On 07.05.2011, at 22:32, Dushyant Bansal wrote: > Hi, > > On patching 'mfmsr' instruction with 'lwz', guest exits when it tries to execute that 'lwz' instruction. I am looking for possible causes for this exit. > > Here are the details: > Initially, > pc: 0xc0019420, instruction: 0x7c0000a6 [mfmsr r0] > As this is a privileged instruction, this causes an exit. > > qemu-system-ppc-4443 [000] 19733.740013: kvm_book3s_exit: exit=0x700 | pc=0xc0019420 | inst=0x7c0000a6 | msr=0x1032 | dar=0xe1736a00 | srr1=0x100000000004d032 > qemu-system-ppc-4443 [000] 19733.740029: kvm_book3s_patch: return=0 | pc=0xc0019420 | inst=0x7c0000a6 | msr=0x1032 | new_inst=0x8000f05c > qemu-system-ppc-4443 [000] 19733.740030: kvm_ppc_instr: inst 2080374950 pc 0xc0019420 emulate 0 > qemu-system-ppc-4443 [000] 19733.740037: kvm_book3s_reenter: reentry r=1 | pc=0xc0019420 > > I patched this instruction with: > 0x8000f05c: lwz r0, -4096(offset of msr) > This instruction reads the 'msr' field of the magic page into register r0. > > Then, I do not increment the pc value, so the guest starts at the same pc which now points to the new patched instruction. > > This 'lwz' instruction is causing a exit due to 'BOOK3S_INTERRUPT_PROGRAM' (exit_nr: 0x700). > What could be the reason for this exit? As, 'lwz' is not a privileged instruction, I am unable to think of any reason. Did you flush the icache after you patched the instruction? See the function flush_icache_range. Without, your CPU still has the old instruction in its cache, making it trap again :). Alex -- To unsubscribe from this list: send the line "unsubscribe kvm-ppc" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
