From 8d1f99637af48e28c0b4ebbe044e47abcefb5a5c Mon Sep 17 00:00:00 2001 From: Peter Froehlich Date: Thu, 22 Dec 2016 20:26:37 -0500 Subject: [PATCH] Fix long-standing switchuvm() inconsistency. switchuvm() is supposed to switch the TSS and page table to the process p it is passed. Alas, instead of using p to access the kstack field, it used the global proc. This worked fine because (a) most uses of switchuvm() pass proc anyway and (b) because in the schedule, where we call switchuvm with the newly scheduled process, we actually set the global proc before the call. But I think it's still a bug, even if it never broke a test case. :-) --- vm.c | 11 ++++++++--- 1 file changed, 8 insertions(+), 3 deletions(-) diff --git a/vm.c b/vm.c index 764512c..9db8b67 100644 --- a/vm.c +++ b/vm.c @@ -163,17 +163,22 @@ switchkvm(void) void switchuvm(struct proc *p) { + if(p == 0) + panic("switchuvm: no process"); + if(p->kstack == 0) + panic("switchuvm: no kstack"); + if(p->pgdir == 0) + panic("switchuvm: no pgdir"); + pushcli(); cpu->gdt[SEG_TSS] = SEG16(STS_T32A, &cpu->ts, sizeof(cpu->ts)-1, 0); cpu->gdt[SEG_TSS].s = 0; cpu->ts.ss0 = SEG_KDATA << 3; - cpu->ts.esp0 = (uint)proc->kstack + KSTACKSIZE; + cpu->ts.esp0 = (uint)p->kstack + KSTACKSIZE; // 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"); lcr3(V2P(p->pgdir)); // switch to process's address space popcli(); }