Re: [PATCH] swiotlb: Allow allocating buffer anywhere in memory

Hello Christoph,

Christoph Hellwig [off-list ref] writes:

On Sat, Aug 15, 2020 at 05:45:36PM -0300, Thiago Jung Bauermann wrote:

quoted

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.

What about just open coding the allocation and using
swiotlb_init_with_tbl?

Yes, that works too. I just sent a v2 implementing that change. I just
had to add a small accessor function so that I could set no_iotlb_memory
from outside swiotlb.c.

Thank you for the quick review.

-- 
Thiago Jung Bauermann
IBM Linux Technology Center