Re: [Xen-devel] [PATCH RFC for-4.13 08/10] xen/arm: alternative: add auto-nop infrastructure

[Stefano Stabellini <sstabellini@xxxxxxxxxx>]

On Fri, 27 Sep 2019, Volodymyr Babchuk wrote:
> Julien Grall writes:
> 
> > From: Mark Rutland <mark.rutland@xxxxxxx>
> >
> > In some cases, one side of an alternative sequence is simply a number of
> > NOPs used to balance the other side. Keeping track of this manually is
> > tedious, and the presence of large chains of NOPs makes the code more
> > painful to read than necessary.
> >
> > To ameliorate matters, this patch adds a new alternative_else_nop_endif,
> > which automatically balances an alternative sequence with a trivial NOP
> > sled.
> >
> > In many cases, we would like a NOP-sled in the default case, and
> > instructions patched in in the presence of a feature. To enable the NOPs
> > to be generated automatically for this case, this patch also adds a new
> > alternative_if, and updates alternative_else and alternative_endif to
> > work with either alternative_if or alternative_endif.
> >
> > The alternative infrastructure was originally ported from Linux. So this
> > is pretty much a straight backport from commit 792d47379f4d "arm64:
> > alternative: add auto-nop infrastructure". The only difference is the
> > nops macro added as not yet existing in Xen.
> >
> > Signed-off-by: Mark Rutland <mark.rutland@xxxxxxx>
> > [will: use new nops macro to generate nop sequences]
> > Signed-off-by: Will Deacon <will.deacon@xxxxxxx>
> > [julien: Add nops and port to Xen]
> > Signed-off-by: Julien Grall <julien.grall@xxxxxxx>
> Reviewed-by: Volodymyr Babchuk <volodymyr_babchuk@xxxxxxxx>

Acked-by: Stefano Stabellini <sstabellini@xxxxxxxxxx>

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