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

On 30/1/08 00:34, "Dan Magenheimer" <dan.magenheimer@xxxxxxxxxx> wrote:

>> As long as e.g. Linux has not started (i.e. during bios and grub for
>> instance), you can't know whether that will be a 64bit Linux
>> or a 32bit
>> Linux.
> That's what I was afraid of...
> Then what is the earliest point in the execution of an x86_64
> domain/vcpu in *xen* where hvm_long_mode_enabled(v) will work
> properly? E.g. in Linux/x86_64 is long mode set early in __start?
> And is this done via a hypercall or an emulated instruction?

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.

 -- Keir

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