The permission of vfio iommu is different and incompatible with vma
permission. If the iotlb->perm is IOMMU_NONE (e.g. qemu side), qemu will
simply call unmap ioctl() instead of mapping. Hence vfio_dma_map() can't
map a dma region with NONE permission.
This corner case will be exposed in coming virtio_fs cache_size
commit [1]
- mmap(NULL, size, PROT_NONE, MAP_ANONYMOUS | MAP_PRIVATE, -1, 0);
memory_region_init_ram_ptr()
- re-mmap the above area with read/write authority.
- vfio_dma_map() will be invoked when vfio device is hotplug added.
qemu:
vfio_listener_region_add()
vfio_dma_map(..., readonly=false)
map.flags is set to VFIO_DMA_MAP_FLAG_READ|VFIO_..._WRITE
ioctl(VFIO_IOMMU_MAP_DMA)
kernel:
vfio_dma_do_map()
vfio_pin_map_dma()
vfio_pin_pages_remote()
vaddr_get_pfn()
...
check_vma_flags() failed! because
vm_flags hasn't VM_WRITE && gup_flags
has FOLL_WRITE
It will report error in qemu log when hotplug adding(vfio) a nvme disk
to qemu guest on an Ampere EMAG server:
"VFIO_MAP_DMA failed: Bad address"
[1]
https://gitlab.com/virtio-fs/qemu/-/blob/virtio-fs-dev/hw/virtio/vhost-user-fs.c#L502
Signed-off-by: Jia He <justin...@arm.com>
---
drivers/vfio/vfio_iommu_type1.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/drivers/vfio/vfio_iommu_type1.c b/drivers/vfio/vfio_iommu_type1.c
index 67e827638995..33faa6b7dbd4 100644
--- a/drivers/vfio/vfio_iommu_type1.c
+++ b/drivers/vfio/vfio_iommu_type1.c
@@ -453,7 +453,8 @@ static int vaddr_get_pfn(struct mm_struct *mm, unsigned
long vaddr,
flags |= FOLL_WRITE;
mmap_read_lock(mm);
- ret = pin_user_pages_remote(mm, vaddr, 1, flags | FOLL_LONGTERM,
+ ret = pin_user_pages_remote(mm, vaddr, 1,
+ flags | FOLL_LONGTERM | FOLL_FORCE,
page, NULL, NULL);
if (ret == 1) {
*pfn = page_to_pfn(page[0]);
--
2.17.1
