From mboxrd@z Thu Jan 1 00:00:00 1970 From: Dushyant Bansal Date: Mon, 09 May 2011 10:46:18 +0000 Subject: Re: Patching guest kernel code for better performance from HOST Message-Id: <4DC7C32A.3030501@cse.iitd.ac.in> List-Id: References: <4D9AD9E7.20904@cse.iitd.ac.in> In-Reply-To: <4D9AD9E7.20904@cse.iitd.ac.in> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: kvm-ppc@vger.kernel.org On Sunday 08 May 2011 02:22 AM, Alexander Graf wrote: > 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 :). Thanks. I tried flush_icache_range((ulong)pc, (ulong)pc + 4); The system becomes unresponsive and I have to use force shut down. Here, pc will have the address of guest instruction and flush_icache_range is called from host. Maybe, I am not using flush_icache_range in the correct way. Also, my host os is ppc64 and the guest is ppc32. I also tried: flush_cache_all() But the instruction is still present in the instruction cache. Dushyant