Re: [PATCH v3] powerpc/pseries/svm: Allocate SWIOTLB buffer anywhere in memory

On Tue, Aug 18, 2020 at 07:11:26PM -0300, Thiago Jung Bauermann wrote:

POWER secure guests (i.e., guests which use the Protection Execution
Facility) need to use SWIOTLB to be able to do I/O with the hypervisor, but
they don't need the SWIOTLB memory to be in low addresses since the
hypervisor doesn't have any addressing limitation.

This solves a SWIOTLB initialization problem we are seeing in secure guests
with 128 GB of RAM: they are configured with 4 GB of crashkernel reserved
memory, which leaves no space for SWIOTLB in low addresses.

To do this, we use mostly the same code as swiotlb_init(), but allocate the
buffer using memblock_alloc() instead of memblock_alloc_low().

Signed-off-by: Thiago Jung Bauermann <redacted>

Looks fine to me (except for the pointlessly long comment lines, but I've
been told that's the powerpc way).