linux-kernel - Re: [PATCH 0/1] swiotlb: Make IO_TLB

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

Message-ID: <824c8fa6acda7c840f856430b5d898c7fcd4702e.camel@siemens.com>
Date: Fri, 25 Apr 2025 05:32:19 +0000
From: "Li, Hua Qian" <HuaQian.Li@...mens.com>
To: "robin.murphy@....com" <robin.murphy@....com>, "m.szyprowski@...sung.com"
	<m.szyprowski@...sung.com>
CC: "Kiszka, Jan" <jan.kiszka@...mens.com>, "iommu@...ts.linux.dev"
	<iommu@...ts.linux.dev>, "Su, Bao Cheng" <baocheng.su@...mens.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 0/1] swiotlb: Make IO_TLB_SEGSIZE Configurable

On Thu, 2025-04-24 at 13:58 +0100, Robin Murphy wrote:
> On 24/04/2025 6:12 am, Li, Hua Qian wrote:
> > On Tue, 2025-04-22 at 15:36 +0200, Marek Szyprowski wrote:
> > > On 22.04.2025 08:37, huaqian.li@...mens.com wrote:
> > > > From: Li Hua Qian <huaqian.li@...mens.com>
> > > >
> > > > This patchset introduces a change to make the IO_TLB_SEGSIZE
> > > > parameter
> > > > configurable via a new kernel configuration option
> > > > (CONFIG_SWIOTLB_SEGSIZE).
> > > >
> > > > In certain applications, the default value of IO_TLB_SEGSIZE
> > > > (128)
> > > > may
> > > > not be sufficient for memory allocation, leading to runtime
> > > > errors.
> > > > By
> > > > making this parameter configurable, users can adjust the
> > > > segment
> > > > size to
> > > > better suit their specific use cases, improving flexibility and
> > > > system
> > > > stability.
> > >
> > > Could You elaborate a bit more what are those certain
> > > applications
> > > that
> > > require increasing IO_TLB_SEGSIZE? I'm not against it, but such
> > > change
> > > should be well justified and described, while the above cover-
> > > letter
> > > doesn't provide anything more than is written in the patch
> > > description.
> > Thank you for your feedback, Marek.
> >
> > To provide more context, one specific application that requires
> > increasing IO_TLB_SEGSIZE is the Hailo 8 PCIe AI card. This card
> > uses
> > dma_alloc_coherent to allocate descriptor lists, as seen in the
> > Hailo
> > driver implementation here:
> > https://github.com/hailo-ai/hailort-drivers/blob/7161f9ee5918029bd4497f590003c2f87ec32507/linux/vdma/memory.c#L322
> > The maximum size (nslots) for these allocations can reach 160,
> > which
> > exceeds the current default value of IO_TLB_SEGSIZE (128).
> >
> > Since IO_TLB_SEGSIZE is defined as a constant in the kernel:
> >
> > `#define IO_TLB_SEGSIZE 128`
> >
> >
> > this limitation causes swiotlb_search_pool_area,
> > https://github.com/torvalds/linux/blame/v6.15-rc2/kernel/dma/swiotlb.c#L1085
> > ,
> > (or swiotlb_do_find_slots in older kernels) to fail when attempting
> > to
> > allocate contiguous physical memory (CMA). This results in runtime
> > errors and prevents the Hailo 8 card from functioning correctly in
> > certain configurations.
>
> Hmm, dma_alloc_coherent() should really not be trying to allocate
> from
> SWIOTLB in the first place - how is that happening?
>
> If you're using restricted DMA for a device which wants significant
> coherent allocations, then it wants to have it's own shared-dma-pool
> for
> those *as well* as the restricted-dma-pool for bouncing streaming
> DMA.
>
> Thanks,
> Robin.

Hi Robin,

Regarding the specific Hailo Card case, the issue arises due
to the capabilities of certain SoCs or CPUs. For example, many
K3 SoCs lack an IOMMU, which is typically used to isolate the
system against DMA-based attacks of external PCI devices.

Taking the TI AM65 as an example, it doesn't have an IOMMU, but
instead includes a Peripheral Virtualization Unit (PVU). The
PVU provides functionality similar to an IOMMU and is used to
isolate PCI devices from the Linux host, and the SWIOTLB is
used to manp all DMA buffers from a static memory carve-out.

You can find more details and background information here:
https://lore.kernel.org/all/20250422061406.112539-1-huaqian.li@siemens.com/

>
> > By making IO_TLB_SEGSIZE configurable via a kernel configuration
> > option
> > (CONFIG_SWIOTLB_SEGSIZE), users can adjust the segment size to
> > accommodate such use cases. This change improves flexibility and
> > ensures that systems can be tailored to meet the requirements of
> > specific hardware, such as the Hailo 8 PCIe AI card, without
> > requiring
> > kernel source modifications.
> >
> > I hope this example clarifies the need for this change. Please let
> > me
> > know if further details or additional examples are required.
> >
> > Best Regards,
> > Li Hua Qian
> > >
> > >
> > > > Li Hua Qian (1):
> > > >     swiotlb: Make IO_TLB_SEGSIZE configurable
> > > >
> > > >    include/linux/swiotlb.h | 2 +-
> > > >    kernel/dma/Kconfig      | 7 +++++++
> > > >    2 files changed, 8 insertions(+), 1 deletion(-)
> > > >
> > > Best regards
> >

--
Hua Qian Li
Siemens AG
http://www.siemens.com/