From: Halil Pasic <pasic@linux.ibm.com>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: "Toke Høiland-Jørgensen" <toke@toke.dk>,
"Robin Murphy" <robin.murphy@arm.com>,
"Christoph Hellwig" <hch@lst.de>,
"Maxime Bizon" <mbizon@freebox.fr>,
"Oleksandr Natalenko" <oleksandr@natalenko.name>,
"Marek Szyprowski" <m.szyprowski@samsung.com>,
"Kalle Valo" <kvalo@kernel.org>,
"David S. Miller" <davem@davemloft.net>,
"Jakub Kicinski" <kuba@kernel.org>,
"Paolo Abeni" <pabeni@redhat.com>,
"Olha Cherevyk" <olha.cherevyk@gmail.com>,
iommu <iommu@lists.linux-foundation.org>,
linux-wireless <linux-wireless@vger.kernel.org>,
Netdev <netdev@vger.kernel.org>,
"Linux Kernel Mailing List" <linux-kernel@vger.kernel.org>,
"Greg Kroah-Hartman" <gregkh@linuxfoundation.org>,
stable <stable@vger.kernel.org>,
"Halil Pasic" <pasic@linux.ibm.com>
Subject: Re: [REGRESSION] Recent swiotlb DMA_FROM_DEVICE fixes break ath9k-based AP
Date: Mon, 28 Mar 2022 14:02:04 +0200 [thread overview]
Message-ID: <20220328140205.59c2c1b8.pasic@linux.ibm.com> (raw)
In-Reply-To: <CAHk-=whK3z5O4G55cOb2JYgwisb4cpDK=qhM=0CfmCC8PD+xMQ@mail.gmail.com>
On Sun, 27 Mar 2022 17:30:01 -0700
Linus Torvalds <torvalds@linux-foundation.org> wrote:
> On Sun, Mar 27, 2022 at 4:52 PM Halil Pasic <pasic@linux.ibm.com> wrote:
> >
> > I have no intention of pursuing this. When fixing the information leak,
> > I happened to realize, that a somewhat similar situation can emerge when
> > mappings are reused. It seemed like an easy fix, so I asked the swiotlb
> > maintainers, and they agreed. It ain't my field of expertise, and the
> > drivers I'm interested in don't need this functionality.
>
> Ok.
>
> That said, I think you are putting yourself down when you said in an
> earlier email that you aren't veryt knowledgeable in this area.
>
> I think the fact that you *did* think of this other similar situation
> is actually very interesting, and it's something people probably
> _haven't_ been thinking about.
Thank you!
>
> So I think your first commit fixes the straightforward and common case
> where you do that "map / partial dma / unmap" case.
>
> And that straightforward case is probably all that the disk IO case
> ever really triggers, which is presumably why those "drivers I'm
> interested in don't need this functionality" don't need anything else?
>
I agree.
> And yes, your second commit didn't work, but hey, whatever. The whole
> "multiple operations on the same double buffering allocation"
> situation is something I don't think people have necessarily thought
> about enough.
>
> And by that I don't mean you. I mean very much the whole history of
> our dma mapping code.
>
I agree. We are in the process of catching up! :) My idea was to aid
a process, as a relatively naive pair of eyes: somebody didn't read any
data sheets describing non-cache-coherent DMA, and never programmed
a DMA. It is a fairly common problem, that for the very knowledgeable
certain things seem obvious, self-explanatory or trivial, but for the
less knowledgeable the are not. And knowledge can create bias.
> I then get opinionated and probably too forceful, but please don't
> take it as being about you - it's about just my frustration with that
> code - and if it comes off too negative then please accept my
> apologies.
I have to admit, I did feel a little uncomfortable, and I did look for
an exit strategy. I do believe, that people in your position do have to
occasionally get forceful, and even abrasive to maintain efficiency. I
try to not ignore the social aspect of things, but I do get carried away
occasionally.
Your last especially paragraph is very encouraging and welcome. Thank
you!
