xen/arm: introduce XENFEAT_grant_map_identity
The flag tells us that the hypervisor maps a grant page to guest
physical address == machine address of the page in addition to the
normal grant mapping address. It is needed to properly issue cache
maintenance operation at the completion of a DMA operation involving a
foreign grant.
Signed-off-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
Tested-by: Denis Schneider <v1ne2go@gmail.com>
diff --git a/arch/arm/xen/enlighten.c b/arch/arm/xen/enlighten.c
index 98544c5..0e15f01 100644
--- a/arch/arm/xen/enlighten.c
+++ b/arch/arm/xen/enlighten.c
@@ -260,6 +260,12 @@
xen_domain_type = XEN_HVM_DOMAIN;
xen_setup_features();
+
+ if (!xen_feature(XENFEAT_grant_map_identity)) {
+ pr_warn("Please upgrade your Xen.\n"
+ "If your platform has any non-coherent DMA devices, they won't work properly.\n");
+ }
+
if (xen_feature(XENFEAT_dom0))
xen_start_info->flags |= SIF_INITDOMAIN|SIF_PRIVILEGED;
else