Mailing List Archive

Hello,

I find a strange behavior. When a machine is slow (or with many debug
traces or a qemu vm),
a interrupt can occur between the pv_irq_ops initialization and the xen_vcpu[0]
initialization. This lead to a problem because some operations in
xen_irq_ops use
xen_vcpu.
I send you a patch to fix that but I'm not quite sure that is the
right solution.

Regards,
Anthoine

From ac683ad8264f83fa0a5d743e18c0422e43e871d2 Mon Sep 17 00:00:00 2001
From: Anthoine Bourgeois <anthoine.bourgeois@gmail.com>
Date: Wed, 23 Nov 2011 19:23:42 +0100
Subject: [PATCH] Initialize xen_vcpu0 before initialize irq_ops.

xen_vcpu is used by
xen_irq_ops.xen_{save_fl,restore_fl,irq_disable,irq_enable} and should
be initialized before xen_init_irq_ops that initialize the pv_irq_ops
with it. If not, a call to those functions could lead to a deference of
NULL pointer. This behaviour was find with a slow machine or qemu.
---
arch/x86/xen/enlighten.c | 7 ++++---
1 files changed, 4 insertions(+), 3 deletions(-)

diff --git a/arch/x86/xen/enlighten.c b/arch/x86/xen/enlighten.c
index 2d69617..a8111a0 100644
--- a/arch/x86/xen/enlighten.c
+++ b/arch/x86/xen/enlighten.c
@@ -1166,6 +1166,10 @@ asmlinkage void __init xen_start_kernel(void)
*/
xen_setup_stackprotector();

+ /* Don't do the full vcpu_info placement stuff until we have a
+ possible map and a non-dummy shared_info. */
+ per_cpu(xen_vcpu, 0) = &HYPERVISOR_shared_info->vcpu_info[0];
+
xen_init_irq_ops();
xen_init_cpuid_mask();

@@ -1207,9 +1211,6 @@ asmlinkage void __init xen_start_kernel(void)
__supported_pte_mask &= ~(_PAGE_PWT | _PAGE_PCD);

__supported_pte_mask |= _PAGE_IOMAP;
- /* Don't do the full vcpu_info placement stuff until we have a
- possible map and a non-dummy shared_info. */
- per_cpu(xen_vcpu, 0) = &HYPERVISOR_shared_info->vcpu_info[0];

local_irq_disable();
early_boot_irqs_disabled = true;
--
1.7.3.4