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grant_table_op v2 support for HVM?


I'm working on NetBSD Xen support.

Recently, we've switched to grant version 2 mainly for the improved
status handling, and eventually for copy-only subpage grant support,
which I'd like to experiment with in our netback driver. Currently we
don't need the 64-bit frame, which I found was reason to Linux was
switched over to v2 a while ago.

However, later found out that HVM doesn't actually seem to support the
GNTTABOP_get_status_frames hypercall, so had to fall back to v1 for
HVM. Code in xen/arch/x86/hvm/hypercall.c, which doesn't have any
handling in GNTTABOP_get_status_frames neither in Xen 4.11/4.12/4.13.

Can you advise which version should be used by Dom0/DomU kernels?

Is there some way to still use v2 with HVM? Possibly instead of using
the status frames, still use the old cmpxchg16 method on hdr.flags,
but as I understand hdr.flags is not used for GTF_reading and
GTF_writing in v2. I also see the set_version and get_version calls
are still supported even for HVM.

Understandably, we'd prefer to use same version for PV and HVM kernels.





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