Nakajima, Jun
2005-Aug-18 16:16 UTC
RE: [Xen-devel] Re: [PATCH] supporting non-NX/XD capableprocessors on x86_64 xenlinux
Jerone Young wrote:> On Thu, 2005-08-18 at 17:51 +0200, Andi Kleen wrote: >> Keir Fraser <Keir.Fraser@cl.cam.ac.uk> 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 >> >> _______________________________________________ >> Xen-devel mailing list >> Xen-devel@lists.xensource.com >> http://lists.xensource.com/xen-devel_______________________________________________ Xen-devel mailing list Xen-devel@lists.xensource.com http://lists.xensource.com/xen-devel