Re: Handle kernel page faults using task gate

[Chuck Ebbert <76306.1226@compuserve.com>]

On Thu, 30 Jun 2005 at 09:11:01 +0200, Ingo Molnar wrote:

> * eliad lubovsky <eliadl@013.net> wrote:
> 
> > How do I clear the 'busy' bit?
> > I set my TSS descriptor with
> > __set_tss_desc(cpu, GDT_ENTRY_PAGE_FAULT_TSS, &pagefault_tss);
> 
> i suspect you have to clear the busy bit in the pagefault handler 
> itself. The CPU marks it as busy upon fault. I guess it would be OK to 
> just do the above __set_tss_desc() for _every_ pagefault, that too will 
> clear the busy bit, but you are probably better off just clearing that 
> bit manually:
> 
>     cpu_gdt_table[cpu][GDT_ENTRY_TSS].b &= 0xfffffdff;


  Tasks are not reentrant.  Clearing the busy bit could let a second
instance of the handler overwrite the stack of the current one.

  Since recursive page faults should never occur, this should be OK.
Each CPU needs its own TSS for concurrent fault handling on SMP, though.


--
Chuck