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[Xen-devel] Re: Early test for 32- vs 64-bit hvm domain?

On 30/1/08 18:44, "Andi Kleen" <andi@xxxxxxxxxxxxxx> wrote:

>> As sson as you see LME bit get set in the EFER MSR then you know you have a
>> 64-bit guest. Writes to EFER are emulated in long_mode_do_msr_write() in
>> vmx.c and svm.c. Those are the places to patch in Xen 3.1 branch.
> You could do it slightly earlier by intercepting bios int 0x15 eax=0xec00
> ebx=2 The kernel issues that to tell the BIOS it is 64bit.
> That will only work if the boot loader does not skip the real mode code
> (a few do) 

Oh, I hadn't read about that. We should probably make that call during Xen
boot then. For this particular issue I expect that trapping EFER.LME is
equally good, and it depends on whether the trap is more conveniently
triggered in the hypervisor itself or in the virtual bios.

 -- Keir

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