On 2025-05-20 12:31 pm, Will Deacon wrote:
On Thu, May 15, 2025 at 07:48:39AM -0700, Rob Clark wrote:
On Thu, May 15, 2025 at 7:33 AM Will Deacon <w...@kernel.org> wrote:
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?
iommu drivers _not_ setting this flag seems like a good way to achieve that ;-)
The alternative is to move the warns to the iommu driver... but they
could just as easily remove the WARN_ON()s as they could set the
NO_WARN_ON quirk, so :shrug:?
Bah, I also don't have a good idea to improve this, so I guess I'll take
what you have for now.
Hmm, just a nit on reflection, how about fixing up the name to just
IO_PGTABLE_QUIRK_NO_WARN? Given that it's already quite long, and we
have a well-established DMA_ATTR_NO_WARN with equivalent semantics over
in the DMA API.
Cheers,
Robin.
