Commit 4461bbc0 authored by Boris Ostrovsky's avatar Boris Ostrovsky Committed by David Vrabel
Browse files

x86/xen: Fix 32-bit PV guests's usage of kernel_stack 



Commit 198d208d ("x86: Keep
thread_info on thread stack in x86_32") made 32-bit kernels use
kernel_stack to point to thread_info. That change missed a couple of
updates needed by Xen's 32-bit 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().

With respect to the second issue, we don't need GET_THREAD_INFO()
anymore: we used it as an intermediate step to get to per_cpu xen_vcpu
and avoid referencing %fs. Now that we are going to use %fs anyway we
may as well go directly to xen_vcpu.

Signed-off-by: default avatarBoris Ostrovsky <boris.ostrovsky@oracle.com>
Signed-off-by: default avatarDavid Vrabel <david.vrabel@citrix.com>
parent d06eb3ee

arch/x86/xen/smp.c

+2 −1
Original line number Diff line number Diff line
@@ -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);

arch/x86/xen/xen-asm_32.S

+17 −8
Original line number Diff line number Diff line
@@ -75,6 +75,17 @@ ENDPROC(xen_sysexit) 
 * stack state in whatever form its in, we keep things simple by only

 * using a single register which is pushed/popped on the stack.

 */



.macro POP_FS

1:

	popw %fs

.pushsection .fixup, "ax"

2:	movw $0, (%esp)

	jmp 1b

.popsection

	_ASM_EXTABLE(1b,2b)

.endm



ENTRY(xen_iret)

	/* test eflags for special cases */

	testl $(X86_EFLAGS_VM | XEN_EFLAGS_NMI), 8(%esp)
@@ -83,15 +94,13 @@ ENTRY(xen_iret) 
	push %eax

	ESP_OFFSET=4	# bytes pushed onto stack



	/*

	 * Store vcpu_info pointer for easy access.  Do it this way to

	 * avoid having to reload %fs

	 */

	/* Store vcpu_info pointer for easy access */

#ifdef CONFIG_SMP

	GET_THREAD_INFO(%eax)

	movl %ss:TI_cpu(%eax), %eax

	movl %ss:__per_cpu_offset(,%eax,4), %eax

	mov %ss:xen_vcpu(%eax), %eax

	pushw %fs

	movl $(__KERNEL_PERCPU), %eax

	movl %eax, %fs

	movl %fs:xen_vcpu, %eax

	POP_FS

#else

	movl %ss:xen_vcpu, %eax

#endif

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