Re: [Xen-devel] Re: BUG: unable to handle kernel paging request at ffff8803bb6ad000

[Ian Campbell <ijc@xxxxxxxxxxxxxx>]

On Tue, 2011-10-11 at 09:36 +0100, Jan Beulich wrote:
> >>> On 11.10.11 at 10:02, Ian Campbell <ijc@xxxxxxxxxxxxxx> wrote:
> > On Tue, 2011-10-11 at 08:07 +0100, Jan Beulich wrote:
> >> >>> On 10.10.11 at 18:49, Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx> 
> >> >>> wrote:
> >> > On Sat, Oct 08, 2011 at 10:13:14AM +0400, rush wrote:
> >> >> OK, I tried it again, but Oops didn't gone.
> >> > .. snip..
> >> >>         echo    'Loading Xen 4.0-amd64 ...'
> >> >>         multiboot       /boot/xen-4.0-amd64.gz placeholder xsave=0
> >> > .. snip..
> >> >> Was it right?
> >> > 
> >> > Yup. I think.. this is a bit embarrassing. It took a bit of time for 
> >> > Intel
> >> > folks to get the xsave part right and I remember seeing this error about 
> >> > a
> >> > year ago with xsave on a Dell Optiplex 780. Hence I wonder if the fixes 
> > that
> >> > ultimately went in 4.1.1 did not get ported over to 4.0 and you are just
> >> > hitting that.
> >> > 
> >> > Can I ask you to do one more thing? Can you upgrade to the xen-4.1.1 in
> >> > the testing and try with the xsave (or without) and see if it works?
> >> > 
> >> > <holds his fingers hoping it is the xsave feature>
> >> 
> >> Are both of you certain this isn't the problem of the kernel only
> >> looking at the xsaveopt feature flag (implying that this means
> >> xsave is also available)? I found it necessary to force-clear that
> >> flag in the kernel when OSXSAVE is not set (by calling
> >> x86_xsave_setup() when !cpu_has_xsave, which in turn was
> >> modified to look at X86_FEATURE_OSXSAVE rather than
> >> X86_FEATURE_XSAVE under Xen - all of which I'm afraid would
> >> need to be done differently in pv-ops).
> > 
> > That all sounds familiar... In mainline we have (in
> > xen_init_cpuid_mask):
> > 
> >     ...
> >         xsave_mask =
> >                 (1 << (X86_FEATURE_XSAVE % 32)) |
> >                 (1 << (X86_FEATURE_OSXSAVE % 32));
> > 
> >         /* Xen will set CR4.OSXSAVE if supported and not disabled by force 
> > */
> >         if ((cx & xsave_mask) != xsave_mask)
> >                 cpuid_leaf1_ecx_mask &= ~xsave_mask; /* disable XSAVE & 
> > OSXSAVE */
> > 
> > Which I think implements something similar to what you describe? IOW
> > unless both XSAVE and OSXSAVE are available both are forcibly disabled.
> 
> Apart from the need to disable XSAVEOPT, yes.

Oh, right, I hadn't noticed it was a different/third flag.

> > While grepping I noticed that the kernel command line parameter to
> > disable xsave appears to be "noxsave" rather than "xsave=0", Rush is
> > that something you could try? (GRUB_CMDLINE_LINUX is the place to add
> > it)
> 
> Or "noxsaveopt" (if that's the problem, i.e. Rush's CPUs have that
> capability).

Right, Rush can you try both "noxsave" and "noxsaveopt" independently
please. If those work then we need to update the above logic to mask
xsaveopt as well.

Thanks,
Ian.

> 
> Jan
> 
> > Ian.
> > 
> >> If it is, the problem could be worked around by *en*abling xsave
> >> in Xen (which is off by default prior to 4.2), assuming none of the
> >> incomplete functionality would cause other headaches.
> >> 
> >> But yes, the CPUID handling code in 4.1.1 should properly hide
> >> XSAVEOPT when XSAVE is disabled, so just using this version
> >> ought to also get things going.
> >> 
> >> Jan
> >> 
> >> 
> >> _______________________________________________
> >> Xen-devel mailing list
> >> Xen-devel@xxxxxxxxxxxxxxxxxxx 
> >> http://lists.xensource.com/xen-devel 
> > 
> > -- 
> > Ian Campbell
> > Current Noise: Zyklon - Hammer Revelation
> > 
> > The ultimate game show will be the one where somebody gets killed at the 
> > end.
> >             -- Chuck Barris, creator of "The Gong Show"
> 
> 
> 
> 
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-- 
Ian Campbell
Current Noise: Zyklon - Transcendental War - Battle Between Gods

If you tell the truth you don't have to remember anything.
                -- Mark Twain


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