--- John Baldwin <[EMAIL PROTECTED]> wrote:
> On 07-Jul-2002 Jonathan Lemon wrote:
> > On Sat, Jul 06, 2002 at 11:59:50PM -0700, David Xu wrote:
> >> Jonthan,
> >> 
> >>   I just use DOS program as an example, for any program, if it wants to go
> >> into VM86 mode, it is very easy, just calls i386_vm86() to initailize its
> >> VM86 pcb extension, setups some memory area, then call sigreturn() to turn
> >> into VM86 mode.
> >>   I think global in_vm86call flags is a bug under SMP, it creates a race
> >> condition. suppose this scenario:
> >>   CPU A is running a simple VM86 code program.
> >>   CPU B is running vm86_intcall() by some kernel driver (vesa module ?)
> >>   CPU B set in_vm86call = 1
> >>   CPU A gets a fault trap.
> >>   CPU A runs trap(), and find that in_vm86call is set and handles the trap
> >>         as  it is running vm86_intcall(), but it is not true and make a
> mess.
> > 
> > Yes, as I mentioned earlier, the way the original vm86 bioscall worked 
> > was to prevent an AST until the BIOS was done.  This relied on the giant
> > lock for correctness, since we only allowed one CPU into the kernel at 
> > once.  There probably needs to be some work done for -current in this area.
> Since vm86_lock is a spin lock, you could possibly make in_vm86call per-cpu
> or you could just check the lock instead of the variable to fix this.
> -- 
> John Baldwin <[EMAIL PROTECTED]>  <><  http://www.FreeBSD.org/~jhb/
> "Power Users Use the Power to Serve!"  -  http://www.FreeBSD.org/

when did the vm86_lock become spin lock ? I havn't seen changes in cvs,
it is still a MTX_DEF. I had tried changing it to spin lock and got a 
panic. :(

David Xu

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