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

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [day] [month] [year] [list]

Message-ID: <4e24113d-b32e-40fd-baa2-0b878b9a7a15@kernel.dk>
Date: Fri, 14 Nov 2025 05:08:59 -0700
From: Jens Axboe <axboe@...nel.dk>
To: Leon Romanovsky <leon@...nel.org>
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 11/14/25 1:16 AM, Leon Romanovsky wrote:
> 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

Distros tend to enable everything under the sun, that's hardly news or
surprising to anyone. And also why the usual arguments of "oh but it
only bloats foo or slows down bar when enabled" are utterly bogus.

But I sure as hell don't run a distro config on my vm or my test boxes,
or anything else I use for that matter, if it's not running a distro
kernel.

-- 
Jens Axboe