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

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Message-ID: <20251114081623.GB147495@unreal>
Date: Fri, 14 Nov 2025 10:16:23 +0200
From: Leon Romanovsky <leon@...nel.org>
To: Jens Axboe <axboe@...nel.dk>
Cc: Keith Busch <kbusch@...nel.org>, Christoph Hellwig <hch@....de>,
	Sagi Grimberg <sagi@...mberg.me>, 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 Thu, Nov 13, 2025 at 01:40:50PM -0700, Jens Axboe wrote:
> 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 :-)

It depends how you are declaring normal people :).
In my Fedora OS, installed on my laptop, CONFIG_PCI_P2PDMA is enabled by default.
https://src.fedoraproject.org/rpms/kernel/blob/rawhide/f/kernel-x86_64-fedora.config#_5567
and in RHEL too
https://src.fedoraproject.org/rpms/kernel/blob/rawhide/f/kernel-x86_64-rhel.config#_4964

Thanks