Re: [Xen-devel] [PATCH v4 4/5] x86: add multiboot2 protocol support for EFI platforms

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 18.01.17 at 20:51, <andrew.cooper3@xxxxxxxxxx> wrote:
> On 18/01/17 14:17, Doug Goldstein wrote:
>> +.Lefi_multiboot2_proto:
>> +        /* Zero EFI SystemTable and EFI ImageHandle addresses. */
>> +        xor     %esi,%esi
>> +        xor     %edi,%edi
>> +
>> +        /* Skip Multiboot2 information fixed part. */
>> +        lea     (MB2_fixed_sizeof+MULTIBOOT2_TAG_ALIGN-1)(%rbx),%ecx
>> +        and     $~(MULTIBOOT2_TAG_ALIGN-1),%ecx
> 
> Are we strictly guaranteed to have the entire image, including multiboot
> tags, loaded below 4GB virtual even in the 64bit case? Even on non-EFI
> capable grub2's ?

I can't speak for GrUB, but I've recently learned that EFI alone
doesn't appear to make such guarantees, and also doesn't look
to have ways to request such address restricted loading of an
image. Hence there'll be work needed to make at least xen.efi
cope with being loaded above that boundary.

Jan


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