Re: [PATCH v3 01/12] iommu: Introduce dirty log tracking framework

[Lu Baolu]

On 4/15/21 2:18 PM, Keqian Zhu wrote:
> Hi Baolu,
>
> Thanks for the review!
>
> On 2021/4/14 15:00, Lu Baolu wrote:
> > Hi Keqian,
> >
> > On 4/13/21 4:54 PM, Keqian Zhu wrote:
> > > Some types of IOMMU are capable of tracking DMA dirty log, such as
> > > ARM SMMU with HTTU or Intel IOMMU with SLADE. This introduces the
> > > dirty log tracking framework in the IOMMU base layer.
> > >
> > > Three new essential interfaces are added, and we maintaince the status
> > > of dirty log tracking in iommu_domain.
> > > 1. iommu_switch_dirty_log: Perform actions to start|stop dirty log tracking
> > > 2. iommu_sync_dirty_log: Sync dirty log from IOMMU into a dirty bitmap
> > > 3. iommu_clear_dirty_log: Clear dirty log of IOMMU by a mask bitmap
> > >
> > > A new dev feature are added to indicate whether a specific type of
> > > iommu hardware supports and its driver realizes them.
> > >
> > > Signed-off-by: Keqian Zhu <zhukeqian1@xxxxxxxxxx>
> > > Signed-off-by: Kunkun Jiang <jiangkunkun@xxxxxxxxxx>
> > > ---
> > >    drivers/iommu/iommu.c | 150 ++++++++++++++++++++++++++++++++++++++++++
> > >    include/linux/iommu.h |  53 +++++++++++++++
> > >    2 files changed, 203 insertions(+)
> > >
> > > diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
> > > index d0b0a15dba84..667b2d6d2fc0 100644
> > > --- a/drivers/iommu/iommu.c
> > > +++ b/drivers/iommu/iommu.c
> > > @@ -1922,6 +1922,7 @@ static struct iommu_domain *__iommu_domain_alloc(struct bus_type *bus,
> > >        domain->type = type;
> > >        /* Assume all sizes by default; the driver may override this later */
> > >        domain->pgsize_bitmap  = bus->iommu_ops->pgsize_bitmap;
> > > +    mutex_init(&domain->switch_log_lock);
> > >          return domain;
> > >    }
> > > @@ -2720,6 +2721,155 @@ int iommu_domain_set_attr(struct iommu_domain *domain,
> > >    }
> > >    EXPORT_SYMBOL_GPL(iommu_domain_set_attr);
> > >    +int iommu_switch_dirty_log(struct iommu_domain *domain, bool enable,
> > > +               unsigned long iova, size_t size, int prot)
> > > +{
> > > +    const struct iommu_ops *ops = domain->ops;
> > > +    int ret;
> > > +
> > > +    if (unlikely(!ops || !ops->switch_dirty_log))
> > > +        return -ENODEV;
> > > +
> > > +    mutex_lock(&domain->switch_log_lock);
> > > +    if (enable && domain->dirty_log_tracking) {
> > > +        ret = -EBUSY;
> > > +        goto out;
> > > +    } else if (!enable && !domain->dirty_log_tracking) {
> > > +        ret = -EINVAL;
> > > +        goto out;
> > > +    }
> > > +
> > > +    ret = ops->switch_dirty_log(domain, enable, iova, size, prot);
> > > +    if (ret)
> > > +        goto out;
> > > +
> > > +    domain->dirty_log_tracking = enable;
> > > +out:
> > > +    mutex_unlock(&domain->switch_log_lock);
> > > +    return ret;
> > > +}
> > > +EXPORT_SYMBOL_GPL(iommu_switch_dirty_log);
> >
> > Since you also added IOMMU_DEV_FEAT_HWDBM, I am wondering what's the
> > difference between
> >
> > iommu_switch_dirty_log(on) vs. iommu_dev_enable_feature(IOMMU_DEV_FEAT_HWDBM)
> >
> > iommu_switch_dirty_log(off) vs. iommu_dev_disable_feature(IOMMU_DEV_FEAT_HWDBM)
> Indeed. As I can see, IOMMU_DEV_FEAT_AUX is not switchable, so enable/disable
> are not applicable for it. IOMMU_DEV_FEAT_SVA is switchable, so we can use these
> interfaces for it.
>
> IOMMU_DEV_FEAT_HWDBM is used to indicate whether hardware supports HWDBM, so we should

Previously we had iommu_dev_has_feature() and then was cleaned up due to
lack of real users. If you have a real case for it, why not bringing it
back?

> design it as not switchable. I will modify the commit message of patch#12, thanks!

I am not sure that I fully get your point. But I can't see any gaps of
using iommu_dev_enable/disable_feature() to switch dirty log on and off.
Probably I missed anything.

> > > +
> > > +int iommu_sync_dirty_log(struct iommu_domain *domain, unsigned long iova,
> > > +             size_t size, unsigned long *bitmap,
> > > +             unsigned long base_iova, unsigned long bitmap_pgshift)
> > > +{
> > > +    const struct iommu_ops *ops = domain->ops;
> > > +    unsigned int min_pagesz;
> > > +    size_t pgsize;
> > > +    int ret = 0;
> > > +
> > > +    if (unlikely(!ops || !ops->sync_dirty_log))
> > > +        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;
> > > +    }
> > > +
> > > +    mutex_lock(&domain->switch_log_lock);
> > > +    if (!domain->dirty_log_tracking) {
> > > +        ret = -EINVAL;
> > > +        goto out;
> > > +    }
> > > +
> > > +    while (size) {
> > > +        pgsize = iommu_pgsize(domain, iova, size);
> > > +
> > > +        ret = ops->sync_dirty_log(domain, iova, pgsize,
> > > +                      bitmap, base_iova, bitmap_pgshift);
> >
> > Any reason why do you want to do this in a per-4K page manner? This can
> > lead to a lot of indirect calls and bad performance.
> >
> > How about a sync_dirty_pages()?
> The function name of iommu_pgsize() is a bit puzzling. Actually it will try to
> compute the max size that fit into size, so the pgsize can be a large page size
> even if the underlying mapping is 4K. The __iommu_unmap() also has a similar logic.

This series has some improvement on the iommu_pgsize() helper.

https://lore.kernel.org/linux-iommu/20210405191112.28192-1-isaacm@xxxxxxxxxxxxxx/

Best regards,
baolu