Re: [Xen-devel] Initialising MXCSR in PV guests

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 30.11.12 at 18:14, Anil Madhavapeddy <anil@xxxxxxxxxx> wrote:
> We're seeing floating point exceptions on some (but not all) machines when 
> doing FP operations inside MiniOS.
> 
> It looks like the FPU and SSE control registers are not set to good default 
> values (which by default mask various FP exceptions) when MiniOS is started 
> as a PV guest. If the call to fpu_init below is not made, the division 
> generates a precision error and fails.  
> 
> Do PV guests all need to explicitly initialise MXCSR, or has something 
> changed in Xen to trigger this now?  It seems to have been set in the past, 
> and only happens on some hosts.

As you're not telling us where you do and do not observe this bad
behavior, I'm wondering if you're simply running into the issue
addressed by -unstable c/s 24157:7b5e1cb94bfa.

Jan


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