On Wed, May 14, 2025 at 10:53:19AM -0700, Rob Clark wrote:
> From: Rob Clark <robdcl...@chromium.org>
>
> In situations where mapping/unmapping sequence can be controlled by
> userspace, attempting to map over a region that has not yet been
> unmapped is an error. But not something that should spam dmesg.
>
> Now that there is a quirk, we can also drop the selftest_running
> flag, and use the quirk instead for selftests.
>
> Signed-off-by: Rob Clark <robdcl...@chromium.org>
> Acked-by: Robin Murphy <robin.mur...@arm.com>
> Signed-off-by: Rob Clark <robdcl...@chromium.org>
> ---
> drivers/iommu/io-pgtable-arm.c | 27 ++++++++++++++-------------
> include/linux/io-pgtable.h | 8 ++++++++
> 2 files changed, 22 insertions(+), 13 deletions(-)
[...]
> diff --git a/include/linux/io-pgtable.h b/include/linux/io-pgtable.h
> index bba2a51c87d2..639b8f4fb87d 100644
> --- a/include/linux/io-pgtable.h
> +++ b/include/linux/io-pgtable.h
> @@ -88,6 +88,13 @@ struct io_pgtable_cfg {
> *
> * IO_PGTABLE_QUIRK_ARM_HD: Enables dirty tracking in stage 1 pagetable.
> * IO_PGTABLE_QUIRK_ARM_S2FWB: Use the FWB format for the MemAttrs bits
> + *
> + * IO_PGTABLE_QUIRK_NO_WARN_ON: Do not WARN_ON() on conflicting
> + * mappings, but silently return -EEXISTS. Normally an attempt
> + * to map over an existing mapping would indicate some sort of
> + * kernel bug, which would justify the WARN_ON(). But for GPU
> + * drivers, this could be under control of userspace. Which
> + * deserves an error return, but not to spam dmesg.
> */
> #define IO_PGTABLE_QUIRK_ARM_NS BIT(0)
> #define IO_PGTABLE_QUIRK_NO_PERMS BIT(1)
> @@ -97,6 +104,7 @@ struct io_pgtable_cfg {
> #define IO_PGTABLE_QUIRK_ARM_OUTER_WBWA BIT(6)
> #define IO_PGTABLE_QUIRK_ARM_HD BIT(7)
> #define IO_PGTABLE_QUIRK_ARM_S2FWB BIT(8)
> + #define IO_PGTABLE_QUIRK_NO_WARN_ON BIT(9)
This feels a bit fragile to me:
* IOMMU-API users of io-pgtable shouldn't be passing this quirk
but might end up doing so to paper over driver bugs.
* Low-level users of io-pgtable who expose page-table operations to
userspace need to pass the quirk, but might well not bother because
well-behaved userspace doesn't trigger the warning.
So overall, it's all a bit unsatisfactory. Is there a way we could have
the warnings only when invoked via the IOMMU API?
Will
