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/ To Unsubscribe: send mail to [EMAIL PROTECTED] with "unsubscribe freebsd-current" in the body of the message
