linux-kernel - Re: [PATCH 1/1] powerpc/pseries/iommu: Fix window size for direct mapping with pmem

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Message-ID: <2977fdf112bce230ca6739c0a7f9f1f55bd2f693.camel@gmail.com>
Date:   Tue, 20 Apr 2021 02:29:38 -0300
From:   Leonardo Bras <leobras.c@...il.com>
To:     Alexey Kardashevskiy <aik@...abs.ru>,
        Michael Ellerman <mpe@...erman.id.au>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>
Cc:     linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/1] powerpc/pseries/iommu: Fix window size for direct
 mapping with pmem

On Tue, 2021-04-20 at 15:18 +1000, Alexey Kardashevskiy wrote:
> 
> On 20/04/2021 14:54, Leonardo Bras wrote:
> > As of today, if the DDW is big enough to fit (1 << MAX_PHYSMEM_BITS) it's
> > possible to use direct DMA mapping even with pmem region.
> > 
> > But, if that happens, the window size (len) is set to
> > (MAX_PHYSMEM_BITS - page_shift) instead of MAX_PHYSMEM_BITS, causing a
> > pagesize times smaller DDW to be created, being insufficient for correct
> > usage.
> > 
> > Fix this so the correct window size is used in this case.
> 
> Good find indeed.
> 
> afaict this does not create a huge problem though as 
> query.largest_available_block is always smaller than (MAX_PHYSMEM_BITS - 
> page_shift) where it matters (phyp).
> 
> 
> Reviewed-by: Alexey Kardashevskiy <aik@...abs.ru>
> 

Thanks for reviewing!

Leonardo Bras