[PATCH v1 0/1] xen: mapcache: grants: Fix mixup betwen ro and rw mappings

["Edgar E. Iglesias" <edgar.iglesias@xxxxxxxxx>]

From: "Edgar E. Iglesias" <edgar.iglesias@xxxxxxx>

This fixes an issue with grant mappings when a read-only
mapping is requested followed by a read-write mapping for
the same page. Today, we don't track write-ability and
read-write lookups hit on read-only entries.

This series is an attempt to fix this by splitting mapcache_grants
in two, a read-only and a read-write instance.

I tried a couple of other approaches, one was to speculatively
map grants as read-write and if mapping fails, then fall back
to read-only. This works but since Xen logs each failed grant
mapping, it gets noisy.

Another way is to track writeability per mapping in the cache
and modify the lookup logic to only hit on compatible mappings.
It works but adds more complexity to the lookup logic compared
with the split cache approach.
https://gitlab.com/edgar.iglesias/qemu/-/commits/edgar/grants-ro-rw-fix

Cheers,
Edgar

Edgar E. Iglesias (1):
  xen: mapcache: Split mapcache_grants by ro and rw

 hw/xen/xen-mapcache.c | 26 +++++++++++++++++++-------
 1 file changed, 19 insertions(+), 7 deletions(-)

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2.43.0