linux-kernel - [PATCH] x86/xen: Fix 32-bit PV guests's usage of kernel

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Date:	Wed,  9 Apr 2014 10:06:41 -0400
From:	Boris Ostrovsky <boris.ostrovsky@...cle.com>
To:	konrad.wilk@...cle.com, david.vrabel@...rix.com
Cc:	xen-devel@...ts.xenproject.org, linux-kernel@...r.kernel.org,
	srostedt@...hat.com, boris.ostrovsky@...cle.com
Subject: [PATCH] x86/xen: Fix 32-bit PV guests's usage of kernel_stack

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@...cle.com>
---
 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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