From owner-freebsd-smp  Sat Sep 26 03:09:48 1998
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To: freebsd-smp@FreeBSD.ORG
cc: jlemon@FreeBSD.ORG, yokota@zodiac.mech.utsunomiya-u.ac.jp
Subject: VM86 on SMP
Date: Sat, 26 Sep 1998 19:10:43 +0900
From: Kazutaka YOKOTA <yokota@zodiac.mech.utsunomiya-u.ac.jp>
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I compiled a SMP kernel with VM86.
It appears that the kernel panics as soon as something makes a vm86 call.

Example 1:
Enable apm0, then the kernel panics while apm0 is probed.

Trap 12
fault virtual address: 0xa00
fault code: superviser write

vm86_prepcall() at vm86_prepcall+0x4a
vm86_bioscall() at vm86_bioscall+0xe4
apmprobe() at apmprobe+0x3d

movl %eax,0(%edx,0) at vm86_prepcall+0x4a

Example 2:
Boot the kernel without APM, then try to load the VESA LKM. 
The same panic at the same place.

vm86_prepcall() at vm86_prepcall+0x4a
vm86_bioscall() at vm86_bioscall+0xe4

But, this time it is the VESA LKM initialization routine which is
calling VM86.

The uniprocessor kernel has, of cource, no problems in the above
situations.

I think the fault is at the following line. We have a hardcoded
address here: 0xa00, Is this address valid in SMP?

vm86_prepcall(struct vm86frame vmf)
{
        uintptr_t addr[] = { 0xA00, 0x1000 };   /* code, stack */
        u_char intcall[] = {
                CLI, INTn, 0x00, STI, HLT
        };

        if ((vmf.vmf_trapno & PAGE_MASK) <= 0xff) {
                /*interrupt call requested */
                intcall[2] = (u_char)(vmf.vmf_trapno & 0xff);
                memcpy((void *)addr[0], (void *)intcall, sizeof(intcall));
		~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
                vmf.vmf_ip = addr[0];
                vmf.vmf_cs = 0;
        }
        vmf.vmf_sp = addr[1] - 2;              /* keep aligned */
        vmf.kernel_es = vmf.kernel_ds = 0;
        vmf.vmf_ss = 0;
        vmf.vmf_eflags = PSL_VIF | PSL_VM | PSL_USER;
        vm86_initflags(&vmf);
}

Kazu

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