[RFC PATCH v3 3/8] vfio/type1: Add an MMU notifier to avoid pinning
Alex Williamson
alex.williamson at redhat.com
Tue May 18 11:58:31 PDT 2021
On Fri, 9 Apr 2021 11:44:15 +0800
Shenming Lu <lushenming at huawei.com> wrote:
> To avoid pinning pages when they are mapped in IOMMU page tables, we
> add an MMU notifier to tell the addresses which are no longer valid
> and try to unmap them.
>
> Signed-off-by: Shenming Lu <lushenming at huawei.com>
> ---
> drivers/vfio/vfio_iommu_type1.c | 112 +++++++++++++++++++++++++++++++-
> 1 file changed, 109 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/vfio/vfio_iommu_type1.c b/drivers/vfio/vfio_iommu_type1.c
> index ab0ff60ee207..1cb9d1f2717b 100644
> --- a/drivers/vfio/vfio_iommu_type1.c
> +++ b/drivers/vfio/vfio_iommu_type1.c
> @@ -40,6 +40,7 @@
> #include <linux/notifier.h>
> #include <linux/dma-iommu.h>
> #include <linux/irqdomain.h>
> +#include <linux/mmu_notifier.h>
>
> #define DRIVER_VERSION "0.2"
> #define DRIVER_AUTHOR "Alex Williamson <alex.williamson at redhat.com>"
> @@ -69,6 +70,7 @@ struct vfio_iommu {
> struct mutex lock;
> struct rb_root dma_list;
> struct blocking_notifier_head notifier;
> + struct mmu_notifier mn;
> unsigned int dma_avail;
> unsigned int vaddr_invalid_count;
> uint64_t pgsize_bitmap;
> @@ -1204,6 +1206,72 @@ static long vfio_unmap_unpin(struct vfio_iommu *iommu, struct vfio_dma *dma,
> return unlocked;
> }
>
> +/* Unmap the IOPF mapped pages in the specified range. */
> +static void vfio_unmap_partial_iopf(struct vfio_iommu *iommu,
> + struct vfio_dma *dma,
> + dma_addr_t start, dma_addr_t end)
> +{
> + struct iommu_iotlb_gather *gathers;
> + struct vfio_domain *d;
> + int i, num_domains = 0;
> +
> + list_for_each_entry(d, &iommu->domain_list, next)
> + num_domains++;
> +
> + gathers = kzalloc(sizeof(*gathers) * num_domains, GFP_KERNEL);
> + if (gathers) {
> + for (i = 0; i < num_domains; i++)
> + iommu_iotlb_gather_init(&gathers[i]);
> + }
If we're always serialized on iommu->lock, would it make sense to have
gathers pre-allocated on the vfio_iommu object?
> +
> + while (start < end) {
> + unsigned long bit_offset;
> + size_t len;
> +
> + bit_offset = (start - dma->iova) >> PAGE_SHIFT;
> +
> + for (len = 0; start + len < end; len += PAGE_SIZE) {
> + if (!IOPF_MAPPED_BITMAP_GET(dma,
> + bit_offset + (len >> PAGE_SHIFT)))
> + break;
There are bitmap helpers for this, find_first_bit(),
find_next_zero_bit().
> + }
> +
> + if (len) {
> + i = 0;
> + list_for_each_entry(d, &iommu->domain_list, next) {
> + size_t unmapped;
> +
> + if (gathers)
> + unmapped = iommu_unmap_fast(d->domain,
> + start, len,
> + &gathers[i++]);
> + else
> + unmapped = iommu_unmap(d->domain,
> + start, len);
> +
> + if (WARN_ON(unmapped != len))
The IOMMU API does not guarantee arbitrary unmap sizes, this will
trigger and this exit path is wrong. If we've already unmapped the
IOMMU, shouldn't we proceed with @unmapped rather than @len so the
device can re-fault the extra mappings? Otherwise the IOMMU state
doesn't match the iopf bitmap state.
