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Date: Thu, 22 Mar 2018 15:48:00 -0600
From: Alex Williamson <alex.williamson@...hat.com>
To: Suravee Suthikulpanit <suravee.suthikulpanit@....com>
Cc: kvm@...r.kernel.org, linux-kernel@...r.kernel.org, joro@...tes.org,
jroedel@...e.de
Subject: Re: [PATCH v5] vfio/type1: Adopt fast IOTLB flush interface when
unmap IOVAs
On Thu, 22 Feb 2018 15:59:15 -0700
Alex Williamson <alex.williamson@...hat.com> wrote:
> On Thu, 1 Feb 2018 01:27:38 -0500
> Suravee Suthikulpanit <suravee.suthikulpanit@....com> wrote:
>
> > VFIO IOMMU type1 currently upmaps IOVA pages synchronously, which requires
> > IOTLB flushing for every unmapping. This results in large IOTLB flushing
> > overhead when handling pass-through devices has a large number of mapped
> > IOVAs. This can be avoided by using the new IOTLB flushing interface.
> >
> > Cc: Alex Williamson <alex.williamson@...hat.com>
> > Cc: Joerg Roedel <joro@...tes.org>
> > Signed-off-by: Suravee Suthikulpanit <suravee.suthikulpanit@....com>
> > ---
> >
> > Changes from v4 (https://lkml.org/lkml/2018/1/31/153)
> > * Change return type from ssize_t back to size_t since we no longer
> > changing IOMMU API. Also update error handling logic accordingly.
> > * In unmap_unpin_fast(), also sync when failing to allocate entry.
> > * Some code restructuring and variable renaming.
> >
> > drivers/vfio/vfio_iommu_type1.c | 128 ++++++++++++++++++++++++++++++++++++----
> > 1 file changed, 117 insertions(+), 11 deletions(-)
> >
> > diff --git a/drivers/vfio/vfio_iommu_type1.c b/drivers/vfio/vfio_iommu_type1.c
> > index e30e29a..6041530 100644
> > --- a/drivers/vfio/vfio_iommu_type1.c
> > +++ b/drivers/vfio/vfio_iommu_type1.c
> > @@ -102,6 +102,13 @@ struct vfio_pfn {
> > atomic_t ref_count;
> > };
> >
> > +struct vfio_regions {
> > + struct list_head list;
> > + dma_addr_t iova;
> > + phys_addr_t phys;
> > + size_t len;
> > +};
> > +
> > #define IS_IOMMU_CAP_DOMAIN_IN_CONTAINER(iommu) \
> > (!list_empty(&iommu->domain_list))
> >
> > @@ -648,11 +655,102 @@ static int vfio_iommu_type1_unpin_pages(void *iommu_data,
> > return i > npage ? npage : (i > 0 ? i : -EINVAL);
> > }
> >
> > +static long vfio_sync_unpin(struct vfio_dma *dma, struct vfio_domain *domain,
> > + struct list_head *regions)
> > +{
> > + long unlocked = 0;
> > + struct vfio_regions *entry, *next;
> > +
> > + iommu_tlb_sync(domain->domain);
> > +
> > + list_for_each_entry_safe(entry, next, regions, list) {
> > + unlocked += vfio_unpin_pages_remote(dma,
> > + entry->iova,
> > + entry->phys >> PAGE_SHIFT,
> > + entry->len >> PAGE_SHIFT,
> > + false);
> > + list_del(&entry->list);
> > + kfree(entry);
> > + }
> > +
> > + cond_resched();
> > +
> > + return unlocked;
> > +}
> > +
> > +/*
> > + * Generally, VFIO needs to unpin remote pages after each IOTLB flush.
> > + * Therefore, when using IOTLB flush sync interface, VFIO need to keep track
> > + * of these regions (currently using a list).
> > + *
> > + * This value specifies maximum number of regions for each IOTLB flush sync.
> > + */
> > +#define VFIO_IOMMU_TLB_SYNC_MAX 512
> > +
> > +static size_t unmap_unpin_fast(struct vfio_domain *domain,
> > + struct vfio_dma *dma, dma_addr_t *iova,
> > + size_t len, phys_addr_t phys, long *unlocked,
> > + struct list_head *unmapped_list,
> > + int *unmapped_cnt)
> > +{
> > + size_t unmapped = 0;
> > + struct vfio_regions *entry = kzalloc(sizeof(*entry), GFP_KERNEL);
> > +
> > + if (entry) {
> > + unmapped = iommu_unmap_fast(domain->domain, *iova, len);
> > +
> > + if (!unmapped) {
> > + kfree(entry);
> > + } else {
> > + iommu_tlb_range_add(domain->domain, *iova, unmapped);
> > + entry->iova = *iova;
> > + entry->phys = phys;
> > + entry->len = unmapped;
> > + list_add_tail(&entry->list, unmapped_list);
> > +
> > + *iova += unmapped;
> > + (*unmapped_cnt)++;
> > + }
> > + }
> > +
> > + /*
> > + * Sync if the number of fast-unmap regions hits the limit
> > + * or in case of errors.
> > + */
> > + if (*unmapped_cnt >= VFIO_IOMMU_TLB_SYNC_MAX || !unmapped) {
> > + *unlocked += vfio_sync_unpin(dma, domain,
> > + unmapped_list);
> > + *unmapped_cnt = 0;
> > + }
> > +
> > + return unmapped;
> > +}
> > +
> > +static size_t unmap_unpin_slow(struct vfio_domain *domain,
> > + struct vfio_dma *dma, dma_addr_t *iova,
> > + size_t len, phys_addr_t phys,
> > + long *unlocked)
> > +{
> > + size_t unmapped = iommu_unmap(domain->domain, *iova, len);
> > +
> > + if (unmapped) {
> > + *unlocked += vfio_unpin_pages_remote(dma, *iova,
> > + phys >> PAGE_SHIFT,
> > + unmapped >> PAGE_SHIFT,
> > + false);
> > + *iova += unmapped;
> > + cond_resched();
> > + }
> > + return unmapped;
> > +}
> > +
> > static long vfio_unmap_unpin(struct vfio_iommu *iommu, struct vfio_dma *dma,
> > bool do_accounting)
> > {
> > dma_addr_t iova = dma->iova, end = dma->iova + dma->size;
> > struct vfio_domain *domain, *d;
> > + struct list_head unmapped_region_list;
> > + int unmapped_region_cnt = 0;
> > long unlocked = 0;
> >
> > if (!dma->size)
> > @@ -661,6 +759,8 @@ static long vfio_unmap_unpin(struct vfio_iommu *iommu, struct vfio_dma *dma,
> > if (!IS_IOMMU_CAP_DOMAIN_IN_CONTAINER(iommu))
> > return 0;
> >
> > + INIT_LIST_HEAD(&unmapped_region_list);
>
> Since I harassed Shameer about using LIST_HEAD() for the iova list
> extension, I feel obligated to note that it can also be used here. If
> you approve I'll just remove the above INIT_LIST_HEAD() and declare
> unmapped_region_list as LIST_HEAD(unmapped_region_list);, no need to
> re-send. Otherwise looks fine to me. Thanks,
I went ahead with this option, applied to vfio next branch for v4.17.
Thanks,
Alex
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