Hi David,
On 6/3/21 1:54 PM, David Gibson wrote:
On Tue, Jun 01, 2021 at 07:09:21PM +0800, Lu Baolu wrote:
Hi Jason,
On 2021/5/29 7:36, Jason Gunthorpe wrote:
/*
* Bind an user-managed I/O page table with the IOMMU
*
* Because user page table is untrusted, IOASID nesting must be enabled
* for this ioasid so the kernel can enforce its DMA isolation policy
* through the parent ioasid.
*
* Pgtable binding protocol is different from DMA mapping. The latter
* has the I/O page table constructed by the kernel and updated
* according to user MAP/UNMAP commands. With pgtable binding the
* whole page table is created and updated by userspace, thus different
* set of commands are required (bind, iotlb invalidation, page fault, etc.).
*
* Because the page table is directly walked by the IOMMU, the user
* must use a format compatible to the underlying hardware. It can
* check the format information through IOASID_GET_INFO.
*
* The page table is bound to the IOMMU according to the routing
* information of each attached device under the specified IOASID. The
* routing information (RID and optional PASID) is registered when a
* device is attached to this IOASID through VFIO uAPI.
*
* Input parameters:
* - child_ioasid;
* - address of the user page table;
* - formats (vendor, address_width, etc.);
*
* Return: 0 on success, -errno on failure.
*/
#define IOASID_BIND_PGTABLE _IO(IOASID_TYPE, IOASID_BASE + 9)
#define IOASID_UNBIND_PGTABLE _IO(IOASID_TYPE, IOASID_BASE + 10)
Also feels backwards, why wouldn't we specify this, and the required
page table format, during alloc time?
Thinking of the required page table format, perhaps we should shed more
light on the page table of an IOASID. So far, an IOASID might represent
one of the following page tables (might be more):
1) an IOMMU format page table (a.k.a. iommu_domain)
2) a user application CPU page table (SVA for example)
3) a KVM EPT (future option)
4) a VM guest managed page table (nesting mode)
This version only covers 1) and 4). Do you think we need to support 2),
Isn't (2) the equivalent of using the using the host-managed pagetable
then doing a giant MAP of all your user address space into it? But
maybe we should identify that case explicitly in case the host can
optimize it.
Conceptually, yes. Current SVA implementation just reuses the
application's cpu page table w/o map/unmap operations.
Best regards,
baolu
