[Xen-devel] [PATCH v2 5/5] xen: select grant interface version

[Juergen Gross <jgross@xxxxxxxx>]

Grant v2 will be needed in cases where a frame number in the grant
table can exceed 32 bits. For PV guests this is a host feature, while
for HVM guests this is a guest feature.

So select grant v2 in case frame numbers can be larger than 32 bits
and grant v1 else.

For testing purposes add a way to specify the grant interface version
via a boot parameter.

Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
---
V2:
- use cpuid on pv and max_possible_pfn on hvm for version select
---
 drivers/xen/grant-table.c | 35 +++++++++++++++++++++++++++++++++--
 1 file changed, 33 insertions(+), 2 deletions(-)

diff --git a/drivers/xen/grant-table.c b/drivers/xen/grant-table.c
index 573e7fe9b147..fa152832e0e6 100644
--- a/drivers/xen/grant-table.c
+++ b/drivers/xen/grant-table.c
@@ -33,6 +33,7 @@
 
 #define pr_fmt(fmt) "xen:" KBUILD_MODNAME ": " fmt
 
+#include <linux/bootmem.h>
 #include <linux/sched.h>
 #include <linux/mm.h>
 #include <linux/slab.h>
@@ -43,6 +44,7 @@
 #include <linux/hardirq.h>
 #include <linux/workqueue.h>
 #include <linux/ratelimit.h>
+#include <linux/moduleparam.h>
 
 #include <xen/xen.h>
 #include <xen/interface/xen.h>
@@ -52,6 +54,9 @@
 #include <xen/hvc-console.h>
 #include <xen/swiotlb-xen.h>
 #include <xen/balloon.h>
+#ifdef CONFIG_X86
+#include <asm/xen/cpuid.h>
+#endif
 #include <asm/xen/hypercall.h>
 #include <asm/xen/interface.h>
 
@@ -68,6 +73,8 @@ static int gnttab_free_count;
 static grant_ref_t gnttab_free_head;
 static DEFINE_SPINLOCK(gnttab_list_lock);
 struct grant_frames xen_auto_xlat_grant_frames;
+static unsigned int xen_gnttab_version;
+module_param_named(version, xen_gnttab_version, uint, 0);
 
 static union {
        struct grant_entry_v1 *v1;
@@ -1177,12 +1184,36 @@ static const struct gnttab_ops gnttab_v2_ops = {
        .query_foreign_access           = gnttab_query_foreign_access_v2,
 };
 
+static bool gnttab_need_v2(void)
+{
+#ifdef CONFIG_X86
+       uint32_t base, width;
+
+       if (xen_pv_domain()) {
+               base = xen_cpuid_base();
+               if (cpuid_eax(base) < 5)
+                       return false;   /* Information not available, use V1. */
+               width = cpuid_ebx(base + 5) &
+                       XEN_CPUID_MACHINE_ADDRESS_WIDTH_MASK;
+               return width > 32 + PAGE_SHIFT;
+       }
+#endif
+       return !!(max_possible_pfn >> 32);
+}
+
 static void gnttab_request_version(void)
 {
-       int rc;
+       long rc;
        struct gnttab_set_version gsv;
 
-       gsv.version = 1;
+       if (gnttab_need_v2())
+               gsv.version = 2;
+       else
+               gsv.version = 1;
+
+       /* Boot parameter overrides automatic selection. */
+       if (xen_gnttab_version >= 1 && xen_gnttab_version <= 2)
+               gsv.version = xen_gnttab_version;
 
        rc = HYPERVISOR_grant_table_op(GNTTABOP_set_version, &gsv, 1);
        if (rc == 0 && gsv.version == 2)
-- 
2.12.3


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