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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

[..]

  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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