Hi Baolu,
On 2021/4/14 15:14, Lu Baolu wrote:
> On 4/13/21 4:54 PM, Keqian Zhu wrote:
>> Block(largepage) mapping is not a proper granule for dirty log tracking.
>> Take an extreme example, if DMA writes one byte, under 1G mapping, the
>> dirty amount reported is 1G, but under 4K mapping, the dirty amount is
>> just 4K.
>>
>> This adds a new interface named iommu_split_block in IOMMU base layer.
>> A specific IOMMU driver can invoke it during start dirty log. If so, the
>> driver also need to realize the split_block iommu ops.
>>
>> We flush all iotlbs after the whole procedure is completed to ease the
>> pressure of IOMMU, as we will hanle a huge range of mapping in general.
>>
>> Signed-off-by: Keqian Zhu <zhukeqi...@huawei.com>
>> Signed-off-by: Kunkun Jiang <jiangkun...@huawei.com>
>> ---
>> drivers/iommu/iommu.c | 41 +++++++++++++++++++++++++++++++++++++++++
>> include/linux/iommu.h | 11 +++++++++++
>> 2 files changed, 52 insertions(+)
>>
>> diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
>> index 667b2d6d2fc0..bb413a927870 100644
>> --- a/drivers/iommu/iommu.c
>> +++ b/drivers/iommu/iommu.c
>> @@ -2721,6 +2721,47 @@ int iommu_domain_set_attr(struct iommu_domain *domain,
>> }
>> EXPORT_SYMBOL_GPL(iommu_domain_set_attr);
>> +int iommu_split_block(struct iommu_domain *domain, unsigned long iova,
>> + size_t size)
>> +{
>> + const struct iommu_ops *ops = domain->ops;
>> + unsigned int min_pagesz;
>> + size_t pgsize;
>> + bool flush = false;
>> + int ret = 0;
>> +
>> + if (unlikely(!ops || !ops->split_block))
>> + return -ENODEV;
>> +
>> + min_pagesz = 1 << __ffs(domain->pgsize_bitmap);
>> + if (!IS_ALIGNED(iova | size, min_pagesz)) {
>> + pr_err("unaligned: iova 0x%lx size 0x%zx min_pagesz 0x%x\n",
>> + iova, size, min_pagesz);
>> + return -EINVAL;
>> + }
>> +
>> + while (size) {
>> + flush = true;
>> +
>> + pgsize = iommu_pgsize(domain, iova, size);
>> +
>> + ret = ops->split_block(domain, iova, pgsize);
>> + if (ret)
>> + break;
>> +
>> + pr_debug("split handled: iova 0x%lx size 0x%zx\n", iova, pgsize);
>> +
>> + iova += pgsize;
>> + size -= pgsize;
>> + }
>> +
>> + if (flush)
>> + iommu_flush_iotlb_all(domain);
>> +
>> + return ret;
>> +}
>> +EXPORT_SYMBOL_GPL(iommu_split_block);
>
> Do you really have any consumers of this interface other than the dirty
> bit tracking? If not, I don't suggest to make this as a generic IOMMU
> interface.
>
> There is an implicit requirement for such interfaces. The
> iommu_map/unmap(iova, size) shouldn't be called at the same time.
> Currently there's no such sanity check in the iommu core. A poorly
> written driver could mess up the kernel by misusing this interface.
Yes, I don't think up a scenario except dirty tracking.
Indeed, we'd better not make them as a generic interface.
Do you have any suggestion that underlying iommu drivers can share these code
but
not make it as a generic iommu interface?
I have a not so good idea. Make the "split" interfaces as a static function, and
transfer the function pointer to start_dirty_log. But it looks weird and
inflexible.
On the other hand, if a driver calls map/unmap with split/merge at the same
time,
it's a bug of driver, it should follow the rule.
>
> This also applies to iommu_merge_page().
>
Thanks,
Keqian
