[PATCH v7 00/17] mm, dma, arm64: Reduce ARCH_KMALLOC_MINALIGN to 8

[Frank Li]

On Fri, Mar 28, 2025 at 04:41:05PM +0000, John Ernberg wrote:
> On 6/12/23 5:31 PM, Catalin Marinas wrote:
> > Hi,
> >
> > That's v7 of the series reducing the kmalloc() minimum alignment on
> > arm64 to 8 (from 128). There's no new/different functionality, mostly
> > cosmetic changes and acks/tested-bys.
> >
> > Andrew, if there are no further comments or objections to this version,
> > are you ok to take the series through the mm tree? The arm64 changes are
> > fairly small. Alternatively, I can push it into linux-next now to give
> > it some wider exposure and decide whether to upstream it when the
> > merging window opens. Thanks.
> >
> > The updated patches are also available on this branch:
> >
> > git://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux devel/kmalloc-minalign
> >
>
> (I trimmed the recipients and added linux-usb and imx mailing list, +
> cdns3 maintainers)
>
> Hi Catalin, lists,
>
> Seen on Linux 6.12.20, it is not trivial for us to test later kernels so
> if the issue is potentially fixed we are more than happy to cherry-pick
> the potential fixes and give them a go.
>
> Having an SMSC9512 (smsc95xx) USB Ethernet/Hub chip attached to the armv8
> SoC iMX8QXP over the Cadence USB3 USB2 interface (cdns3-imx) will since
> the patch set at [0] cause random interrupt storms over the SMSC9512 INT
> EP.

Do you know where buy SMSC9512 USB Ethernet/Hub?

>
> The reason for the storm is that the async URBs queued at [1] right before
> the interrupt configuration [2] in the driver.
> With [0] applied, those async URBs are likely clobbering any URB located
> after them in memory somewhere in the xhci memory space.
> The memory corruption only happens if there is more than one URB in the
> queue at the same time, making these async URBs a good trigger of the
> problem.
> If we force those URBs to be sync or use the hack inlined below, the
> problem goes away.
>
> The content of read_buf in the interrupt configuration read at [2] looks
> to be the lo-part of a pointer +-20 bytes distance from the pointers
> present in the async URBs queued from [1] when we dumped the URB structures
> instead of the expected register contents.
>
> Attached are 3 usbmon captures, with some annotations, which we thought
> might contain useful hints.
>
> * usb-annotated-bad.pcapng shows the URB that will get clobbered is queued
>    at position 280, and completes at 282.
>
> * usb-annotated-good.pcapng shows the URB that gets clobbered in the bad
>    case is queued at position 282 and completes at 283.
>
> The above captures are from a kernel where the hack has not been applied.
>
> * usb-annotated-hackfix.pcapng shows the URB that gets clobbered in the
>    bad case is queued at position 238 and completes at 240.

Maillist have not attachment. Can you send it to me directly?

Frank

>
> This was captured after the hack fix inlined below was applied.
>
> We have no reason to believe [0] is actually causing this, but rather
> the improvements uncovered a pre-existing issue with the Cadence 3
> integration in the iMX8QXP, as otherwise USB would be some level of broken
> for absolutely everyone on ARM64 since 2+ years.
>
> The reason we did not notice the issue earlier is that until very recently
> we have been stuck on the NXP vendoring of 6.1 which pre-dates [0].
>
> We determined [0] uncovers the breakage by replacing the host/ and cdns3/
> code with the NXP 6.1 vendor kernel code in a Frankenstein fashion and
> still ending up with the same USB breakage.
>
> Running KASAN on this doesn't trigger anything, so it's not a KASAN
> detectable issue.
>
> Our knowledge on how to progress on debugging this has unfortunately come
> to an end. We'd deeply appreciate any suggestion or possible patches to
> test.
>
> Best regards // John Ernberg
>
> [0]:
> https://lore.kernel.org/linux-mm/20230612153201.554742-1-catalin.marinas@arm.com/
> [1]:
> https://elixir.bootlin.com/linux/v6.12.19/source/drivers/net/usb/smsc95xx.c#L525
> [2]:
> https://elixir.bootlin.com/linux/v6.12.19/source/drivers/net/usb/smsc95xx.c#L1045
>
> ------------------->8-----------
> diff --git a/arch/arm64/include/asm/cache.h b/arch/arm64/include/asm/cache.h
> index 06a4670bdb0b..7356801faa52 100644
> --- a/arch/arm64/include/asm/cache.h
> +++ b/arch/arm64/include/asm/cache.h
> @@ -33,7 +33,7 @@
>    * the CPU.
>    */
>   #define ARCH_DMA_MINALIGN      (128)
> -#define ARCH_KMALLOC_MINALIGN  (8)
> +#define ARCH_KMALLOC_MINALIGN  (128)
>
>   #ifndef __ASSEMBLY__