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

From: Daniel Kiper
Date: Wed May 25 2016 - 12:11:07 EST

On Tue, May 24, 2016 at 09:54:31AM -0500, Tom Lendacky wrote:
> On 05/12/2016 01:20 PM, Tom Lendacky wrote:
> > On 05/10/2016 08:57 AM, Borislav Petkov wrote:
> >> On Tue, May 10, 2016 at 02:43:58PM +0100, Matt Fleming wrote:
> >>> Is it not possible to maintain some kind of kernel virtual address
> >>> mapping so memremap*() and friends can figure out when to twiddle the
> >>> mapping attributes and map with/without encryption?
> >>
> >> I guess we can move the sme_* specific stuff one indirection layer
> >> below, i.e., in the *memremap() routines so that callers don't have to
> >> care... That should keep the churn down...
> >>
> >
> > We could do that, but we'll have to generate that list of addresses so
> > that it can be checked against the range being mapped. Since this is
> > part of early memmap support searching that list every time might not be
> > too bad. I'll have to look into that and see what that looks like.
> 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)?

Commit f955371ca9d3986bca100666041fcfa9b6d21962 (x86: remove the Xen-specific
_PAGE_IOMAP PTE flag) made commit abc93f8eb6e4 unnecessary. Though, IMO, it
is still valid code cleanup. So, if it is not very strongly needed I would
not revert this change.