Re: [Xen-devel] [REBASE] xen: patches (against Linux kernel) for supporting efi

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 23.05.13 at 16:11, Eric Shelton <eshelton@xxxxxxxxx> wrote:
> I see, and I should have caught it from your first comment (although
> my understanding is that EFI ver 1.xx works in addition to UEFI).

Not sure what you're trying to tell me here.

>  It
> sounds like the patch as presented, minus any comments suggesting the
> need for determining if there is a 32-bit EFI, is good on this point,
> since it always sets the EFI_64BIT bit.

Really it should probably set this bit simply cased upon the
CONFIG_64BIT value.

> Just curious: why does Xen only work on 64-bit EFI?  Is there an
> architectural issue, or is 64-bit x86 so overwhelmingly prevalent that
> there are essentially no Xen users running on 32-bit EFI systems?  It
> looks like the Linux kernel bothers to support both 32 and 64 bit EFI,
> but does not support EFI runtime where there is a 32/64 bit mix of
> BIOS & OS (which appears to not be an issue for 64-bit Xen & a 32-bit
> dom0).

First of all, -unstable (which is what will become 4.3) doesn't support
running as 32-bit hypervisor at all anymore.

And then, when 32-bit support was still there, i.e. in 4.2, there was
no support for booting from 32-bit EFI in the code (largely because
at that point it was already clear that any effort to make 32-bit EFI
would be mostly wasted as 32-bit support was going to go away
soon anyway). Plus there was never any demand for booting 32-bit
Xen from EFI according to all I know.

Jan


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