Re: [PATCH v6 26/34] iommu/amd: Allow the AMD IOMMU to work with memory encryption

[Borislav Petkov]

On Wed, Jun 14, 2017 at 03:40:28PM -0500, Tom Lendacky wrote:
> I was trying to keep all the logic for it here in the SME related files
> rather than put it in the iommu code itself. But it is easy enough to
> move if you think it's worth it.

Yes please - the less needlessly global symbols, the better.

> > Also, you said in another mail on this subthread that c->microcode
> > is not yet set. Are you saying, that the iommu init gunk runs before
> > init_amd(), where we do set c->microcode?
> > 
> > If so, we can move the setting to early_init_amd() or so.
> 
> I'll look into that.

And I don't think c->microcode is not set by the time we init the iommu
because, AFAICT, we do the latter in pci_iommu_init() and that's a
rootfs_initcall() which happens later then the CPU init stuff.

> I'll look into simplifying the checks.

Something like this maybe?

	if (rev >= 0x1205)
		return true;

	if (rev <= 0x11ff && rev >= 0x1126)
		return true;

	return false;

> > WARNING: Use of volatile is usually wrong: see Documentation/process/volatile-considered-harmful.rst
> > #134: FILE: drivers/iommu/amd_iommu.c:866:
> > +static void build_completion_wait(struct iommu_cmd *cmd, volatile u64 *sem)
> > 
> 
> The semaphore area is written to by the device so the use of volatile is
> appropriate in this case.

Do you mean this is like the last exception case in that document above:

"
  - Pointers to data structures in coherent memory which might be modified
    by I/O devices can, sometimes, legitimately be volatile.  A ring buffer
    used by a network adapter, where that adapter changes pointers to
    indicate which descriptors have been processed, is an example of this
    type of situation."

?

If so, it did work fine until now, without the volatile. Why is it
needed now, all of a sudden?

-- 
Regards/Gruss,
    Boris.

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