> + goto out;
> + }
> +
> + bitmap_clear(dma->iopf_mapped_bitmap,
> + bit_offset, len >> PAGE_SHIFT);
> +
> + cond_resched();
> + }
> +
> + start += (len + PAGE_SIZE);
> + }
> +
> +out:
> + if (gathers) {
> + i = 0;
> + list_for_each_entry(d, &iommu->domain_list, next)
> + iommu_iotlb_sync(d->domain, &gathers[i++]);
> +
> + kfree(gathers);
> + }
> +}
> +
> static void vfio_remove_dma(struct vfio_iommu *iommu, struct vfio_dma *dma)
> {
> WARN_ON(!RB_EMPTY_ROOT(&dma->pfn_list));
> @@ -3197,17 +3265,18 @@ static int vfio_iommu_type1_dma_map_iopf(struct iommu_fault *fault, void *data)
>
> vaddr = iova - dma->iova + dma->vaddr;
>
> - if (vfio_pin_page_external(dma, vaddr, &pfn, true))
> + if (vfio_pin_page_external(dma, vaddr, &pfn, false))
> goto out_invalid;
>
> if (vfio_iommu_map(iommu, iova, pfn, 1, dma->prot)) {
> - if (put_pfn(pfn, dma->prot))
> - vfio_lock_acct(dma, -1, true);
> + put_pfn(pfn, dma->prot);
> goto out_invalid;
> }
>
> bitmap_set(dma->iopf_mapped_bitmap, bit_offset, 1);
>
> + put_pfn(pfn, dma->prot);
> +
> out_success:
> status = IOMMU_PAGE_RESP_SUCCESS;
>
> @@ -3220,6 +3289,43 @@ static int vfio_iommu_type1_dma_map_iopf(struct iommu_fault *fault, void *data)
> return 0;
> }
>
> +static void mn_invalidate_range(struct mmu_notifier *mn, struct mm_struct *mm,
> + unsigned long start, unsigned long end)
> +{
> + struct vfio_iommu *iommu = container_of(mn, struct vfio_iommu, mn);
> + struct rb_node *n;
> + int ret;
> +
> + mutex_lock(&iommu->lock);
> +
> + ret = vfio_wait_all_valid(iommu);
> + if (WARN_ON(ret < 0))
> + return;
Is WARN_ON sufficient for this error condition? We've been told to
evacuate a range of mm, the device still has DMA access, we've removed
page pinning. This seems like a BUG_ON condition to me, we can't allow
the system to continue in any way with pages getting unmapped from
under the device.
> +
> + for (n = rb_first(&iommu->dma_list); n; n = rb_next(n)) {
> + struct vfio_dma *dma = rb_entry(n, struct vfio_dma, node);
> + unsigned long start_n, end_n;
> +
> + if (end <= dma->vaddr || start >= dma->vaddr + dma->size)
> + continue;
> +
> + start_n = ALIGN_DOWN(max_t(unsigned long, start, dma->vaddr),
> + PAGE_SIZE);
> + end_n = ALIGN(min_t(unsigned long, end, dma->vaddr + dma->size),
> + PAGE_SIZE);
> +
> + vfio_unmap_partial_iopf(iommu, dma,
> + start_n - dma->vaddr + dma->iova,
> + end_n - dma->vaddr + dma->iova);
> + }
> +
> + mutex_unlock(&iommu->lock);
> +}
> +
> +static const struct mmu_notifier_ops vfio_iommu_type1_mn_ops = {
> + .invalidate_range = mn_invalidate_range,
> +};
> +
> static long vfio_iommu_type1_ioctl(void *iommu_data,
> unsigned int cmd, unsigned long arg)
> {
Again, this patch series is difficult to follow because we're
introducing dead code until the mmu notifier actually has a path to be
registered. We shouldn't be taking any faults until iopf is enabled,
so it seems like we can add more of the core support alongside this
code.
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