On 7/30/26 12:34, Peter Maydell wrote:
On Thu, 30 Jul 2026 at 11:27, Michael S. Tsirkin <[email protected]> wrote:
On Thu, Jul 30, 2026 at 10:24:32AM +0100, Peter Maydell wrote:
The idea is rather just to ignore the unaligned-access-to-not-RAM
case as "only a theoretical issue" and default it to memmove().
If anybody reports an actual problem we can think about it then :-)
Well given the only reported case of virtio DMA into vfio memory we have is
GH100 and that one is mapped MT_NORMAL, I'm fine with that.
I feel extending vfio to report the mapping type to userspace might
not be a bad idea down the road, though. "Directly accessible"
is a very rough approximation to the rich variety of mappings
available across architectures.
Yes, this sounds like a good longer term idea. If userspace doesn't
have a way to know what the mapping behind something it's mmap()ed
is then it can't know what operations it can and can't safely do.
Gavin, didn't you have the idea of using a VFIO region caps for that ?
This is similar to what we did on POWER9 with :
VFIO_REGION_INFO_CAP_NVLINK2_SSATGT
which exported GPU RAM to the userspace too.
Thanks,
C.
