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

[David Vrabel]

On 09/04/14 15:21, Jan Beulich wrote:
>>>> On 09.04.14 at 16:06, <boris.ostrovsky@xxxxxxxxxx> wrote:
>> --- 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
> 
> I don't think it's guaranteed that this can't fault.

If loading %fs faults when it is restored previously, the fixup zeros
the value.  However, this later load could still fault even if the first
succeeded.

Suggest copying the fixup section from the RESTORE_REGS macros in
arch/x86/kernel/entry_32.S

David
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