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Re: [Xen-devel] Linux'es SLUB incompatible with Xen?

>>> On 25.09.14 at 12:08, <Ian.Campbell@xxxxxxxxxx> wrote:
> On Thu, 2014-09-25 at 09:23 +0100, Jan Beulich wrote:
>> Linux-Xen maintainers,
>> are you aware that SLUB's use of percpu_cmpxchg16b_double() is
>> currently incompatible with Xen when run on old, not cmpxchg16b
>> capable x86-64 CPUs (the problem being this_cpu_cmpxchg16b_emu's
>> non-paravirtualized use of CLI)? Or is that a simple "we don't care -
>> don't run Xen on such old systems" (despite everything else, including
>> the hypervisor, working fine there)?
> Out of curiosity what is it about Xen that triggers this, as opposed to
> failing on native?

Not sure I understand the question: The emulation code that's being
used here is fine for native as CLI does what is expected. But for a
PV Xen guest CLI gets emulated as a privileged NOP, i.e. the needed
pseudo-atomicity isn't guaranteed.


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