i386/86380: i386_set_ioperm doesn't take effect immediately

[Trevor Blackwell]

>Number:         86380
>Category:       i386
>Synopsis:       i386_set_ioperm doesn't take effect immediately
>Confidential:   no
>Severity:       serious
>Priority:       low
>Responsible:    freebsd-i386
>State:          open
>Quarter:        
>Keywords:       
>Date-Required:
>Class:          sw-bug
>Submitter-Id:   current-users
>Arrival-Date:   Tue Sep 20 19:10:02 GMT 2005
>Closed-Date:
>Last-Modified:
>Originator:     Trevor Blackwell
>Release:        FreeBSD 5.4-RELEASE-p6 i386
>Organization:
Anybots Inc
>Environment:

System: FreeBSD lab.anybots.com 5.4-RELEASE-p6 FreeBSD 5.4-RELEASE-p6 #0: Thu Sep 15 12:26:46 PDT 2005 root at tlb.anybots.com:/usr/obj/usr/src/sys/LAB i386


>Description:

Calling i386_set_ioperm immediately followed by an inb or outb causes a bus error. Inserting a context switch delay between the two
avoids the problem

>How-To-Repeat:

cat >t_ioperm.c <<EOF
#include <stdio.h>
#include <stdlib.h>
#include <sys/types.h>
#include <machine/sysarch.h>
#include <machine/cpufunc.h>

void
test_ioperm(int base, int len, int wr, int delay)
{
  if (i386_set_ioperm(base, len, 1)<0) {
    fprintf(stderr, "Can't set ioperm on %d %d\n", base, len);
    exit(1);
  }
  if (delay) {
    usleep(2000); // FreeBSD 5.4 seems to sometimes get a bus error if we do IO too soon after set_ioperm
  }
  if (wr) {
    outb(base, 0x00);
  } else {
    inb(base);
  }
}

int
main(int argc, char **argv)
{
  test_ioperm(atoi(argv[1]), atoi(argv[2]), atoi(argv[3]), atoi(argv[4]));
  return 0;
}

EOF

gcc -o t_ioperm t_ioperm.c
sudo ./t_ioperm 1018 8 0 0   # expect bus error
sudo ./t_ioperm 1018 8 0 1   # no bus error

(the port number is byte 2 of COM1, a fairly harmless thing to read from)

>Fix:

Inserting a usleep after i386_set_ioperm seems to work around it.
I assume there's some fancy lazy updating going on in the TLB management.
This happens for me on multiple machines, including a dual Xeon, a P4, and an old Pentium-MMX

-- 
Trevor Blackwell      tlb at tlb.org          (650) 776-7870


>Release-Note:
>Audit-Trail:
>Unformatted: