Re: [Xen-devel] Debian stable kernel got timer issue when running as PV guest

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 12.04.12 at 21:22, Sheng Yang <sheng@xxxxxxxxxx> wrote:
> I've compiled a kernel, force sched_clock_stable=0, then it solved the
> timestamp jump issue as expected. Luckily, seems it also solved the call
> trace and guest hang issue as well.

And this is also how it should be fixed.

> Attachment is a (untested) patch to mask the CPUID leaf 0x80000007. I think
> the issue can be easily reproduced using a Westmere or SandyBridge
> machine(my old colleagues at Intel said the feature likely existed after
> Nehalem) running newer version of PV guest, check the guest cpuinfo you
> would see nonstop_tsc, and you would notice the abnormal timestamp of
> printk.

Masking the entire leaf is certainly out of question. And even masking
the individual bit is questionable - a PV kernel simply shouldn't look at
it imo (for other than possibly reporting to user mode purposes).

Jan


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