I made some more experiments on my Pentium-M laptop
(32-bit, non-PAE cpu), and found out that if I disable that
panic("Processor does not support PAE") call in
usr/src/uts/i86pc/vm/hat_i86.c, then I can boot a dom0
kernel just fine using the standard PAE enabled hypervisor:
diff -r 7aad25c79a0f usr/src/uts/i86pc/vm/hat_i86.c
--- a/usr/src/uts/i86pc/vm/hat_i86.c Fri Oct 26 11:18:55 2007 -0700
+++ b/usr/src/uts/i86pc/vm/hat_i86.c Sun Oct 28 01:58:29 2007 +0200
@@ -516,7 +516,11 @@ mmu_init(void)
}
if (mmu.pae_hat && (x86_feature & X86_PAE) == 0)
+#if defined(__xpv)
+ cmn_err(CE_NOTE, "Processor does not support PAE");
+#else
panic("Processor does not support PAE");
+#endif
if ((x86_feature & X86_CX8) == 0)
panic("Processor does not support cmpxchg8b instruction");
I get the notice that the processor does not support PAE, but it boots
just fine. A Solaris domU can be booted, too.
Can anyone explain what kind of mmu the hypervisor is emulating,
when it's compiled with with XEN_TARGET_X86_PAE=y?
It seems as if Xen offeres a PAE enabled mmu to a PV dom0/domU,
which dom0/domU can find out by searching for the xen capability
"xen-3.0-x86_32p"; the CPUID(1) %edx feature bit for the real
cpu's PAE feature might not be what needs for be checked to
find out if an mmu with or without PAE features is present in the
virtualized environment.
> The hypervisor must be compiled with PAE support or without it.
> That's just how the people who wrote the code made it.
> OpenSolaris use a version of the hypervisor compiled for PAE.
> If you download the source for the hypervisor, you
> could rebuild a version that didn't require PAE and use that instead.
>
> When running plain OpenSolaris (ie. no hypervisor) the solaris
> kernel automatically switches between using PAE or not based
> on the capabilites of the hardware, amount of memory, etc.
>
>
> James Cornell wrote:
> > Why does it need PAE? PAE is only for 4GB+ systems running in 32-bit
> > mode. This would normally be something not needed and/or disabled by
> > default. Pentium-M is vague, Core-based Centrino, Mobile Intel
> > Pentium 4, or Pentium 4 era Centrino? I'm guessing it's a Core-based
> > one since it's a Tectra, correct me if I'm wrong.
> Imho it wouldn't make sense for a reduced mode mobile processor to
> even have PAE, it can't even physically support more than 2GB in older
> "mobile" Intel processor systems.
>
> James
>
> On Oct 23, 2007, at 8:52 PM, Peter Schow wrote:
>
> > Attempting to boot xVM dom0 for the first time on a Toshiba Tecra M2
> >> running 75a.
> >>
> >> Getting a panic immediately after selecting xVM from the grub menu:
> >>
> >> panic[cpu0]/thread=f502c020: Processor does not support PAE
> >>
> >> This is a 2000 MHz Pentium-M, which I thought was PAE-capable.
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