Xen devel - Aug 2006 - virtualization of cr0 reg flags on hvm system

I''m experimenting with getting a fully virtualized i386 system up and
running on AMD HVM hardware under Xen.  (The reason for using i386 and
not amd64 is that the amd64 dies early in the kernel loading process.)

I have found that the kernel boots until it reaches a point where it
tries to load the cr0 register with the current cr0 value or''ed with a
set of flags.  In particular the load_cr0 call below never seems to
complete.  If I remove the CR0_WP (write-protect) flag, the kernel
continues booting.

I''m using xen unstable (tip''s changeset: 11217:6a8204e4619d). 
Is the
support of the WP flag a known issue?  Are there any fixes for it?


1224         cr0 = rcr0();
1225         /*
1226          * CR0_MP, CR0_NE and CR0_TS are also set by npx_probe() for the
1227          * BSP.  See the comments there about why we set them.
1228          */
1229         cr0 |= CR0_MP | CR0_NE | CR0_TS | CR0_WP | CR0_AM;
1230         load_cr0(cr0);

Thanks,
-Garth

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On 22/8/06 6:13 pm, "Garth Goodson" <ggoodson@gmail.com> wrote:
> I''m experimenting with getting a fully virtualized i386 system up
and
> running on AMD HVM hardware under Xen.  (The reason for using i386 and
> not amd64 is that the amd64 dies early in the kernel loading process.)
> 
> I have found that the kernel boots until it reaches a point where it
> tries to load the cr0 register with the current cr0 value or''ed
with a
> set of flags.  In particular the load_cr0 call below never seems to
> complete.  If I remove the CR0_WP (write-protect) flag, the kernel
> continues booting.
> 
> I''m using xen unstable (tip''s changeset:
11217:6a8204e4619d).  Is the
> support of the WP flag a known issue?  Are there any fixes for it?
Most OSes run with CR0.WP set all the time, so it''s certainly
supported. You
might need to add some tracing to Xen to find out why this particular write
to CR0 is failing for you.

 -- Keir



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