Re: [RFC PATCH 10/11] vfio/iommu_type1: Optimize dirty bitmap population based on iommu HWDBM
On 21-02-09 11:16:08, Robin Murphy wrote:
> On 2021-02-07 09:56, Yi Sun wrote:
> >Hi,
> >
> >On 21-01-28 23:17:41, Keqian Zhu wrote:
> >
> >[...]
> >
> >>+static void vfio_dma_dirty_log_start(struct vfio_iommu *iommu,
> >>+struct vfio_dma *dma)
> >>+{
> >>+ struct vfio_domain *d;
> >>+
> >>+ list_for_each_entry(d, >domain_list, next) {
> >>+ /* Go through all domain anyway even if we fail */
> >>+ iommu_split_block(d->domain, dma->iova, dma->size);
> >>+ }
> >>+}
> >
> >This should be a switch to prepare for dirty log start. Per Intel
> >Vtd spec, there is SLADE defined in Scalable-Mode PASID Table Entry.
> >It enables Accessed/Dirty Flags in second-level paging entries.
> >So, a generic iommu interface here is better. For Intel iommu, it
> >enables SLADE. For ARM, it splits block.
>
> From a quick look, VT-D's SLADE and SMMU's HTTU appear to be the
> exact same thing. This step isn't about enabling or disabling that
> feature itself (the proposal for SMMU is to simply leave HTTU
> enabled all the time), it's about controlling the granularity at
> which the dirty status can be detected/reported at all, since that's
> tied to the pagetable structure.
>
> However, if an IOMMU were to come along with some other way of
> reporting dirty status that didn't depend on the granularity of
> individual mappings, then indeed it wouldn't need this operation.
>
Per my thought, we can use these two start/stop interfaces to make
user space decide when to start/stop the dirty tracking. For Intel
SLADE, I think we can enable this bit when this start interface is
called by user space. I don't think leave SLADE enabled all the time
is necessary for Intel Vt-d. So I suggest a generic interface here.
Thanks!
> Robin.
>
> >>+
> >>+static void vfio_dma_dirty_log_stop(struct vfio_iommu *iommu,
> >>+ struct vfio_dma *dma)
> >>+{
> >>+ struct vfio_domain *d;
> >>+
> >>+ list_for_each_entry(d, >domain_list, next) {
> >>+ /* Go through all domain anyway even if we fail */
> >>+ iommu_merge_page(d->domain, dma->iova, dma->size,
> >>+d->prot | dma->prot);
> >>+ }
> >>+}
> >
> >Same as above comment, a generic interface is required here.
> >
> >>+
> >>+static void vfio_iommu_dirty_log_switch(struct vfio_iommu *iommu, bool
> >>start)
> >>+{
> >>+ struct rb_node *n;
> >>+
> >>+ /* Split and merge even if all iommu don't support HWDBM now */
> >>+ for (n = rb_first(>dma_list); n; n = rb_next(n)) {
> >>+ struct vfio_dma *dma = rb_entry(n, struct vfio_dma, node);
> >>+
> >>+ if (!dma->iommu_mapped)
> >>+ continue;
> >>+
> >>+ /* Go through all dma range anyway even if we fail */
> >>+ if (start)
> >>+ vfio_dma_dirty_log_start(iommu, dma);
> >>+ else
> >>+ vfio_dma_dirty_log_stop(iommu, dma);
> >>+ }
> >>+}
> >>+
> >> static int vfio_iommu_type1_dirty_pages(struct vfio_iommu *iommu,
> >>unsigned long arg)
> >> {
> >>@@ -2812,8 +2900,10 @@ static int vfio_iommu_type1_dirty_pages(struct
> >>vfio_iommu *iommu,
> >>pgsize = 1 << __ffs(iommu->pgsize_bitmap);
> >>if (!iommu->dirty_page_tracking) {
> >>ret = vfio_dma_bitmap_alloc_all(iommu, pgsize);
> >>- if (!ret)
> >>+ if (!ret) {
> >>iommu->dirty_page_tracking = true;
> >>+ vfio_iommu_dirty_log_switch(iommu, true);
> >>+ }
> >>}
> >>mutex_unlock(>lock);
> >>return ret;
> >>@@ -2822,6 +2912,7 @@ static int vfio_iommu_type1_dirty_pages(struct
> >>vfio_iommu *iommu,
> >>if (iommu->dirty_page_tracking) {
> >>iommu->dirty_page_tracking = false;
> >>vfio_dma_bitmap_free_all(iommu);
> >>+ vfio_iommu_dirty_log_switch(iommu, false);
> >>}
> >>mutex_unlock(>lock);
> >>return 0;
> >>--
> >>2.19.1
> >___
> >iommu mailing list
> >io...@lists.linux-foundation.org
> >https://lists.linuxfoundation.org/mailman/listinfo/iommu
> >
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Re: [RFC PATCH 10/11] vfio/iommu_type1: Optimize dirty bitmap population based on iommu HWDBM
On 21-02-07 18:40:36, Keqian Zhu wrote:
> Hi Yi,
>
> On 2021/2/7 17:56, Yi Sun wrote:
> > Hi,
> >
> > On 21-01-28 23:17:41, Keqian Zhu wrote:
> >
> > [...]
