Re: Software breakpoint in kvmppc guest debug
Am 10.11.2010 04:39, Alexander Graf wrote: On 10.11.2010, at 04:31, Yoder Stuart-B08248 wrote: -Original Message- From: kvm-ppc-ow...@vger.kernel.org [mailto:kvm-ppc-ow...@vger.kernel.org] On Behalf Of Alexander Graf Sent: Tuesday, November 09, 2010 12:50 PM To: Wood Scott-B07421 Cc: Hollis Blanchard; Liu Yu-B13201; kvm-ppc@vger.kernel.org; Jan Kiszka Subject: Re: Software breakpoint in kvmppc guest debug On 09.11.2010, at 19:43, Scott Wood wrote: On Tue, 9 Nov 2010 19:26:25 +0100 Alexander Graf ag...@suse.de wrote: On 09.11.2010, at 19:17, Scott Wood wrote: On Tue, 9 Nov 2010 18:14:31 +0100 Alexander Graf ag...@suse.de wrote: Now, if we can get away with not using an undefined instruction (be it sc 64 or trap) I don't know. I'm not even sure we can get away with trap. Basically, WARN_ON should also trigger a trap, so you'd end up in gdb for that when having a breakpoint defined. There'd need to be a way for qemu/gdb to have KVM reflect the exception to the guest if it doesn't have a breakpoint on file for that address. Yes, but that piece is missing for every KVM target right now. I'd like to see something generic emerge here that we can reuse across different architectures :). We should try to define something that will make sense on other architectures, to whatever extent is practical -- but that doesn't mean we need to wait for them to act first. :-) Oh, I agree. I'm saying we should have Jan in the discussion :). Trap seems very tricky too though. According to page 1082 of the 2.06 spec, trap can issue a debug or a program interrupt depending on MSR_DE. I don't see any mentioning in the spec that we intercept program or debug interrupts. So I guess we'd have to override the offset vectors and handle _every_ interrupt ourselves. Bleks. Program and debug interrupts always go to the hypervisor. Only the exceptions for which GIVORs are defined (DSI, ISI, external IRQ, syscall, TLB miss) can go directly to the guest, and even those are generally optional based on EPCR. Ah, so it's a positive list. I guess I missed that part :). Thanks for the clarification. So making it a trap instruction for now should be ok. Let's align the code to the same x86 looks like for now. In the meanwhile, let's discuss with Jan on how to get a list of patched IPs into the kernel and implement that on top of the code we'll have aligned with x86 by then :). What about using the ehpriv instruction (defined in 2.06)? We could define a unique qemu software breakpoint, and the hypervisor's ehpriv handler will be able to easily distinguish them. On e500v2, this would be an illegal instruction. We don't need to worry about a conflict with future opcodes and it seems like the whole point of ehpriv being defined-- to let a hypervisor define special opcodes for stuff like this. Yes, it even states so in the little box below the description. Very good catch! If we use trap, we will need the list of patched IPs in the kernel. ehpriv avoids the need for that. Well, the way it's handled on x86 now is that the kernel asks user space if it knows about the breakpoint and if not user space reinjects the debug interrupt into the guest. Right. That's fine for x86 as we have a dedicated soft BP instruction. It's shared with the guest, but as long as the latter does not start using it heavily for whatever purpose, this lengthy loop to find the trap reason is OK. It avoids dispatching tables in the kernel. Still, if it actually turns out that PowerPC (or some other arch) needs this for performance reasons as no proper instructions could be defined, we should probably introduce a generic service to set a soft BP dispatching table in the kernel. That could also be used by x86 then, even though the practical improvement would be minimal there. Jan -- Siemens AG, Corporate Technology, CT T DE IT 1 Corporate Competence Center Embedded Linux -- To unsubscribe from this list: send the line unsubscribe kvm-ppc in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: Software breakpoint in kvmppc guest debug
