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

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Message-Id: <1496448362-26558-4-git-send-email-ankur.a.arora@oracle.com>
Date:   Fri,  2 Jun 2017 17:06:00 -0700
From:   Ankur Arora <ankur.a.arora@...cle.com>
To:     linux-kernel@...r.kernel.org, xen-devel@...ts.xenproject.org
Cc:     boris.ostrovsky@...cle.com, jgross@...e.com,
        Ankur Arora <ankur.a.arora@...cle.com>
Subject: [PATCH 3/5] xen/pv: Fix OOPS on restore for a PV, !SMP domain

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@...cle.com>
Signed-off-by: Ankur Arora <ankur.a.arora@...cle.com>
---
 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