> >
> >> +static void vfio_dma_dirty_log_start(struct vfio_iommu *iommu,
> >> + struct vfio_dma *dma)
> >> +{
> >> + struct vfio_domain *d;
> >> +
> >> + list_for_each_entry(d, >domain_list, next) {
> >> + /* Go through all domain anyway even if we fail */
> >> + iommu_split_block(d->domain, dma->iova, dma->size);
> >> + }
> >> +}
> >
> > This should be a switch to prepare for dirty log start. Per Intel
> > Vtd spec, there is SLADE defined in Scalable-Mode PASID Table Entry.
> > It enables Accessed/Dirty Flags in second-level paging entries.
> > So, a generic iommu interface here is better. For Intel iommu, it
> > enables SLADE. For ARM, it splits block.
> Indeed, a generic interface name is better.
>
> The vendor iommu driver plays vendor's specific actions to start dirty log,
> and Intel iommu and ARM smmu may differ. Besides, we may add more actions in
> ARM smmu driver in future.
>
> One question: Though I am not familiar with Intel iommu, I think it also
> should split block mapping besides enable SLADE. Right?
>
I am not familiar with ARM smmu. :) So I want to clarify if the block
in smmu is big page, e.g. 2M page? Intel Vtd manages the memory per
page, 4KB/2MB/1GB. There are two ways to manage dirty pages.
1. Keep default granularity. Just set SLADE to enable the dirty track.
2. Split big page to 4KB to get finer granularity.
But question about the second solution is if it can benefit the user
space, e.g. live migration. If my understanding about smmu block (i.e.
the big page) is correct, have you collected some performance data to
prove that the split can improve performance? Thanks!
> Thanks,
> Keqian
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Re: [RFC PATCH 10/11] vfio/iommu_type1: Optimize dirty bitmap population based on iommu HWDBM
Hi,
On 21-01-28 23:17:41, Keqian Zhu wrote:
[...]
> +static void vfio_dma_dirty_log_start(struct vfio_iommu *iommu,
> + struct vfio_dma *dma)
> +{
> + struct vfio_domain *d;
> +
> + list_for_each_entry(d, >domain_list, next) {
> + /* Go through all domain anyway even if we fail */
> + iommu_split_block(d->domain, dma->iova, dma->size);
> + }
> +}
This should be a switch to prepare for dirty log start. Per Intel
Vtd spec, there is SLADE defined in Scalable-Mode PASID Table Entry.
It enables Accessed/Dirty Flags in second-level paging entries.
So, a generic iommu interface here is better. For Intel iommu, it
enables SLADE. For ARM, it splits block.
> +
> +static void vfio_dma_dirty_log_stop(struct vfio_iommu *iommu,
> + struct vfio_dma *dma)
> +{
> + struct vfio_domain *d;
> +
> + list_for_each_entry(d, >domain_list, next) {
> + /* Go through all domain anyway even if we fail */
> + iommu_merge_page(d->domain, dma->iova, dma->size,
> + d->prot | dma->prot);
> + }
> +}
Same as above comment, a generic interface is required here.
> +
> +static void vfio_iommu_dirty_log_switch(struct vfio_iommu *iommu, bool start)
> +{
> + struct rb_node *n;
> +
> + /* Split and merge even if all iommu don't support HWDBM now */
> + for (n = rb_first(>dma_list); n; n = rb_next(n)) {
> + struct vfio_dma *dma = rb_entry(n, struct vfio_dma, node);
> +
> + if (!dma->iommu_mapped)
> + continue;
> +
> + /* Go through all dma range anyway even if we fail */
> + if (start)
> + vfio_dma_dirty_log_start(iommu, dma);
> + else
> + vfio_dma_dirty_log_stop(iommu, dma);
> + }
> +}
> +
> static int vfio_iommu_type1_dirty_pages(struct vfio_iommu *iommu,
> unsigned long arg)
> {
> @@ -2812,8 +2900,10 @@ static int vfio_iommu_type1_dirty_pages(struct
> vfio_iommu *iommu,
> pgsize = 1 << __ffs(iommu->pgsize_bitmap);
> if (!iommu->dirty_page_tracking) {
> ret = vfio_dma_bitmap_alloc_all(iommu, pgsize);
> - if (!ret)
> + if (!ret) {
> iommu->dirty_page_tracking = true;
> + vfio_iommu_dirty_log_switch(iommu, true);
> + }
> }
> mutex_unlock(>lock);
> return ret;
> @@ -2822,6 +2912,7 @@ static int vfio_iommu_type1_dirty_pages(struct
> vfio_iommu *iommu,
> if (iommu->dirty_page_tracking) {
> iommu->dirty_page_tracking = false;
> vfio_dma_bitmap_free_all(iommu);
> + vfio_iommu_dirty_log_switch(iommu, false);
> }
> mutex_unlock(>lock);
> return 0;
> --
> 2.19.1
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