Regards,
Halil
[..]
next prev parent reply other threads:[~2022-03-28 12:02 UTC|newest]
Thread overview: 68+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-03-23 7:19 [REGRESSION] Recent swiotlb DMA_FROM_DEVICE fixes break ath9k-based AP Oleksandr Natalenko
2022-03-23 7:28 ` Kalle Valo
2022-03-23 17:27 ` Linus Torvalds
2022-03-23 19:06 ` Robin Murphy
2022-03-23 19:16 ` Linus Torvalds
2022-03-23 20:54 ` Robin Murphy
2022-03-24 5:57 ` Christoph Hellwig
2022-03-24 10:25 ` Oleksandr Natalenko
2022-03-24 11:05 ` Robin Murphy
2022-03-24 14:27 ` Toke Høiland-Jørgensen
2022-03-24 16:29 ` Maxime Bizon
2022-03-24 16:31 ` Christoph Hellwig
2022-03-24 16:52 ` Robin Murphy
2022-03-24 17:07 ` Toke Høiland-Jørgensen
2022-03-24 19:26 ` Linus Torvalds
2022-03-24 21:14 ` Toke Høiland-Jørgensen
2022-03-25 10:25 ` Maxime Bizon
2022-03-25 11:27 ` Robin Murphy
2022-03-25 23:38 ` Halil Pasic
2022-03-26 16:05 ` Toke Høiland-Jørgensen
2022-03-26 18:38 ` Linus Torvalds
2022-03-26 22:38 ` David Laight
2022-03-26 22:41 ` Linus Torvalds
2022-03-25 16:25 ` Toke Høiland-Jørgensen
2022-03-25 16:45 ` Robin Murphy
2022-03-25 18:13 ` Toke Høiland-Jørgensen
2022-03-25 18:30 ` Linus Torvalds
2022-03-25 19:14 ` Robin Murphy
2022-03-25 19:21 ` Linus Torvalds
2022-03-25 19:26 ` Oleksandr Natalenko
2022-03-25 19:27 ` Linus Torvalds
2022-03-25 19:35 ` Oleksandr Natalenko
2022-03-25 20:37 ` Johannes Berg
2022-03-25 20:47 ` Linus Torvalds
2022-03-25 21:13 ` Johannes Berg
2022-03-25 21:40 ` David Laight
2022-03-25 21:56 ` Linus Torvalds
2022-03-25 22:41 ` David Laight
2022-03-27 3:15 ` Halil Pasic
2022-03-28 9:48 ` Johannes Berg
2022-03-28 9:50 ` Johannes Berg
2022-03-28 9:57 ` Johannes Berg
2022-03-27 3:48 ` Halil Pasic
2022-03-27 5:06 ` Linus Torvalds
2022-03-27 5:21 ` Linus Torvalds
2022-03-27 15:24 ` David Laight
2022-03-27 19:23 ` Linus Torvalds
2022-03-27 20:04 ` Linus Torvalds
2022-03-27 23:52 ` Halil Pasic
2022-03-28 0:30 ` Linus Torvalds
2022-03-28 12:02 ` Halil Pasic [this message]
2022-03-27 23:37 ` Halil Pasic
2022-03-28 0:37 ` Linus Torvalds
2022-03-25 7:12 ` Oleksandr Natalenko
2022-03-25 9:21 ` Thorsten Leemhuis
2022-03-24 18:31 ` Halil Pasic
2022-03-25 16:31 ` Christoph Hellwig
2022-03-24 18:02 ` Halil Pasic
2022-03-25 15:25 ` Halil Pasic
2022-03-25 16:23 ` Robin Murphy
2022-03-25 16:32 ` Christoph Hellwig
2022-03-25 18:15 ` Toke Høiland-Jørgensen
2022-03-25 18:42 ` Robin Murphy
2022-03-25 18:46 ` Linus Torvalds
2022-03-28 6:37 ` Christoph Hellwig
2022-03-28 8:15 ` David Laight
2022-03-30 12:11 ` Halil Pasic
2022-03-24 8:55 ` Oleksandr Natalenko
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