Messages in this thread | | | Date | Wed, 09 Apr 2014 12:15:48 -0400 | From | Boris Ostrovsky <> | Subject | Re: [PATCH] x86/xen: Fix 32-bit PV guests's usage of kernel_stack |
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On 04/09/2014 11:25 AM, Steven Rostedt wrote: > On Wed, 09 Apr 2014 11:12:33 -0400 > Boris Ostrovsky <boris.ostrovsky@oracle.com> wrote: > >> 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@oracle.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 > Looks like this patch makes the above comment incorrect.
I didn't notice this (it was full 3 lines above the change), it will obviously have to be updated.
>> */ >> #ifdef CONFIG_SMP >> + pushw %fs >> + movl $(__KERNEL_PERCPU), %eax >> + movl %eax, %fs >> GET_THREAD_INFO(%eax) >> + popw %fs >> movl %ss:TI_cpu(%eax), %eax > Hmm, you're using GET_THREAD_INFO() to get the thread info to find the > current CPU for later use to avoid using %fs. ?? > > Is it possible to just push the cpu on the kernel irq stack and be able > to retrieve it manually? Looks like the only reason to use the > thread_info here is to get to the CPU index for below.
Or vcpu_info, which is what we are really after.
However, it looks like using %fs/GET_THREAD_INFO() should be OK as well, provided I deal with a potential faulting.
-boris
> >> movl %ss:__per_cpu_offset(,%eax,4), %eax >> mov %ss:xen_vcpu(%eax), %eax > -- Steve >
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