Re: port-i386/52266: Double fault early in boot with Transmeta Crusoe CPU

[Kimihiro Nonaka <nonakap%gmail.com@localhost>]

The following reply was made to PR port-i386/52266; it has been noted by GNATS.

From: Kimihiro Nonaka <nonakap%gmail.com@localhost>
To: "gnats-bugs%netbsd.org@localhost" <gnats-bugs%netbsd.org@localhost>
Cc: NONAKA Kimihiro <nonaka%netbsd.org@localhost>, "gnats-admin%netbsd.org@localhost" <gnats-admin%netbsd.org@localhost>, 
	"netbsd-bugs%netbsd.org@localhost" <netbsd-bugs%netbsd.org@localhost>, Andreas Gustafsson <gson%gson.org@localhost>
Subject: Re: port-i386/52266: Double fault early in boot with Transmeta Crusoe CPU
Date: Sat, 8 Jul 2017 20:06:04 +0900

 Hi,
 
 2017-07-08 18:15 GMT+09:00 Simon Burge <simonb%netbsd.org@localhost>:
 
 >  If I change lapic_is_x2apic() to unconditionally return false, my
 >  Soekris boots (at least to single user mode).
 >
 >  I tried to get lapic_is_x2apic() to store the value of the MSR it
 >  reads by changing that function to:
 >
 >         uint64_t x2apic_msr;
 >
 >         bool
 >         lapic_is_x2apic(void)
 >         {
 >                 x2apic_msr = rdmsr(MSR_APICBASE);
 >                 return false;
 >         }
 >
 >  but that just faulted/paniced too, but slightly differently:
 >
 >         > boot net8 -s
 >         17730720+696076+839124 [776736+802655]=0x13e1cbc
 >         fatal protection faufatal double fault in supervisor mode
 >         trap type 13 code 0xc0118298 eip 0x8 cs 0x246 eflags 0xc054bbf6 cr2 0 ilevel 0x8 esp 0xc11ea760
 >         curlwp 0xc125f360 pid 0 lid 1 lowest kstack 0xc14e32c0
 >         kernel: user trap double fault, code=0
 >         Stopped in pid 0.1 (system) at  8:      invalid address
 >         db{0}>
 >
 >  The chopped off "fatal protection fau" is new.  Could the rdmsr() itself
 >  be faulting then??
 >
 >  Is there any further info I get to help?
 
 Could you try the following patch.
 
 diff --git a/sys/arch/x86/x86/lapic.c b/sys/arch/x86/x86/lapic.c
 index 20822a67184..372e9f8c0c2 100644
 --- a/sys/arch/x86/x86/lapic.c
 +++ b/sys/arch/x86/x86/lapic.c
 @@ -235,10 +235,12 @@ lapic_enable_x2apic(void)
  bool
  lapic_is_x2apic(void)
  {
 -    uint64_t r;
 +    uint64_t msr;
 
 -    r = rdmsr(MSR_APICBASE);
 -    return (r & (APICBASE_EN | APICBASE_EXTD)) == (APICBASE_EN |
 APICBASE_EXTD);
 +    if (rdmsr_safe(MSR_APICBASE, &msr) == EFAULT)
 +        return false;
 +    return (msr & (APICBASE_EN | APICBASE_EXTD)) ==
 +        (APICBASE_EN | APICBASE_EXTD);
  }
 
  /*
 
 
 Regards,
 -- 
 Kimihiro Nonaka