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

[Borislav Petkov]

On Thu, Jun 15, 2017 at 09:59:45AM -0500, Tom Lendacky wrote:
> Actually the detection routine, amd_iommu_detect(), is part of the
> IOMMU_INIT_FINISH macro support which is called early through mm_init()
> from start_kernel() and that routine is called before init_amd().

Ah, we do that there too:

	for (p = __iommu_table; p < __iommu_table_end; p++) {

Can't say that that code with the special section and whatnot is
obvious. :-\

Oh, well, early_init_amd() then. That is called in
start_kernel->setup_arch->early_cpu_init and thus before mm_init().

> > If so, it did work fine until now, without the volatile. Why is it
> > needed now, all of a sudden?
> 
> If you run checkpatch against the whole amd_iommu.c file you'll see that

I'm, of course, not talking about the signature change: I'm *actually*
questioning the need to make this argument volatile, all of a sudden.

If there's a need, please explain why. It worked fine until now. If it
didn't, we would've seen it.

If it is a bug, then it needs a proper explanation, a *separate* patch
and so on. But not like now, a drive-by change in an IOMMU enablement
patch.

If it is wrong, then wait_on_sem() needs to be fixed too. AFAICT,
wait_on_sem() gets called in both cases with interrupts disabled, while
holding a lock so I'd like to pls know why, even in that case, does this
variable need to be volatile.

-- 
Regards/Gruss,
    Boris.

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