[Xen-devel] RE: [PATCH] Fixing stack alignment in x86-64 Xen

["Nakajima, Jun" <jun.nakajima@xxxxxxxxx>]

Andi Kleen wrote:
> "Nakajima, Jun" <jun.nakajima@xxxxxxxxx> writes:
>> 
>> The recent optimization reset_stack_and_jump() code needs to know the
>> exact address of the interrupt stack (because it resets %rsp), and
>> calculates it based on the value that Xen set (i.e. 8-byte boundary).
>> Since the processor forces the rsp0 on a 16-byte boundary (i.e.
>> moves it down by 8 bytes), Xen sees a wrong stack when returning
>> from the interrupt.
> 
> I would rather fix reset_stack_and_jump then to do the necessary
> rounding or better look at the original RSP the processor stored into
> the stack frame. Otherwise the 16 byte alignment will probably bite
> you later again.
> 
> -Andi

I think the right thing is to get rsp0 in TSS on a 16-byte boundary by
getting get_stack_bottom() and get_cpu_user_regs() see the correct
stack. That will fix the reset_stack_and_jump() as well. It's basically
what my patch does. 

Jun

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