Hi, On Tue, Jun 22, 2021 at 10:46 AM John Garry <john.garry@xxxxxxxxxx> wrote: > > On 22/06/2021 00:52, Douglas Anderson wrote: > > > > This patch attempts to put forward a proposal for enabling non-strict > > DMA on a device-by-device basis. The patch series requests non-strict > > DMA for the Qualcomm SDHCI controller as a first device to enable, > > getting a nice bump in performance with what's believed to be a very > > small drop in security / safety (see the patch for the full argument). > > > > As part of this patch series I am end up slightly cleaning up some of > > the interactions between the PCI subsystem and the IOMMU subsystem but > > I don't go all the way to fully remove all the tentacles. Specifically > > this patch series only concerns itself with a single aspect: strict > > vs. non-strict mode for the IOMMU. I'm hoping that this will be easier > > to talk about / reason about for more subsystems compared to overall > > deciding what it means for a device to be "external" or "untrusted". > > > > If something like this patch series ends up being landable, it will > > undoubtedly need coordination between many maintainers to land. I > > believe it's fully bisectable but later patches in the series > > definitely depend on earlier ones. Sorry for the long CC list. :( > > > > JFYI, In case to missed it, and I know it's not the same thing as you > want, above, but the following series will allow you to build the kernel > to default to lazy mode: > > https://lore.kernel.org/linux-iommu/1624016058-189713-1-git-send-email-john.garry@xxxxxxxxxx/T/#m21bc07b9353b3ba85f2a40557645c2bcc13cbb3e > > So iommu.strict=0 would be no longer always required for arm64. Excellent! I'm never a fan of command line parameters as a replacement for Kconfig. They are great for debugging or for cases where the user of the kernel and the person compiling the kernel are not the same (like with off-the-shelf Linux distros) but aren't great for setting a default for embedded environments. I actually think that something like my patchset may be even more important atop yours. Do you agree? If the default is non-strict it could be extra important to be able to mark a certain device to be in "strict" mode. ...also, unfortunately I probably won't be able to use your patchest for my use case. I think we want the extra level of paranoia by default and really only want to allow non-strict mode for devices that we're really convinced are safe. -Doug
