[Xen-devel] [PATCH 3/5] xen/pv: Fix OOPS on restore for a PV, !SMP domain

[Ankur Arora <ankur.a.arora@xxxxxxxxxx>]

If CONFIG_SMP is disabled, xen_setup_vcpu_info_placement() is called from
xen_setup_shared_info(). This is fine as far as boot goes, but it means
that we also call it in the restore path. This results in an OOPS
because we assign to pv_mmu_ops.read_cr2 which is __ro_after_init.

Also, though less problematically, this means we call xen_vcpu_setup()
twice at restore -- once from the vcpu info placement call and the
second time from xen_vcpu_restore().

Fix by calling xen_setup_vcpu_info_placement() at boot only.

Reviewed-by: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>
Signed-off-by: Ankur Arora <ankur.a.arora@xxxxxxxxxx>
---
 arch/x86/xen/enlighten_pv.c | 26 +++++++++++++++-----------
 1 file changed, 15 insertions(+), 11 deletions(-)

diff --git a/arch/x86/xen/enlighten_pv.c b/arch/x86/xen/enlighten_pv.c
index f51e48299692..29cad193db53 100644
--- a/arch/x86/xen/enlighten_pv.c
+++ b/arch/x86/xen/enlighten_pv.c
@@ -938,23 +938,27 @@ void xen_setup_shared_info(void)
                HYPERVISOR_shared_info =
                        (struct shared_info *)__va(xen_start_info->shared_info);
 
-#ifndef CONFIG_SMP
-       /* In UP this is as good a place as any to set up shared info */
-       xen_setup_vcpu_info_placement();
-#endif
-
        xen_setup_mfn_list_list();
 
-       /*
-        * Now that shared info is set up we can start using routines that
-        * point to pvclock area.
-        */
-       if (system_state == SYSTEM_BOOTING)
+       if (system_state == SYSTEM_BOOTING) {
+#ifndef CONFIG_SMP
+               /*
+                * In UP this is as good a place as any to set up shared info.
+                * Limit this to boot only, at restore vcpu setup is done via
+                * xen_vcpu_restore().
+                */
+               xen_setup_vcpu_info_placement();
+#endif
+               /*
+                * Now that shared info is set up we can start using routines
+                * that point to pvclock area.
+                */
                xen_init_time_ops();
+       }
 }
 
 /* This is called once we have the cpu_possible_mask */
-void xen_setup_vcpu_info_placement(void)
+void __ref xen_setup_vcpu_info_placement(void)
 {
        int cpu;
 
-- 
2.7.4


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