Re: [Xen-devel] Re: [PATCH] supporting non-NX/XD capable processors on x86_64 xenlinux

[Jerone Young <jyoung5@xxxxxxxxxx>]

On Thu, 2005-08-18 at 17:51 +0200, Andi Kleen wrote:
> Keir Fraser <Keir.Fraser@xxxxxxxxxxxx> writes:
> > 
> > By the way -- from what I've seen of this NX/XD discussion so far, it
> > sounds like even if CPUID says that NX/XD is supported, and you set
> > the EFER.NXE bit, the BIOS can still cause this to be ignored! Is this
> > true and, if so, what will happen if you try to use NX/XD anyway?
> > i.e., will the bit be ignored, or will its use cause a page fault?
> 
> I don't think that can happen. When NX is disabled or not there it
> doesn't appear in CPUID.

Ah but it does:

With NX bit cut "on" in bios:
/proc/cpuinfo
processor       : 0
vendor_id       : GenuineIntel
cpu family      : 15
model           : 4
model name      :                   Intel(R) Xeon(TM) CPU 3.20GHz
stepping        : 1
cpu MHz         : 800.028
cache size      : 1024 KB
physical id     : 0
siblings        : 2
core id         : 0
cpu cores       : 1
fpu             : yes
fpu_exception   : yes
cpuid level     : 5
wp              : yes
flags           : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge
mca cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm syscall
nx lm constant_tsc pni monitor ds_cpl cid cx16 xtpr   <--- NX found here
bogomips        : 6396.31
clflush size    : 64
cache_alignment : 128
address sizes   : 36 bits physical, 48 bits virtual
power management:

With NX bit cut "off" in bios:
cat /proc/cpuinfo
processor       : 0
vendor_id       : GenuineIntel
cpu family      : 15
model           : 4
model name      :                   Intel(R) Xeon(TM) CPU 3.20GHz
stepping        : 1
cpu MHz         : 3200.280
cache size      : 1024 KB
physical id     : 0
siblings        : 2
core id         : 0
cpu cores       : 1
fpu             : yes
fpu_exception   : yes
cpuid level     : 5
wp              : yes
flags           : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge
mca cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm syscall
lm pni monitor ds_cpl cid cmpxchg16b
bogomips        : 6324.22
clflush size    : 64
cache_alignment : 128
address sizes   : 36 bits physical, 48 bits virtual
power management:

Notice no nx in the flags when NX is turned off in the bios. 




> 
> -Andi
> 
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> 
-- 
Jerone Young
IBM Linux Technology Center
jyoung5@xxxxxxxxxx
512-838-1157 (T/L: 678-1157)


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