Re: [PATCH v13 12/15] vfio: Allow reserved msi iova registration

Auger Eric
2016-10-07T17:11:43Z

Hi Alex,

On 06/10/2016 22:19, Alex Williamson wrote:
> On Thu, 6 Oct 2016 08:45:28 +0000
> Eric Auger <eric.auger-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org> wrote:
>
>> The user is allowed to register a reserved MSI IOVA range by using the
>> DMA MAP API and setting the new flag: VFIO_DMA_MAP_FLAG_MSI_RESERVED_IOVA.
>> This region is stored in the vfio_dma rb tree. At that point the iova
>> range is not mapped to any target address yet. The host kernel will use
>> those iova when needed, typically when MSIs are allocated.
>>
>> Signed-off-by: Eric Auger <eric.auger-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
>> Signed-off-by: Bharat Bhushan <Bharat.Bhushan-KZfg59tc24xl57MIdRCFDg@public.gmane.org>
>>
>> ---
>> v12 -> v13:
>> - use iommu_get_dma_msi_region_cookie
>>
>> v9 -> v10
>> - use VFIO_IOVA_RESERVED_MSI enum value
>>
>> v7 -> v8:
>> - use iommu_msi_set_aperture function. There is no notion of
>> unregistration anymore since the reserved msi slot remains
>> until the container gets closed.
>>
>> v6 -> v7:
>> - use iommu_free_reserved_iova_domain
>> - convey prot attributes downto dma-reserved-iommu iova domain creation
>> - reserved bindings teardown now performed on iommu domain destruction
>> - rename VFIO_DMA_MAP_FLAG_MSI_RESERVED_IOVA into
>> VFIO_DMA_MAP_FLAG_RESERVED_MSI_IOVA
>> - change title
>> - pass the protection attribute to dma-reserved-iommu API
>>
>> v3 -> v4:
>> - use iommu_alloc/free_reserved_iova_domain exported by dma-reserved-iommu
>> - protect vfio_register_reserved_iova_range implementation with
>> CONFIG_IOMMU_DMA_RESERVED
>> - handle unregistration by user-space and on vfio_iommu_type1 release
>>
>> v1 -> v2:
>> - set returned value according to alloc_reserved_iova_domain result
>> - free the iova domains in case any error occurs
>>
>> RFC v1 -> v1:
>> - takes into account Alex comments, based on
>> [RFC PATCH 1/6] vfio: Add interface for add/del reserved iova region:
>> - use the existing dma map/unmap ioctl interface with a flag to register
>> a reserved IOVA range. A single reserved iova region is allowed.
>> ---
>> drivers/vfio/vfio_iommu_type1.c | 77 ++++++++++++++++++++++++++++++++++++++++-
>> include/uapi/linux/vfio.h | 10 +++++-
>> 2 files changed, 85 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/vfio/vfio_iommu_type1.c b/drivers/vfio/vfio_iommu_type1.c
>> index 5bc5fc9..c2f8bd9 100644
>> --- a/drivers/vfio/vfio_iommu_type1.c
>> +++ b/drivers/vfio/vfio_iommu_type1.c
>> @@ -442,6 +442,20 @@ static void vfio_unmap_unpin(struct vfio_iommu *iommu, struct vfio_dma *dma)
>> vfio_lock_acct(-unlocked);
>> }
>>
>> +static int vfio_set_msi_aperture(struct vfio_iommu *iommu,
>> + dma_addr_t iova, size_t size)
>> +{
>> + struct vfio_domain *d;
>> + int ret = 0;
>> +
>> + list_for_each_entry(d, &iommu->domain_list, next) {
>> + ret = iommu_get_dma_msi_region_cookie(d->domain, iova, size);
>> + if (ret)
>> + break;
>> + }
>> + return ret;
>
> Doesn't this need an unwind on failure loop?
At the moment the de-allocation is done by the smmu driver, on
domain_free ops, which calls iommu_put_dma_cookie. In case,
iommu_get_dma_msi_region_cookie fails on a given VFIO domain currently
there is no other way but destroying all VFIO domains and redo everything.

