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Message-ID: <CAF6AEGs8gPtmYeYBMCn3r=w4eq4pk25fdS=YeqMYUySj7kz0ow@mail.gmail.com>
Date: Tue, 29 Apr 2025 06:59:20 -0700
From: Rob Clark <robdclark@...il.com>
To: Robin Murphy <robin.murphy@....com>
Cc: dri-devel@...ts.freedesktop.org, freedreno@...ts.freedesktop.org,
linux-arm-msm@...r.kernel.org, Connor Abbott <cwabbott0@...il.com>,
Rob Clark <robdclark@...omium.org>, Will Deacon <will@...nel.org>, Joerg Roedel <joro@...tes.org>,
Jason Gunthorpe <jgg@...pe.ca>, Nicolin Chen <nicolinc@...dia.com>, Kevin Tian <kevin.tian@...el.com>,
Joao Martins <joao.m.martins@...cle.com>,
"moderated list:ARM SMMU DRIVERS" <linux-arm-kernel@...ts.infradead.org>,
"open list:IOMMU SUBSYSTEM" <iommu@...ts.linux.dev>, open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3 03/33] iommu/io-pgtable-arm: Add quirk to quiet WARN_ON()
On Tue, Apr 29, 2025 at 5:38 AM Robin Murphy <robin.murphy@....com> wrote:
>
> On 28/04/2025 9:54 pm, Rob Clark wrote:
> > From: Rob Clark <robdclark@...omium.org>
> >
> > In situations where mapping/unmapping squence 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.
> >
> > Signed-off-by: Rob Clark <robdclark@...omium.org>
> > ---
> > drivers/iommu/io-pgtable-arm.c | 18 ++++++++++++------
> > include/linux/io-pgtable.h | 8 ++++++++
> > 2 files changed, 20 insertions(+), 6 deletions(-)
> >
> > diff --git a/drivers/iommu/io-pgtable-arm.c b/drivers/iommu/io-pgtable-arm.c
> > index f27965caf6a1..99523505dac5 100644
> > --- a/drivers/iommu/io-pgtable-arm.c
> > +++ b/drivers/iommu/io-pgtable-arm.c
> > @@ -475,7 +475,7 @@ static int __arm_lpae_map(struct arm_lpae_io_pgtable *data, unsigned long iova,
> > cptep = iopte_deref(pte, data);
> > } else if (pte) {
> > /* We require an unmap first */
> > - WARN_ON(!selftest_running);
> > + WARN_ON(!selftest_running && !(cfg->quirks & IO_PGTABLE_QUIRK_NO_WARN_ON));
>
> If we are going to have this as a general mechanism then the selftests
> should use it as well.
Makes sense, I can remove the selftest_running hack in the next version.
BR,
-R
> Thanks,
> Robin.
>
> > return -EEXIST;
> > }
> >
> > @@ -649,8 +649,10 @@ static size_t __arm_lpae_unmap(struct arm_lpae_io_pgtable *data,
> > unmap_idx_start = ARM_LPAE_LVL_IDX(iova, lvl, data);
> > ptep += unmap_idx_start;
> > pte = READ_ONCE(*ptep);
> > - if (WARN_ON(!pte))
> > - return 0;
> > + if (!pte) {
> > + WARN_ON(!(data->iop.cfg.quirks & IO_PGTABLE_QUIRK_NO_WARN_ON));
> > + return -ENOENT;
> > + }
> >
> > /* If the size matches this level, we're in the right place */
> > if (size == ARM_LPAE_BLOCK_SIZE(lvl, data)) {
> > @@ -660,8 +662,10 @@ static size_t __arm_lpae_unmap(struct arm_lpae_io_pgtable *data,
> > /* Find and handle non-leaf entries */
> > for (i = 0; i < num_entries; i++) {
> > pte = READ_ONCE(ptep[i]);
> > - if (WARN_ON(!pte))
> > + if (!pte) {
> > + WARN_ON(!(data->iop.cfg.quirks & IO_PGTABLE_QUIRK_NO_WARN_ON));
> > break;
> > + }
> >
> > if (!iopte_leaf(pte, lvl, iop->fmt)) {
> > __arm_lpae_clear_pte(&ptep[i], &iop->cfg, 1);
> > @@ -976,7 +980,8 @@ arm_64_lpae_alloc_pgtable_s1(struct io_pgtable_cfg *cfg, void *cookie)
> > if (cfg->quirks & ~(IO_PGTABLE_QUIRK_ARM_NS |
> > IO_PGTABLE_QUIRK_ARM_TTBR1 |
> > IO_PGTABLE_QUIRK_ARM_OUTER_WBWA |
> > - IO_PGTABLE_QUIRK_ARM_HD))
> > + IO_PGTABLE_QUIRK_ARM_HD |
> > + IO_PGTABLE_QUIRK_NO_WARN_ON))
> > return NULL;
> >
> > data = arm_lpae_alloc_pgtable(cfg);
> > @@ -1079,7 +1084,8 @@ arm_64_lpae_alloc_pgtable_s2(struct io_pgtable_cfg *cfg, void *cookie)
> > struct arm_lpae_io_pgtable *data;
> > typeof(&cfg->arm_lpae_s2_cfg.vtcr) vtcr = &cfg->arm_lpae_s2_cfg.vtcr;
> >
> > - if (cfg->quirks & ~(IO_PGTABLE_QUIRK_ARM_S2FWB))
> > + if (cfg->quirks & ~(IO_PGTABLE_QUIRK_ARM_S2FWB |
> > + IO_PGTABLE_QUIRK_NO_WARN_ON))
> > return NULL;
> >
> > data = arm_lpae_alloc_pgtable(cfg);
> > 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)
> > unsigned long quirks;
> > unsigned long pgsize_bitmap;
> > unsigned int ias;
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