From: Marcin Wojtas <email@example.com>
To: "Marek Behún" <firstname.lastname@example.org>
Cc: "Russell King (Oracle)" <email@example.com>,
firstname.lastname@example.org, Christoph Hellwig <email@example.com>,
Robin Murphy <firstname.lastname@example.org>,
Arnd Bergmann <email@example.com>,
Andre Przywara <firstname.lastname@example.org>,
Marc Zyngier <email@example.com>,
Linus Torvalds <firstname.lastname@example.org>,
Andrew Lunn <email@example.com>,
Gregory Clement <firstname.lastname@example.org>,
Greg Kroah-Hartman <email@example.com>,
Subject: Re: REGRESSION in 6.0-rc7 caused by patch "ARM/dma-mapping: use dma-direct unconditionally"
Date: Mon, 3 Oct 2022 23:30:31 +0200 [thread overview]
Message-ID: <CAPv3WKcggJ3ki+8DQyA=P=+d714kYxA2-M5xtZf9fEENkk5osQ@mail.gmail.com> (raw)
pon., 3 paź 2022 o 17:33 Marek Behún <firstname.lastname@example.org> napisał(a):
> On Mon, 3 Oct 2022 15:11:44 +0100
> "Russell King (Oracle)" <email@example.com> wrote:
> > On Mon, Oct 03, 2022 at 09:30:37AM +0200, Christoph Hellwig wrote:
> > > On Fri, Sep 30, 2022 at 05:02:05PM +0200, Marek Behún wrote:
> > > > It seems that the null pointer dereference comes from the data variable
> > > > having zero value. We assign
> > > > data = (u8 *)(uintptr_t)rx_desc->buf_cookie;
> > >
> > > I never see any assignment to ->buf_cookie in the driver, what am
> > > I missing?
> > I think Marek's setup (like my setups) use the hardware buffer manager,
> > and it's hardware that fills in the "buf_cookie", which is supposed to
> > be the virtual address of the buffer.
> > Each buffer supplied to the hardware buffer manager is supposed to
> > contain the virtual address in the first 32-bit word in that buffer.
> > This is done by mvneta_bm_construct():
> > /* In order to update buf_cookie field of RX descriptor properly,
> > * BM hardware expects buf virtual address to be placed in the
> > * first four bytes of mapped buffer.
> > */
> > *(u32 *)buf = (u32)buf;
> > immediately prior to dma_map_single(..., DMA_FROM_DEVICE) is called.
> > If I had to guess, I would suggest that this write is being lost via
> > cache invalidation, and given that the hardware BM both reads and
> > writes this buffer, DMA_FROM_DEVICE is not correct, it should be
> > DMA_BIDIRECTIONAL.
I think the DMA_FROM_DEVICE is used rather properly in the RX path of
the driver - the CPU doesn't access the payload afterward. The BM only
pushes the pointers back and forth between internal SRAM ('internal
pool' - BPPI) to DRAM ('external pool' - BPPE) and the descriptors,
but afaik it should not touch the buffer contents. But maybe somehow
it affects the coherency and DMA_BIDIRECTIONAL are indeed required...
About the coherency itself - please see my comment below.
Another thought - when writing to *buf (memory normal) shouldn't we add a dsb()?
> > Changing that is probably going to need DMA_FROM_DEVICE also changed
> > elsewhere in the mvneta_bm and mvneta driver.
> > I'm not in a position where I could test that out. Marek?
> Hello Russell,
> thanks for your suggestion!
> Adding Pali, since he has some information (see at the end of this
> The attached patch seems to solve the null-pointer dereference.
Did you manage to measure performance impact?
I have one overall concern here. On all kinds of A38x-based boards I
worked on, by default, the firmware set all devices (e.g. network,
AHCI, XHCI) on MBUS as fully IO cache coherent - it should be
reflected in the MVNETA_WIN_BASE(w) registers attribute field. Bits
[15:8] should be set to 0x1D (or 0x1E if there is a second DRAM CS
used). Can you please try adding 'dma-coherent;' property under the
> I booted into single user mode and enabled eth2. Before it caused the
> NULL pointer dereference after link got up, not it does not happen.
> But I am still encountering the freeze after booting into system.
> Maybe these are different bugs?
> I am thinking whether we don't need something similar like
> 7bea67a99430 ("ARM: dts integrator: Fix DMA ranges")
> also for mvebu.
> I seem to remember Pali talking about how the ranges defined in some
> upstream mvebu-tree, using MBUS_ID() macros, are incorrect.
> Pali, what do you remember about this?
Afaik there should be no issues around MBUS configuration for non-PCIE devices.
linux-arm-kernel mailing list
next prev parent reply other threads:[~2022-10-03 21:32 UTC|newest]
Thread overview: 43+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-09-30 13:10 REGRESSION in 6.0-rc7 caused by patch "ARM/dma-mapping: use dma-direct unconditionally" Marek Behún
2022-09-30 13:46 ` Robin Murphy
2022-09-30 14:52 ` Marek Behún
2022-09-30 15:02 ` Marek Behún
2022-09-30 16:41 ` Robin Murphy
2022-09-30 18:02 ` Marek Behún
2022-10-03 7:21 ` Christoph Hellwig
2022-10-03 7:30 ` Christoph Hellwig
2022-10-03 14:11 ` Russell King (Oracle)
2022-10-03 15:25 ` Marek Behún
2022-10-03 16:09 ` Pali Rohár
2022-10-03 19:04 ` Marek Behún
2022-10-03 19:08 ` Pali Rohár
2022-10-03 21:30 ` Marcin Wojtas [this message]
2022-10-03 21:35 ` Pali Rohár
2022-10-03 22:03 ` Marcin Wojtas
2022-10-04 7:10 ` Christoph Hellwig
2022-10-04 8:15 ` Marek Behún
2022-10-04 8:17 ` [PATCH] ARM: mvebu: select OF_DMA_DEFAULT_COHERENT if MACH_MVEBU_V7 Marek Behún
2022-10-04 8:30 ` Christoph Hellwig
2022-10-04 12:54 ` Marek Behún
2022-10-04 8:30 ` Arnd Bergmann
2022-10-04 9:14 ` Thorsten Leemhuis
2022-10-04 9:22 ` Russell King (Oracle)
2022-10-04 9:56 ` REGRESSION in 6.0-rc7 caused by patch "ARM/dma-mapping: use dma-direct unconditionally" Robin Murphy
2022-10-04 7:25 ` Russell King (Oracle)
2022-10-04 8:30 ` Marcin Wojtas
2022-10-04 9:08 ` Russell King (Oracle)
2022-10-04 12:36 ` Marek Behún
2022-10-04 12:59 ` Marcin Wojtas
2022-10-04 18:51 ` Pali Rohár
2022-10-04 19:35 ` Marcin Wojtas
2022-10-04 8:26 ` Marek Behún
2022-10-04 8:36 ` Marcin Wojtas
2022-10-20 18:22 ` Russell King (Oracle)
2022-10-20 19:10 ` Marek Behún
2022-10-21 16:25 ` Linus Torvalds
2022-10-21 16:30 ` Christoph Hellwig
2022-10-21 18:21 ` Russell King (Oracle)
2022-10-23 11:58 ` Klaus Kudielka
2022-10-03 18:57 ` Marek Behún
2022-10-01 9:31 ` Thorsten Leemhuis
2022-11-04 12:08 ` REGRESSION in 6.0-rc7 caused by patch "ARM/dma-mapping: use dma-direct unconditionally" #forregzbot Thorsten Leemhuis
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