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

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Message-ID: <877dtuhxpo.fsf@mpe.ellerman.id.au>
Date:   Thu, 20 Aug 2020 12:12:35 +1000
From:   Michael Ellerman <mpe@...erman.id.au>
To:     Christoph Hellwig <hch@....de>,
        Thiago Jung Bauermann <bauerman@...ux.ibm.com>
Cc:     iommu@...ts.linux-foundation.org, linuxppc-dev@...ts.ozlabs.org,
        linux-kernel@...r.kernel.org,
        Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
        Christoph Hellwig <hch@....de>,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        Robin Murphy <robin.murphy@....com>,
        Ram Pai <linuxram@...ibm.com>,
        Satheesh Rajendran <sathnaga@...ux.vnet.ibm.com>
Subject: Re: [PATCH v3] powerpc/pseries/svm: Allocate SWIOTLB buffer anywhere in memory

Christoph Hellwig <hch@....de> writes:
> 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 <bauerman@...ux.ibm.com>
>
> Looks fine to me (except for the pointlessly long comment lines, but I've
> been told that's the powerpc way).

They're 80 columns AFAICS?

cheers