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This commit is contained in:
Frans Kaashoek 2016-08-26 08:46:13 -04:00
parent 27ff70dc08
commit 37939f24c2
1 changed files with 3 additions and 1 deletions
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4
vm.c
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@ -168,7 +168,9 @@ switchuvm(struct proc *p)
cpu->gdt[SEG_TSS].s = 0;
cpu->ts.ss0 = SEG_KDATA << 3;
cpu->ts.esp0 = (uint)proc->kstack + KSTACKSIZE;
cpu->ts.iomb = (ushort) 0xFFFF; // forbid I/O instructions from user space
// setting IOPL=0 in eflags *and* iomb beyond the tss segment limit
// forbids I/O instructions (e.g., inb and outb) from user space
cpu->ts.iomb = (ushort) 0xFFFF;
ltr(SEG_TSS << 3);
if(p->pgdir == 0)
panic("switchuvm: no pgdir");