Re: [PATCH v2 04/12] x86/xen: drop USERGS_SYSRET64 paravirt call

[Borislav Petkov]

On Wed, Dec 02, 2020 at 03:48:21PM +0100, Jürgen Groß wrote:
> I wanted to avoid the additional NOPs for the bare metal case.

Yeah, in that case it gets optimized to a single NOP:

[    0.176692] SMP alternatives: ffffffff81a00068: [0:5) optimized NOPs: 0f 1f 44 00 00

which is nopl 0x0(%rax,%rax,1) and I don't think that's noticeable on
modern CPUs where a NOP is basically a rIP increment only and that goes
down the pipe almost for free. :-)

> If you don't mind them I can do as you are suggesting.

Yes pls, I think asm readability is more important than a 5-byte NOP.

Thx.

-- 
Regards/Gruss,
    Boris.

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