[PATCH 1/3] xen: check required Xen features

[Juergen Gross <jgross@xxxxxxxx>]

Linux kernel is not supported to run on Xen versions older than 4.0.

Add tests for required Xen features always being present in Xen 4.0
and newer.

Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
---
 drivers/xen/features.c | 18 ++++++++++++++++++
 1 file changed, 18 insertions(+)

diff --git a/drivers/xen/features.c b/drivers/xen/features.c
index 25c053b09605..60503299c9bc 100644
--- a/drivers/xen/features.c
+++ b/drivers/xen/features.c
@@ -9,13 +9,26 @@
 #include <linux/types.h>
 #include <linux/cache.h>
 #include <linux/export.h>
+#include <linux/printk.h>
 
 #include <asm/xen/hypercall.h>
 
+#include <xen/xen.h>
 #include <xen/interface/xen.h>
 #include <xen/interface/version.h>
 #include <xen/features.h>
 
+/*
+ * Linux kernel expects at least Xen 4.0.
+ *
+ * Assume some features to be available for that reason (depending on guest
+ * mode, of course).
+ */
+#define chk_feature(f) {                                               \
+               if (!xen_feature(f))                                    \
+                       pr_err("Xen: feature %s not available!\n", #f); \
+       }
+
 u8 xen_features[XENFEAT_NR_SUBMAPS * 32] __read_mostly;
 EXPORT_SYMBOL_GPL(xen_features);
 
@@ -31,4 +44,9 @@ void xen_setup_features(void)
                for (j = 0; j < 32; j++)
                        xen_features[i * 32 + j] = !!(fi.submap & 1<<j);
        }
+
+       if (xen_pv_domain()) {
+               chk_feature(XENFEAT_mmu_pt_update_preserve_ad);
+               chk_feature(XENFEAT_gnttab_map_avail_bits);
+       }
 }
-- 
2.26.2