Re: possible CPU bug and request for Intel contacts

[Ingo Molnar <mingo@elte.hu>]

* Seth, Rohit <rohit.seth@intel.com> wrote:

> On a little different note, while running the 4G-4G kernel on our
> machine, we saw occasional hangs.  Those are root caused to the fact
> that this kernel was first chaging the stack pointer from virtual
> stack to kernel and then changing the CR3 to that of kernel.  Any
> interrupt between these two instructions will result in those hangs as
> the interruption handler will execute with user's CR3(as the kernel
> thinks that it is already in kernel because of the value of esp). 
> Swapping the order, first loading the CR3 with kernel and then
> switching the stack to kernel fixes this issue.  Venki will generate
> that patch and send to lkml.

i'm not sure what you mean. Here's the relevant 4:4 code from Fedora:

#define __SWITCH_KERNELSPACE                            \
...
        movl %edx, %cr3;                                \
        movl %ebx, %esp;                                \

i.e. we _first_ load cr3 with the kernel pagetable value, then do we
switch esp to the real kernel stack.

	Ingo