Re: [Xen-devel] X86EMUL_CMPXCHG_FAILED

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 11.10.17 at 15:59, <rcojocaru@xxxxxxxxxxxxxxx> wrote:
> Now that "x86/hvm: implement hvmemul_write() using real mappings" is in, 
> we can start working again on implementing hvmemul_cmpxchg() with a real 
> CMPXCHG, and finally fix the SMP emulation race upstream.

That's my plan, but this will end up being complete only with the
RMW patch I had also posted, and which now can be made use
of the hvm/emulate.c. I'm intending to get to this as soon as
time permits.

> However, in order to do that we would need X86EMUL_CMPXCHG_FAILED which 
> has been dropped by Andrew here:
> 
> https://patchwork.kernel.org/patch/9449339/ 
> 
> and re-contributed by Jan here:
> 
> https://patchwork.kernel.org/patch/9651613/ 
> 
> (the patch is a combination of Jan's patch and my fumbling with CMPXCHG).
> 
> However, I remember Jan saying that his patch is no longer the way to go 
> here. How should we proceed?

Well, the patch will need some re-working, so that the end result will
fit with the RMW one (in particular I also want to eliminate the multiple
reads issue we have), but right now I don't recall any reason why it
wouldn't be suitable (anymore) at all.

But this is all work targeted at 4.11, so not really a need to rush.

Jan


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