Re: [PATCH 4/4] x86, efi: Map runtime services 1:1

H. Peter Anvin
2013-06-06T19:38:10Z

On 06/06/2013 12:36 PM, Borislav Petkov wrote:
> On Thu, Jun 06, 2013 at 12:28:20PM -0700, H. Peter Anvin wrote:
>> Or we could materialize mappings for this specific PGD. However,
>> adding a read of %cr3 in __do_page_fault sounds expensive.
>
> Yes, I think we want to make sure all mappings are there when we do an
> EFI runtime call so that we never #PF while it executes.
>
> Matt mentioned on IRC that the it could be that his EFI runtime is
> referencing EFI_RESERVED area which we don't map. However, we need to
> confirm/disprove that first, as it is currently only a hunch.

If it is true, then maybe a #PF handler which materializes mappings on
demand might be the right thing to do.

Again, it would be interesting to stop a WinX VM in the process of doing
an EFI call and see exactly what it has set up in its page tables.

-hpa