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

Jon Hunter
2024-05-17T14:22:13Z

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.

Jon

--
nvpublic