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

[Thiago Jung Bauermann <bauerman@linux.ibm.com>]

Hello Christoph,

Christoph Hellwig <hch@lst.de> writes:

> On Sat, Aug 15, 2020 at 05:45:36PM -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.
>
> 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