Re: [PATCH v4 5/7] iommu/dma: Make limit checks self-contained

Jerry Snitselaar
2024-05-18T18:31:13Z

On Fri, May 17, 2024 at 04:03:57PM GMT, Robin Murphy wrote:
> On 17/05/2024 3:21 pm, Jon Hunter wrote:
> >
> > On 15/05/2024 15:59, Robin Murphy wrote:
> > > Hi Jon,
> > >
> > > On 2024-05-14 2:27 pm, Jon Hunter wrote:
> > > > Hi Robin,
> > > >
> > > > On 19/04/2024 17:54, Robin Murphy wrote:
> > > > > It's now easy to retrieve the device's DMA limits if we want to check
> > > > > them against the domain aperture, so do that ourselves instead of
> > > > > relying on them being passed through the callchain.
> > > > >
> > > > > Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>
> > > > > Tested-by: Hanjun Guo <guohanjun@huawei.com>
> > > > > Signed-off-by: Robin Murphy <robin.murphy@arm.com>
> > > > > ---
> > > > >   drivers/iommu/dma-iommu.c | 21 +++++++++------------
> > > > >   1 file changed, 9 insertions(+), 12 deletions(-)
> > > > >
> > > > > diff --git a/drivers/iommu/dma-iommu.c b/drivers/iommu/dma-iommu.c
> > > > > index a3039005b696..f542eabaefa4 100644
> > > > > --- a/drivers/iommu/dma-iommu.c
> > > > > +++ b/drivers/iommu/dma-iommu.c
> > > > > @@ -660,19 +660,16 @@ static void
> > > > > iommu_dma_init_options(struct iommu_dma_options *options,
> > > > >   /**
> > > > >    * iommu_dma_init_domain - Initialise a DMA mapping domain
> > > > >    * @domain: IOMMU domain previously prepared by
> > > > > iommu_get_dma_cookie()
> > > > > - * @base: IOVA at which the mappable address space starts
> > > > > - * @limit: Last address of the IOVA space
> > > > >    * @dev: Device the domain is being initialised for
> > > > >    *
> > > > > - * @base and @limit + 1 should be exact multiples of IOMMU
> > > > > page granularity to
> > > > > - * avoid rounding surprises. If necessary, we reserve the
> > > > > page at address 0
> > > > > + * If the geometry and dma_range_map include address 0, we
> > > > > reserve that page
> > > > >    * to ensure it is an invalid IOVA. It is safe to
> > > > > reinitialise a domain, but
> > > > >    * any change which could make prior IOVAs invalid will fail.
> > > > >    */
> > > > > -static int iommu_dma_init_domain(struct iommu_domain
> > > > > *domain, dma_addr_t base,
> > > > > -                 dma_addr_t limit, struct device *dev)
> > > > > +static int iommu_dma_init_domain(struct iommu_domain
> > > > > *domain, struct device *dev)
> > > > >   {
> > > > >       struct iommu_dma_cookie *cookie = domain->iova_cookie;
> > > > > +    const struct bus_dma_region *map = dev->dma_range_map;
> > > > >       unsigned long order, base_pfn;
> > > > >       struct iova_domain *iovad;
> > > > >       int ret;
> > > > > @@ -684,18 +681,18 @@ static int
> > > > > iommu_dma_init_domain(struct iommu_domain *domain,
> > > > > dma_addr_t base,
> > > > >       /* Use the smallest supported page size for IOVA granularity */
> > > > >       order = __ffs(domain->pgsize_bitmap);
> > > > > -    base_pfn = max_t(unsigned long, 1, base >> order);
> > > > > +    base_pfn = 1;
> > > > >       /* Check the domain allows at least some access to the
> > > > > device... */
> > > > > -    if (domain->geometry.force_aperture) {
> > > > > +    if (map) {
> > > > > +        dma_addr_t base = dma_range_map_min(map);
> > > > >           if (base > domain->geometry.aperture_end ||
> > > > > -            limit < domain->geometry.aperture_start) {
> > > > > +            dma_range_map_max(map) <
> > > > > domain->geometry.aperture_start) {
> > > > >               pr_warn("specified DMA range outside IOMMU
> > > > > capability\n");
> > > > >               return -EFAULT;
> > > > >           }
> > > > >           /* ...then finally give it a kicking to make sure it fits */
> > > > > -        base_pfn = max_t(unsigned long, base_pfn,
> > > > > -                domain->geometry.aperture_start >> order);
> > > > > +        base_pfn = max(base,
> > > > > domain->geometry.aperture_start) >> order;
> > > > >       }
> > > > >       /* start_pfn is always nonzero for an
> > > > > already-initialised domain */
> > > > > @@ -1760,7 +1757,7 @@ void iommu_setup_dma_ops(struct device
> > > > > *dev, u64 dma_base, u64 dma_limit)
> > > > >        * underlying IOMMU driver needs to support via the
> > > > > dma-iommu layer.
> > > > >        */
> > > > >       if (iommu_is_dma_domain(domain)) {
> > > > > -        if (iommu_dma_init_domain(domain, dma_base, dma_limit, dev))
> > > > > +        if (iommu_dma_init_domain(domain, dev))
> > > > >               goto out_err;
> > > > >           dev->dma_ops = &iommu_dma_ops;
> > > > >       }
> > > >
> > > >
> > > > I have noticed some random test failures on Tegra186 and
> > > > Tegra194 and bisect is pointing to this commit. Reverting this
> > > > along with the various dependencies does fix the problem. On
> > > > Tegra186 CPU hotplug is failing and on Tegra194 suspend is
