Re: [Xen-devel] fxsave, fnsave, ltr hang for guest OS.

[Keir Fraser <keir@xxxxxxx>]

On 19/11/2010 17:32, "alarson@xxxxxxxx" <alarson@xxxxxxxx> wrote:

> Just to report final resolution.  The problem turned out to be that
> the destination of the fnsave was to a page specifying read only
> access and the OS was depending on CR0.WP=0 to permit write access in
> kernel mode.  Xen doesn't allow this configuration unless using HAP
> (Hardware Assisted Paging).

To be precise, we have a go at emulating the instruction, but our emulator
is incomplete. Running a whole OS in CR0.WP=0 mode is pretty much doomed if
running on Xen without HAP. I think there is some supported OS that does do
some small amount of stuff with CR0.WP=0, and we are complete enough to work
in that case.

 -- Keir

> Many thanks to Keir for his invaluable assistance with this.



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