linux-kernel - Re: [PATCH 0/6] iommu: Enable devices to request non-strict DMA, starting with QCom SD/MMC

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Date:   Tue, 22 Jun 2021 18:39:50 +0100
From:   John Garry <john.garry@...wei.com>
To:     Douglas Anderson <dianders@...omium.org>,
        <gregkh@...uxfoundation.org>, <rafael@...nel.org>,
        <rafael.j.wysocki@...el.com>, <will@...nel.org>,
        <robin.murphy@....com>, <joro@...tes.org>,
        <bjorn.andersson@...aro.org>, <ulf.hansson@...aro.org>,
        <adrian.hunter@...el.com>, <bhelgaas@...gle.com>
CC:     <robdclark@...omium.org>, <linux-arm-msm@...r.kernel.org>,
        <linux-pci@...r.kernel.org>, <quic_c_gdjako@...cinc.com>,
        <iommu@...ts.linux-foundation.org>, <sonnyrao@...omium.org>,
        <saiprakash.ranjan@...eaurora.org>, <linux-mmc@...r.kernel.org>,
        <vbadigan@...eaurora.org>, <rajatja@...gle.com>,
        <saravanak@...gle.com>, <joel@...lfernandes.org>,
        Andy Gross <agross@...nel.org>,
        Bartosz Golaszewski <bgolaszewski@...libre.com>,
        Dan Williams <dan.j.williams@...el.com>,
        "Geert Uytterhoeven" <geert@...ux-m68k.org>,
        Heikki Krogerus <heikki.krogerus@...ux.intel.com>,
        Randy Dunlap <rdunlap@...radead.org>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 0/6] iommu: Enable devices to request non-strict DMA,
 starting with QCom SD/MMC

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@huawei.com/T/#m21bc07b9353b3ba85f2a40557645c2bcc13cbb3e

So iommu.strict=0 would be no longer always required for arm64.

Thanks,
John


> 
> Douglas Anderson (6):
>    drivers: base: Add the concept of "pre_probe" to drivers
>    drivers: base: Add bits to struct device to control iommu strictness
>    PCI: Indicate that we want to force strict DMA for untrusted devices
>    iommu: Combine device strictness requests with the global default
>    iommu: Stop reaching into PCIe devices to decide strict vs. non-strict
>    mmc: sdhci-msm: Request non-strict IOMMU mode
> 
>   drivers/base/dd.c             | 10 +++++--
>   drivers/iommu/dma-iommu.c     |  2 +-
>   drivers/iommu/iommu.c         | 56 +++++++++++++++++++++++++++--------
>   drivers/mmc/host/sdhci-msm.c  |  8 +++++
>   drivers/pci/probe.c           |  4 ++-
>   include/linux/device.h        | 11 +++++++
>   include/linux/device/driver.h |  9 ++++++
>   include/linux/iommu.h         |  2 ++
>   8 files changed, 85 insertions(+), 17 deletions(-)
>