* Linux'es SLUB incompatible with Xen?
@ 2014-09-25 8:23 Jan Beulich
2014-09-25 10:08 ` Ian Campbell
2014-09-25 10:47 ` David Vrabel
0 siblings, 2 replies; 6+ messages in thread
From: Jan Beulich @ 2014-09-25 8:23 UTC (permalink / raw)
To: David Vrabel, Boris Ostrovsky, Konrad Rzeszutek Wilk
Cc: Juergen Gross, xen-devel
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)?
Jan
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: Linux'es SLUB incompatible with Xen?
2014-09-25 8:23 Linux'es SLUB incompatible with Xen? Jan Beulich
@ 2014-09-25 10:08 ` Ian Campbell
2014-09-25 10:53 ` Jan Beulich
2014-09-25 10:47 ` David Vrabel
1 sibling, 1 reply; 6+ messages in thread
From: Ian Campbell @ 2014-09-25 10:08 UTC (permalink / raw)
To: Jan Beulich; +Cc: Juergen Gross, xen-devel, Boris Ostrovsky, David Vrabel
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?
Ian.
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: Linux'es SLUB incompatible with Xen?
2014-09-25 10:08 ` Ian Campbell
@ 2014-09-25 10:53 ` Jan Beulich
2014-09-25 10:57 ` Ian Campbell
0 siblings, 1 reply; 6+ messages in thread
From: Jan Beulich @ 2014-09-25 10:53 UTC (permalink / raw)
To: Ian Campbell; +Cc: Juergen Gross, xen-devel, Boris Ostrovsky, David Vrabel
>>> On 25.09.14 at 12:08, <Ian.Campbell@citrix.com> 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.
Jan
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: Linux'es SLUB incompatible with Xen?
2014-09-25 10:53 ` Jan Beulich
@ 2014-09-25 10:57 ` Ian Campbell
0 siblings, 0 replies; 6+ messages in thread
From: Ian Campbell @ 2014-09-25 10:57 UTC (permalink / raw)
To: Jan Beulich; +Cc: Juergen Gross, xen-devel, Boris Ostrovsky, David Vrabel
On Thu, 2014-09-25 at 11:53 +0100, Jan Beulich wrote:
> >>> On 25.09.14 at 12:08, <Ian.Campbell@citrix.com> 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.
Sorry, I somehow missed the parenthetical bit in middle of the
paragraph!
Ian.
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: Linux'es SLUB incompatible with Xen?
2014-09-25 8:23 Linux'es SLUB incompatible with Xen? Jan Beulich
2014-09-25 10:08 ` Ian Campbell
@ 2014-09-25 10:47 ` David Vrabel
2014-09-26 18:12 ` Konrad Rzeszutek Wilk
1 sibling, 1 reply; 6+ messages in thread
From: David Vrabel @ 2014-09-25 10:47 UTC (permalink / raw)
To: Jan Beulich, Boris Ostrovsky, Konrad Rzeszutek Wilk
Cc: Juergen Gross, xen-devel
On 25/09/14 09:23, 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)?
I wasn't aware but I don't care about such old hardware so I'm not going
to fix it.
If you think this should be fixed, please work with the x86 maintainers
to get this fixed.
David
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: Linux'es SLUB incompatible with Xen?
2014-09-25 10:47 ` David Vrabel
@ 2014-09-26 18:12 ` Konrad Rzeszutek Wilk
0 siblings, 0 replies; 6+ messages in thread
From: Konrad Rzeszutek Wilk @ 2014-09-26 18:12 UTC (permalink / raw)
To: David Vrabel; +Cc: Juergen Gross, xen-devel, Boris Ostrovsky, Jan Beulich
On Thu, Sep 25, 2014 at 11:47:23AM +0100, David Vrabel wrote:
> On 25/09/14 09:23, 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)?
>
> I wasn't aware but I don't care about such old hardware so I'm not going
> to fix it.
>
> If you think this should be fixed, please work with the x86 maintainers
> to get this fixed.
HAHAHA
You are such a comedian :-)
>
> David
^ permalink raw reply [flat|nested] 6+ messages in thread
end of thread, other threads:[~2014-09-26 18:12 UTC | newest]
Thread overview: 6+ messages (download: mbox.gz follow: Atom feed
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2014-09-25 8:23 Linux'es SLUB incompatible with Xen? Jan Beulich
2014-09-25 10:08 ` Ian Campbell
2014-09-25 10:53 ` Jan Beulich
2014-09-25 10:57 ` Ian Campbell
2014-09-25 10:47 ` David Vrabel
2014-09-26 18:12 ` Konrad Rzeszutek Wilk
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