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

[Markus Trippelsdorf <markus@trippelsdorf.de>]

On 2015.09.02 at 06:31 +0800, Xiao Guangrong wrote:
> 
> 
> On 09/01/2015 09:56 PM, Markus Trippelsdorf wrote:
> > On 2015.09.01 at 21:00 +0800, Xiao Guangrong wrote:
> >>
> >> Did it trigger the BUG()/BUG_ON() in mtrr2protval()/fallback_mtrr_type()?
> >> If yes, could you please print the actual value out?
> >
> > It is the BUG() in fallback_mtrr_type(). I changed it to a printk and
> > it prints 1 for the value of mtrr.
> >
> >   MTRR_TYPE_WRCOMB     1
> >
> 
> Then I suspect pat is not enabled in your box, could you please check
> CONFIG_X86_PAT is selected in your .config file, pat is shown in
> /proc/cpuid, "nopat" kernel parameter is used, and dmesg | grep PAT.

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.

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  
markus@x4 linux % cat /proc/cpuinfo| grep pat
flags           : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush mmx fxsr sse sse2 ht syscall nx mmxext fxsr_opt pdpe1gb rdtscp lm 3dnowext 3dnow constant_tsc rep_good nopl nonstop_tsc extd_apicid pni monitor cx16 popcnt lahf_lm cmp_legacy svm extapic cr8_legacy abm sse4a misalignsse 3dnowprefetch osvw ibs skinit wdt hw_pstate npt lbrv svm_lock nrip_save vmmcall
...

-- 
Markus