Re: [Xen-devel] reading IOPL

[Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>]

On Thu, May 03, 2012 at 05:07:04PM +0100, Jan Beulich wrote:
> Both Linux and Xen offer only ways to set the IOPL. While on native Linux
> this is not a problem since user mode code can read the IOPL by inspecting
> EFLAGS, on Xen this would always yield zero.
> 
> Now X folks appear to be using save-modify-restore cycles in some newer
> code, and this obviously breaks under Xen, as they would restore IOPL 0

This is in the KMS drivers or in the user-land Xorg?

> even when IOPL 3 was in effect before.
> 
> Since the only way to read the IOPL is xc_vcpu_getcontext() (i.e.
> XEN_DOMCTL_getvcpucontext), I wonder whether we shouldn't add
> e.g. a "get" counterpart to PHYSDEVOP_set_iopl.
> 
> Or am I overlooking some other access mechanism?
> 
> Jan
> 
> 
> 
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