linux-kernel - Re: [PATCH v4 0/2] block: Enable proper MMIO memory handling for P2P DMA

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Message-ID: <d1641814-5ef8-4ccd-8a41-42bf99a61d0d@kernel.dk>
Date: Thu, 13 Nov 2025 13:40:50 -0700
From: Jens Axboe <axboe@...nel.dk>
To: Keith Busch <kbusch@...nel.org>
Cc: Christoph Hellwig <hch@....de>, Sagi Grimberg <sagi@...mberg.me>,
 Leon Romanovsky <leon@...nel.org>, linux-block@...r.kernel.org,
 linux-kernel@...r.kernel.org, linux-nvme@...ts.infradead.org
Subject: Re: [PATCH v4 0/2] block: Enable proper MMIO memory handling for P2P
 DMA

On 11/13/25 12:52 PM, Keith Busch wrote:
> On Thu, Nov 13, 2025 at 10:45:53AM -0700, Jens Axboe wrote:
>> I took a look, and what happens here is that iter.p2pdma.map is 0 as it
>> never got set to anything. That is the same as PCI_P2PDMA_MAP_UNKNOWN,
>> and hence we just end up in a BLK_STS_RESOURCE. First of all, returning
>> BLK_STS_RESOURCE for that seems... highly suspicious. That should surely
>> be a fatal error. And secondly, this just further backs up that there's
>> ZERO testing done on this patchset at all. WTF?
>>
>> FWIW, the below makes it boot just fine, as expected, as a default zero
>> filled iter then matches the UNKNOWN case.
> 
> I think this must mean you don't have CONFIG_PCI_P2PDMA enabled. The

Right, like most normal people :-)

> state is never set in that case, but I think it should have been.

If you want the patchset to boot, yes it should have been...

-- 
Jens Axboe