Re: [RFC PATCH v1 10/18] x86/efi: Access EFI related tables in the clear

[Tom Lendacky]

On 05/25/2016 02:30 PM, Matt Fleming wrote:
> On Tue, 24 May, at 09:54:31AM, Tom Lendacky wrote:
>>
>> I looked into this and this would be a large change also to parse tables
>> and build lists.  It occurred to me that this could all be taken care of
>> if the early_memremap calls were changed to early_ioremap calls. Looking
>> in the git log I see that they were originally early_ioremap calls but
>> were changed to early_memremap calls with this commit:
>>
>> commit abc93f8eb6e4 ("efi: Use early_mem*() instead of early_io*()")
>>
>> Looking at the early_memremap code and the early_ioremap code they both
>> call __early_ioremap so I don't see how this change makes any
>> difference (especially since FIXMAP_PAGE_NORMAL and FIXMAP_PAGE_IO are
>> identical in this case).
>>
>> Is it safe to change these back to early_ioremap calls (at least on
>> x86)?
> 
> I really don't want to begin mixing early_ioremap() calls and
> early_memremap() calls for any of the EFI code if it can be avoided.

I definitely wouldn't mix them, it would be all or nothing.

> 
> There is slow but steady progress to move more and more of the
> architecture specific EFI code out into generic code. Swapping
> early_memremap() for early_ioremap() would be a step backwards,
> because FIXMAP_PAGE_NORMAL and FIXMAP_PAGE_IO are not identical on
> ARM/arm64.

Maybe adding something similar to __acpi_map_table would be more
appropriate?

> 
> Could you point me at the patch that in this series that fixes up
> early_ioremap() to work with mem encrypt/decrypt? I took another
> (quick) look through but couldn't find it.

The patch in question is patch 6/18 where PAGE_KERNEL is changed to
include the _PAGE_ENC attribute (the encryption mask). This now
makes FIXMAP_PAGE_NORMAL contain the encryption mask while
FIXMAP_PAGE_IO does not. In this way, anything mapped using the
early_ioremap call won't be mapped encrypted.

Thanks,
Tom

>