On 06/08/2016 05:07 AM, Matt Fleming wrote:

(Sorry for the delay)

No worries, thanks for all the feedback.

On Thu, 26 May, at 08:45:58AM, Tom Lendacky wrote:

quoted

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.

There are semantics attached to early_ioremap() that do not apply in
this case; that you're mapping an MMIO region but for EFI we just care
about noting where the firmware (not the kernel) populated the region
with data. Similar problems exist for other early boot code such as
the devicetree stuff.

early_ioremap() is not the answer.

What you really want is just some way to distinguish kernel-owned
regions from those owned by "somebody else".

I have no problem updating early_memremap() to take a @flags argument
to make that distinction, provided that the naming is generic and not
tied to AMD's SME technology via an "sme" prefix/suffix.

So maybe something along the lines of an enum that would have entries
(initially) like KERNEL_DATA (equal to zero) and EFI_DATA. Others could
be added later as needed.

Would you then want to allow the protection attributes to be updated
by architecture specific code through something like a __weak function?
In the x86 case I can add this function as a non-SME specific function
that would initially just have the SME-related mask modification in it.

Thanks,
Tom

And making it generic should allow it to be easily sprinkled into the
shared architecture code in drivers/firmware/efi/ without issue.

I'm going to follow up with some additional comments/questions on
PATCH 10.

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