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

["Nakajima, Jun" <jun.nakajima@xxxxxxxxx>]

Jerone Young wrote:
> 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:
To me this is consistent with what Andi said.

On some early stepping of processors where NX/XD is _not_ supported at
all, the bit 63 is "Reserved" and ignored. But I don't think CPUID
should tell that NX/XD is supported there in the first place.

Jun
---
Intel Open Source Technology Center

> 
> 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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>> http://lists.xensource.com/xen-devel


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