Re: [PATCH v7 07/36] x86/mm: Don't use phys_to_virt in ioremap() if SME is active

[Tom Lendacky]

On 6/20/2017 3:55 PM, Thomas Gleixner wrote:
> On Fri, 16 Jun 2017, Tom Lendacky wrote:
>
> > Currently there is a check if the address being mapped is in the ISA
> > range (is_ISA_range()), and if it is then phys_to_virt() is used to
> > perform the mapping.  When SME is active, however, this will result
> > in the mapping having the encryption bit set when it is expected that
> > an ioremap() should not have the encryption bit set. So only use the
> > phys_to_virt() function if SME is not active
>
> This does not make sense to me. What the heck has phys_to_virt() to do with
> the encryption bit. Especially why would the encryption bit be set on that
> mapping in the first place?

The default is that all entries that get added to the pagetables have
the encryption bit set unless specifically overridden.  Any __va() or
phys_to_virt() calls will result in a pagetable mapping that has the
encryption bit set.  For ioremap, the PAGE_KERNEL_IO protection is used
which will not/does not have the encryption bit set.

> I'm probably missing something, but this want's some coherent explanation
> understandable by mere mortals both in the changelog and the code comment.

I'll add some additional info to the changelog and code.

Thanks,
Tom

> Thanks,
>
> 	tglx