So yes I plan to unfold everything, ie call iommu_put_dma_cookie for
each domain.
>
>> +}
>> +
>> static void vfio_remove_dma(struct vfio_iommu *iommu, struct vfio_dma *dma)
>> {
>> vfio_unmap_unpin(iommu, dma);
>> @@ -691,6 +705,63 @@ static int vfio_dma_do_map(struct vfio_iommu *iommu,
>> return ret;
>> }
>>
>> +static int vfio_register_msi_range(struct vfio_iommu *iommu,
>> + struct vfio_iommu_type1_dma_map *map)
>> +{
>> + dma_addr_t iova = map->iova;
>> + size_t size = map->size;
>> + int ret = 0;
>> + struct vfio_dma *dma;
>> + unsigned long order;
>> + uint64_t mask;
>> +
>> + /* Verify that none of our __u64 fields overflow */
>> + if (map->size != size || map->iova != iova)
>> + return -EINVAL;
>> +
>> + order = __ffs(vfio_pgsize_bitmap(iommu));
>> + mask = ((uint64_t)1 << order) - 1;
>> +
>> + WARN_ON(mask & PAGE_MASK);
>> +
>> + if (!size || (size | iova) & mask)
>> + return -EINVAL;
>> +
>> + /* Don't allow IOVA address wrap */
>> + if (iova + size - 1 < iova)
>> + return -EINVAL;
>> +
>> + mutex_lock(&iommu->lock);
>> +
>> + if (vfio_find_dma(iommu, iova, size, VFIO_IOVA_ANY)) {
>> + ret = -EEXIST;
>> + goto unlock;
>> + }
>> +
>> + dma = kzalloc(sizeof(*dma), GFP_KERNEL);
>> + if (!dma) {
>> + ret = -ENOMEM;
>> + goto unlock;
>> + }
>> +
>> + dma->iova = iova;
>> + dma->size = size;
>> + dma->type = VFIO_IOVA_RESERVED_MSI;
>> +
>> + ret = vfio_set_msi_aperture(iommu, iova, size);
>> + if (ret)
>> + goto free_unlock;
>> +
>> + vfio_link_dma(iommu, dma);
>> + goto unlock;
>> +
>> +free_unlock:
>> + kfree(dma);
>> +unlock:
>> + mutex_unlock(&iommu->lock);
>> + return ret;
>> +}
>> +
>> static int vfio_bus_type(struct device *dev, void *data)
>> {
>> struct bus_type **bus = data;
>> @@ -1064,7 +1135,8 @@ static long vfio_iommu_type1_ioctl(void *iommu_data,
>> } else if (cmd == VFIO_IOMMU_MAP_DMA) {
>> struct vfio_iommu_type1_dma_map map;
>> uint32_t mask = VFIO_DMA_MAP_FLAG_READ |
>> - VFIO_DMA_MAP_FLAG_WRITE;
>> + VFIO_DMA_MAP_FLAG_WRITE |
>> + VFIO_DMA_MAP_FLAG_RESERVED_MSI_IOVA;
>>
>> minsz = offsetofend(struct vfio_iommu_type1_dma_map, size);
>>
>> @@ -1074,6 +1146,9 @@ static long vfio_iommu_type1_ioctl(void *iommu_data,
>> if (map.argsz < minsz || map.flags & ~mask)
>> return -EINVAL;
>>
>> + if (map.flags & VFIO_DMA_MAP_FLAG_RESERVED_MSI_IOVA)
>> + return vfio_register_msi_range(iommu, &map);
>> +
>> return vfio_dma_do_map(iommu, &map);
>>
>> } else if (cmd == VFIO_IOMMU_UNMAP_DMA) {
>> diff --git a/include/uapi/linux/vfio.h b/include/uapi/linux/vfio.h
>> index 255a211..4a9dbc2 100644
>> --- a/include/uapi/linux/vfio.h
>> +++ b/include/uapi/linux/vfio.h
>> @@ -498,12 +498,19 @@ struct vfio_iommu_type1_info {
>> *
>> * Map process virtual addresses to IO virtual addresses using the
>> * provided struct vfio_dma_map. Caller sets argsz. READ &/ WRITE required.
>> + *
>> + * In case RESERVED_MSI_IOVA flag is set, the API only aims at registering an
>> + * IOVA region that will be used on some platforms to map the host MSI frames.
>> + * In that specific case, vaddr is ignored. Once registered, an MSI reserved
>> + * IOVA region stays until the container is closed.
>> */
>> struct vfio_iommu_type1_dma_map {
>> __u32 argsz;
>> __u32 flags;
>> #define VFIO_DMA_MAP_FLAG_READ (1 << 0) /* readable from device */
>> #define VFIO_DMA_MAP_FLAG_WRITE (1 << 1) /* writable from device */
>> +/* reserved iova for MSI vectors*/
>> +#define VFIO_DMA_MAP_FLAG_RESERVED_MSI_IOVA (1 << 2)
>> __u64 vaddr; /* Process virtual address */
>> __u64 iova; /* IO virtual address */
>> __u64 size; /* Size of mapping (bytes) */
>> @@ -519,7 +526,8 @@ struct vfio_iommu_type1_dma_map {
>> * Caller sets argsz. The actual unmapped size is returned in the size
>> * field. No guarantee is made to the user that arbitrary unmaps of iova
>> * or size different from those used in the original mapping call will
>> - * succeed.
>> + * succeed. Once registered, an MSI region cannot be unmapped and stays
>> + * until the container is closed.
>> */
>> struct vfio_iommu_type1_dma_unmap {
>> __u32 argsz;
>
> What happens when an x86 user does a mapping with this new flag set?
> It seems like we end up configuring everything just as we would on a
> platform requiring MSI mapping, including setting the domain MSI
> geometry. Should we be testing the MSI geometry flag on the iommu to
> see if this is supported? Surprisingly few things seem to check that
> flag.

Yes I need to test the capability first and return -EINVAL in case the
capability is not supported..

Thanks

Eric
>
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