[Xen-devel] [PATCH v4 1/3] xen/arm: introduce XENFEAT_grant_map_identity

[Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>]

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@xxxxxxxxxxxxx>
Tested-by: Denis Schneider <v1ne2go@xxxxxxxxx>

---
Changes in v3:
- rename XENFEAT_grant_map_11 to XENFEAT_grant_map_identity.
---
 arch/arm/xen/enlighten.c         |    6 ++++++
 include/xen/interface/features.h |    3 +++
 2 files changed, 9 insertions(+)

diff --git a/arch/arm/xen/enlighten.c b/arch/arm/xen/enlighten.c
index b96723e..eef324f 100644
--- a/arch/arm/xen/enlighten.c
+++ b/arch/arm/xen/enlighten.c
@@ -262,6 +262,12 @@ static int __init xen_guest_init(void)
        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
diff --git a/include/xen/interface/features.h b/include/xen/interface/features.h
index 131a6cc..14334d0 100644
--- a/include/xen/interface/features.h
+++ b/include/xen/interface/features.h
@@ -53,6 +53,9 @@
 /* operation as Dom0 is supported */
 #define XENFEAT_dom0                      11
 
+/* Xen also maps grant references at pfn = mfn */
+#define XENFEAT_grant_map_identity        12
+
 #define XENFEAT_NR_SUBMAPS 1
 
 #endif /* __XEN_PUBLIC_FEATURES_H__ */
-- 
1.7.10.4


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