On Tue, 12 Jan 2021 20:04:38 +0800
Keqian Zhu <zhukeqian1@xxxxxxxxxx> wrote:
> On 2021/1/12 5:49, Alex Williamson wrote:
> > On Thu, 7 Jan 2021 17:29:00 +0800
> > Keqian Zhu <zhukeqian1@xxxxxxxxxx> wrote:
> >
> >> If we detach group during dirty page tracking, we shouldn't remove
> >> vfio_dma, because dirty log will lose.
> >>
> >> But we don't prevent unmap_unpin_all in vfio_iommu_release, because
> >> under normal procedure, dirty tracking has been stopped.
> >
> > This looks like it's creating a larger problem than it's fixing, it's
> > not our job to maintain the dirty bitmap regardless of what the user
> > does. If the user detaches the last group in a container causing the
> > mappings within that container to be deconstructed before the user has
> > collected dirty pages, that sounds like a user error. A container with
> > no groups is de-privileged and therefore loses all state. Thanks,
> >
> > Alex
>
> Hi Alex,
>
> This looks good to me ;-). That's a reasonable constraint for user behavior.
>
> What about replacing this patch with an addition to the uapi document of
> VFIO_GROUP_UNSET_CONTAINER? User should pay attention to this when call this
> ioctl during dirty tracking.
Here's the current uapi comment:
/**
* VFIO_GROUP_UNSET_CONTAINER - _IO(VFIO_TYPE, VFIO_BASE + 5)
*
* Remove the group from the attached container. This is the
* opposite of the SET_CONTAINER call and returns the group to
* an initial state. All device file descriptors must be released
* prior to calling this interface. When removing the last group
* from a container, the IOMMU will be disabled and all state lost,
* effectively also returning the VFIO file descriptor to an initial
* state.
* Return: 0 on success, -errno on failure.
* Availability: When attached to container
*/
So we already indicate that "all state" of the container is lost when
removing the last group, I don't see that it's necessarily to
explicitly include dirty bitmap state beyond that statement. Without
mappings there can be no dirty bitmap to track.
> And any comments on other patches? thanks.
I had a difficult time mapping the commit log to the actual code
change, I'll likely have some wording suggestions. Is patch 5/5 still
necessary if this patch is dropped? Thanks,
Alex
> >> Fixes: d6a4c185660c ("vfio iommu: Implementation of ioctl for dirty pages tracking")
> >> Signed-off-by: Keqian Zhu <zhukeqian1@xxxxxxxxxx>
> >> ---
> >> drivers/vfio/vfio_iommu_type1.c | 14 ++++++++++++--
> >> 1 file changed, 12 insertions(+), 2 deletions(-)
> >>
> >> diff --git a/drivers/vfio/vfio_iommu_type1.c b/drivers/vfio/vfio_iommu_type1.c
> >> index 26b7eb2a5cfc..9776a059904d 100644
> >> --- a/drivers/vfio/vfio_iommu_type1.c
> >> +++ b/drivers/vfio/vfio_iommu_type1.c
> >> @@ -2373,7 +2373,12 @@ static void vfio_iommu_type1_detach_group(void *iommu_data,
> >> if (list_empty(&iommu->external_domain->group_list)) {
> >> vfio_sanity_check_pfn_list(iommu);
> >>
> >> - if (!IS_IOMMU_CAP_DOMAIN_IN_CONTAINER(iommu))
> >> + /*
> >> + * During dirty page tracking, we can't remove
> >> + * vfio_dma because dirty log will lose.
> >> + */
> >> + if (!IS_IOMMU_CAP_DOMAIN_IN_CONTAINER(iommu) &&
> >> + !iommu->dirty_page_tracking)
> >> vfio_iommu_unmap_unpin_all(iommu);
> >>
> >> kfree(iommu->external_domain);
> >> @@ -2406,10 +2411,15 @@ static void vfio_iommu_type1_detach_group(void *iommu_data,
> >> * iommu and external domain doesn't exist, then all the
> >> * mappings go away too. If it's the last domain with iommu and
> >> * external domain exist, update accounting
> >> + *
> >> + * Note: During dirty page tracking, we can't remove vfio_dma
> >> + * because dirty log will lose. Just update accounting is a good
> >> + * choice.
> >> */
> >> if (list_empty(&domain->group_list)) {
> >> if (list_is_singular(&iommu->domain_list)) {
> >> - if (!iommu->external_domain)
> >> + if (!iommu->external_domain &&
> >> + !iommu->dirty_page_tracking)
> >> vfio_iommu_unmap_unpin_all(iommu);
> >> else
> >> vfio_iommu_unmap_unpin_reaccount(iommu);
> >
> > .
> >
>
