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


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