From: davem <davem@openbsd.org>
Date: Sun, 14 Jan 1996 00:39:18 +0000 (+0000)
Subject: The sun mmu is very broken, and we all can thank crashme for
X-Git-Url: http://artulab.com/gitweb/?a=commitdiff_plain;h=8d71c1d45f236c6efb0f749c2d53ba9433acf66a;p=openbsd

The sun mmu is very broken, and we all can thank crashme for
helping me find this bug.  On execution of an atomic load/store instruction
the chip will only say that a read fault is happening, we then load up a
readonly translation to the accessed page, and we get the fault again still
showing a read-fault.  We end up faulting in a loop forever and the process
appears to be completely stuck.  The algorithm to fix this problem goes like
this.  If we get a non-text fault, and the fault type is VM_PROT_READ, and
the SER_PROT bit is set in the syncronous fault error register, we take
a peek at the instruction at pc.  If this instruction is indeed an ldstub
or a swap variant we or in VM_PROT_WRITE to the fault type.
---

diff --git a/sys/arch/sparc/sparc/trap.c b/sys/arch/sparc/sparc/trap.c
index 2f6103499da..2925b0adea2 100644
--- a/sys/arch/sparc/sparc/trap.c
+++ b/sys/arch/sparc/sparc/trap.c
@@ -598,6 +598,22 @@ mem_access_fault(type, ser, v, pc, psr, tf)
 	if (VA_INHOLE(v))
 		goto fault;
 	ftype = ser & SER_WRITE ? VM_PROT_READ|VM_PROT_WRITE : VM_PROT_READ;
+	if(ftype == VM_PROT_READ && (ser & SER_PROT) && type != T_TEXTFAULT) {
+		/* If this is an ldstub or swap instruction
+		 * then we are about to fault in a loop forever
+		 * as only the read part of the fault will be
+		 * reported by the mmu.
+		 */
+		int error, insn;
+
+		error = copyin((caddr_t) pc, &insn, sizeof(int));
+		if(!error) {
+			insn = (insn >> 16); /* high word */
+			insn &= 0xc168;
+			if(insn == 0xc068)
+				ftype |= VM_PROT_WRITE;
+		}
+	}
 	va = trunc_page(v);
 	if (psr & PSR_PS) {
 		extern char Lfsbail[];