Re: commit 3c2e7f7de3 (KVM use NPT page attributes) causes boot failures

[Xiao Guangrong]

On 09/02/2015 05:38 PM, Markus Trippelsdorf wrote:
> On 2015.09.02 at 17:17 +0800, Xiao Guangrong wrote:
> > > No. PAT is of course enabled and booting is successful sometimes even
> > > with the BUG() in allback_mtrr_type(). I suspect a setup (timing) issue.
> >
> > Thanks for your confirmation.
> >
> > > markus@x4 linux % cat .config | grep  X86_PAT
> > > CONFIG_X86_PAT=y
> > > markus@x4 linux % dmesg | grep PAT
> > > [    0.000000] x86/PAT: Configuration [0-7]: WB  WC  UC- UC  WB  WC  UC- WT
> >
> > Strange, BP processor has already set WC to PAT1, however KVM does not read it out
> > from PAT MSR on its local CPU.
> >
> > Hmm... PAT default values do not include WC, it seems initing PAT on SP has not
> > finished after module_init()?
> >
> > Could please apply this diff and test it again?
>
> (Your patch was malformed.)
>
> [    2.138098] kvm: Nested Virtualization enabled
> [    2.138153] kvm: Nested Paging enabled
> [    2.138204] KVM PAT: 0x7040600070406.

So the PAT is the value after CPU reset, it's likely PAT is not initialized on
the local CPU.

Maybe something is escaped from stop_machine() called in native_smp_cpus_done(),
Ingo?
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