Re: [Xen-devel] [PATCH 1/3] x86/alternatives: fully leverage automatic NOP filling

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 14/03/18 08:29, Jan Beulich wrote:
> As of commit 4008c71d7a ("x86/alt: Support for automatic padding
> calculations") there's no point having explict ASM_NOPn instances in
> alternatives anymore - drop them. As a result also drop the asm/nops.h
> inclusion from alternative.h, adding explicit inclusions in the two
> remaining C files needing them.
>
> While touching it also move the CR4_PV32_RESTORE definition out of the
> SMAP-specific conditional into a more general one.
>
> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>

I had considered doing this, but decided against it.  At the moment, the
majority of hardware Xen runs on (being Intel pre-broadwell) doesn't
need to touch the STAC/CLAC patch sites, and this change means we will
always touch those sites.

OTOH, (following up from later discussion) doing this does mean that we
would end up replacing with K8 nops when appropriate.

I'd like the toolchain-nops change to go in first, so we don't regress
the majority status quo, but I have no other issues with this change.

~Andrew

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