> > > > failing. Unfortunately, on neither platform do I see any
> > > > particular crash but the boards hang somewhere.
> > >
> > > That is... thoroughly bemusing :/ Not only is there supposed to be
> > > no real functional change here - we should merely be recalculating
> > > the same information from dev->dma_range_map that the callers were
> > > already doing to generate the base/limit arguments - but the act of
> > > initially setting up a default domain for a device behind an IOMMU
> > > should have no connection whatsoever to suspend and especially not
> > > to CPU hotplug.
> >
> >
> > Yes it does look odd, but this is what bisect reported ...
> >
> > git bisect start
> > # good: [a38297e3fb012ddfa7ce0321a7e5a8daeb1872b6] Linux 6.9
> > git bisect good a38297e3fb012ddfa7ce0321a7e5a8daeb1872b6
> > # bad: [6ba6c795dc73c22ce2c86006f17c4aa802db2a60] Add linux-next
> > specific files for 20240513
> > git bisect bad 6ba6c795dc73c22ce2c86006f17c4aa802db2a60
> > # good: [29e7f949865a023a21ecdfbd82d68ac697569f34] Merge branch 'main'
> > of git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net-next.git
> > git bisect good 29e7f949865a023a21ecdfbd82d68ac697569f34
> > # skip: [150e6cc14e51f2a07034106a4529cdaafd812c46] Merge branch 'next'
> > of git://git.kernel.org/pub/scm/linux/kernel/git/dtor/input.git
> > git bisect skip 150e6cc14e51f2a07034106a4529cdaafd812c46
> > # good: [f5d75327d30af49acf2e4b55f35ce2e6c45d1287] drm/amd/display: Fix
> > invalid Copyright notice
> > git bisect good f5d75327d30af49acf2e4b55f35ce2e6c45d1287
> > # skip: [f1ec9a9ffc526df7c9523006c2abbb8ea554cdd8] Merge branch
> > 'for-next' of
> > git://git.kernel.org/pub/scm/linux/kernel/git/krzk/linux-dt.git
> > git bisect skip f1ec9a9ffc526df7c9523006c2abbb8ea554cdd8
> > # bad: [f091e93306e0429ebb7589b9874590b6a9705e64] dma-mapping: Simplify
> > arch_setup_dma_ops()
> > git bisect bad f091e93306e0429ebb7589b9874590b6a9705e64
> > # good: [91cfd679f9e8b9a7bf2f26adf66eff99dbe2026b] ACPI/IORT: Handle
> > memory address size limits as limits
> > git bisect good 91cfd679f9e8b9a7bf2f26adf66eff99dbe2026b
> > # bad: [ad4750b07d3462ce29a0c9b1e88b2a1f9795290e] iommu/dma: Make limit
> > checks self-contained
> > git bisect bad ad4750b07d3462ce29a0c9b1e88b2a1f9795290e
> > # good: [fece6530bf4b59b01a476a12851e07751e73d69f] dma-mapping: Add
> > helpers for dma_range_map bounds
> > git bisect good fece6530bf4b59b01a476a12851e07751e73d69f
> > # first bad commit: [ad4750b07d3462ce29a0c9b1e88b2a1f9795290e]
> > iommu/dma: Make limit checks self-contained
> >
> > There is a couple skips in there and so I will try this again.
> >
> > > > If you have any ideas on things we can try let me know.
> > >
> > > Since the symptom seems inexplicable, I'd throw the usual memory
> > > debugging stuff like KASAN at it first. I'd also try
> > > "no_console_suspend" to check whether any late output is being
> > > missed in the suspend case (and if it's already broken, then any
> > > additional issues that may be caused by the console itself hopefully
> > > shouldn't matter).
> > >
> > > For more base-covering, do you have the "arm64: Properly clean up
> > > iommu-dma remnants" fix in there already as well? That bug has
> > > bisected to patch #6 each time though, so I do still suspect that
> > > what you're seeing is likely something else. It does seem
> > > potentially significant that those Tegra platforms are making fairly
> > > wide use of dma-ranges, but there's no clear idea forming out of
> > > that observation just yet...
> >
> > I was hoping it was the same issue other people had reported,
> > but the fix provided did not help. I have also tried today's
> > -next and I am still seeing the issue.
> >
> > I should have more time next week to look at this further. Let
> > me confirm which change is causing this and add more debug.
>
> Thanks. From staring at the code I think I've spotted one subtlety which
> may not be quite as intended - can you see if the diff below helps? It
> occurs to me that suspend and CPU hotplug may not *cause* the symptom,
> but they could certainly stall if one or more relevant CPUs is *already*
> stuck in a loop somewhere...
>
> Thanks,
> Robin.
>
> ----->8-----
> diff --git a/drivers/iommu/dma-iommu.c b/drivers/iommu/dma-iommu.c
> index 89a53c2f2cf9..85eb1846c637 100644
> --- a/drivers/iommu/dma-iommu.c
> +++ b/drivers/iommu/dma-iommu.c
> @@ -686,6 +686,7 @@ static int iommu_dma_init_domain(struct iommu_domain *domain, struct device *dev
> /* Check the domain allows at least some access to the device... */
> if (map) {
> dma_addr_t base = dma_range_map_min(map);
> + base = max(base, (dma_addr_t)1 << order);
> if (base > domain->geometry.aperture_end ||
> dma_range_map_max(map) < domain->geometry.aperture_start) {
> pr_warn("specified DMA range outside IOMMU capability\n");

With this in place I no longer see the mapping fail on the nvidia system.

Regards,
Jerry