[Xen-devel] [PATCH] x86/xen: Fix 32-bit PV guests's usage of kernel_stack

[Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>]

Commit 198d208df4371734ac4728f69cb585c284d20a15 made 32-bit kernels use
kernel_stack to point to thread_info. That change missed a couple of
updates needed by Xen's PV guests:

1. kernel_stack needs to be initialized for secondary CPUs
2. GET_THREAD_INFO() now uses %fs register which may not be the kernel's
version when executing xen_iret()

Signed-off-by: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>
---
 arch/x86/xen/smp.c        |    3 ++-
 arch/x86/xen/xen-asm_32.S |    4 ++++
 2 files changed, 6 insertions(+), 1 deletion(-)

diff --git a/arch/x86/xen/smp.c b/arch/x86/xen/smp.c
index a18eadd..7005974 100644
--- a/arch/x86/xen/smp.c
+++ b/arch/x86/xen/smp.c
@@ -441,10 +441,11 @@ static int xen_cpu_up(unsigned int cpu, struct 
task_struct *idle)
        irq_ctx_init(cpu);
 #else
        clear_tsk_thread_flag(idle, TIF_FORK);
+#endif
        per_cpu(kernel_stack, cpu) =
                (unsigned long)task_stack_page(idle) -
                KERNEL_STACK_OFFSET + THREAD_SIZE;
-#endif
+
        xen_setup_runstate_info(cpu);
        xen_setup_timer(cpu);
        xen_init_lock_cpu(cpu);
diff --git a/arch/x86/xen/xen-asm_32.S b/arch/x86/xen/xen-asm_32.S
index 33ca6e4..d433637 100644
--- a/arch/x86/xen/xen-asm_32.S
+++ b/arch/x86/xen/xen-asm_32.S
@@ -88,7 +88,11 @@ ENTRY(xen_iret)
         * avoid having to reload %fs
         */
 #ifdef CONFIG_SMP
+       pushw %fs
+       movl $(__KERNEL_PERCPU), %eax
+       movl %eax, %fs
        GET_THREAD_INFO(%eax)
+       popw %fs
        movl %ss:TI_cpu(%eax), %eax
        movl %ss:__per_cpu_offset(,%eax,4), %eax
        mov %ss:xen_vcpu(%eax), %eax
-- 
1.7.10.4


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