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

From: Xiao Guangrong
Date: Wed Sep 02 2015 - 06:33:25 EST

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
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(),
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