Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
Message-ID: <2977fdf112bce230ca6739c0a7f9f1f55bd2f693.camel@gmail.com>
Subject: Re: [PATCH 1/1] powerpc/pseries/iommu: Fix window size for direct
 mapping with pmem
From:   Leonardo Bras <leobras.c@gmail.com>
To:     Alexey Kardashevskiy <aik@ozlabs.ru>,
        Michael Ellerman <mpe@ellerman.id.au>,
        Benjamin Herrenschmidt <benh@kernel.crashing.org>,
        Paul Mackerras <paulus@samba.org>
Cc:     linuxppc-dev@lists.ozlabs.org, linux-kernel@vger.kernel.org
Date:   Tue, 20 Apr 2021 02:29:38 -0300
In-Reply-To: <58b28a98-37aa-055f-5dec-d8c0005c9519@ozlabs.ru>
References: <20210420045404.438735-1-leobras.c@gmail.com>
         <58b28a98-37aa-055f-5dec-d8c0005c9519@ozlabs.ru>
Organization: IBM
Content-Type: text/plain; charset="UTF-8"
User-Agent: Evolution 3.38.4 (3.38.4-1.fc33) 
MIME-Version: 1.0
Content-Transfer-Encoding: 7bit
Precedence: bulk

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@ozlabs.ru>
> 

Thanks for reviewing!

Leonardo Bras