XSAVEOPT, \
> +                         ".byte " pfx "0x0f,0xc7,0x27\n", \
> +                         X86_FEATURE_XSAVEC, \
> +                         ".byte " pfx "0x0f,0xc7,0x2f\n", \
> +                         X86_FEATURE_XSAVES, \

Given that the options are a little out of order and using raw bytes,
would you mind annotating the lines with the operations. e.g.

+        alternative_io_3(".byte " pfx "0x0f,0xae,0x27\n", /* xsave */ \
+                         ".byte " pfx "0x0f,0xae,0x37\n", /* xsaveopt */ \
+                         X86_FEATURE_XSAVEOPT, \
+                         ".byte " pfx "0x0f,0xc7,0x27\n", /* xsavec */ \
+                         X86_FEATURE_XSAVEC, \
+                         ".byte " pfx "0x0f,0xc7,0x2f\n", /* xsaves */ \
+                         X86_FEATURE_XSAVES, \

IMO, this is somewhat clearer to read.

Otherwise,

Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>