On Tue, 9 Nov 2010 18:14:31 +0100 Alexander Graf ag...@suse.de wrote: Now, if we can get away with not using an undefined instruction (be it sc 64 or trap) I don't know. I'm not even sure we can get away with trap. Basically, WARN_ON should also trigger a trap, so you'd end up in gdb for that when having a breakpoint defined. There'd need to be a way for qemu/gdb to have KVM reflect the exception to the guest if it doesn't have a breakpoint on file for that address. -Scott -- To unsubscribe from this list: send the line unsubscribe kvm-ppc in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: Software breakpoint in kvmppc guest debug
On 09.11.2010, at 19:17, Scott Wood wrote: On Tue, 9 Nov 2010 18:14:31 +0100 Alexander Graf ag...@suse.de wrote: Now, if we can get away with not using an undefined instruction (be it sc 64 or trap) I don't know. I'm not even sure we can get away with trap. Basically, WARN_ON should also trigger a trap, so you'd end up in gdb for that when having a breakpoint defined. There'd need to be a way for qemu/gdb to have KVM reflect the exception to the guest if it doesn't have a breakpoint on file for that address. Yes, but that piece is missing for every KVM target right now. I'd like to see something generic emerge here that we can reuse across different architectures :). Trap seems very tricky too though. According to page 1082 of the 2.06 spec, trap can issue a debug or a program interrupt depending on MSR_DE. I don't see any mentioning in the spec that we intercept program or debug interrupts. So I guess we'd have to override the offset vectors and handle _every_ interrupt ourselves. Bleks. Alex -- To unsubscribe from this list: send the line unsubscribe kvm-ppc in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: Software breakpoint in kvmppc guest debug
On Tue, 9 Nov 2010 19:26:25 +0100 Alexander Graf ag...@suse.de wrote: On 09.11.2010, at 19:17, Scott Wood wrote: On Tue, 9 Nov 2010 18:14:31 +0100 Alexander Graf ag...@suse.de wrote: Now, if we can get away with not using an undefined instruction (be it sc 64 or trap) I don't know. I'm not even sure we can get away with trap. Basically, WARN_ON should also trigger a trap, so you'd end up in gdb for that when having a breakpoint defined. There'd need to be a way for qemu/gdb to have KVM reflect the exception to the guest if it doesn't have a breakpoint on file for that address. Yes, but that piece is missing for every KVM target right now. I'd like to see something generic emerge here that we can reuse across different architectures :). We should try to define something that will make sense on other architectures, to whatever extent is practical -- but that doesn't mean we need to wait for them to act first. :-) Trap seems very tricky too though. According to page 1082 of the 2.06 spec, trap can issue a debug or a program interrupt depending on MSR_DE. I don't see any mentioning in the spec that we intercept program or debug interrupts. So I guess we'd have to override the offset vectors and handle _every_ interrupt ourselves. Bleks. Program and debug interrupts always go to the hypervisor. Only the exceptions for which GIVORs are defined (DSI, ISI, external IRQ, syscall, TLB miss) can go directly to the guest, and even those are generally optional based on EPCR. -Scott -- To unsubscribe from this list: send the line unsubscribe kvm-ppc in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: Software breakpoint in kvmppc guest debug
On 09.11.2010, at 19:43, Scott Wood wrote: On Tue, 9 Nov 2010 19:26:25 +0100 Alexander Graf ag...@suse.de wrote: On 09.11.2010, at 19:17, Scott Wood wrote: On Tue, 9 Nov 2010 18:14:31 +0100 Alexander Graf ag...@suse.de wrote: Now, if we can get away with not using an undefined instruction (be it sc 64 or trap) I don't know. I'm not even sure we can get away with trap. Basically, WARN_ON should also trigger a trap, so you'd end up in gdb for that when having a breakpoint defined. There'd need to be a way for qemu/gdb to have KVM reflect the exception to the guest if it doesn't have a breakpoint on file for that address. Yes, but that piece is missing for every KVM target right now. I'd like to see something generic emerge here that we can reuse across different architectures :). We should try to define something that will make sense on other architectures, to whatever extent is practical -- but that doesn't mean we need to wait for them to act first. :-) Oh, I agree. I'm saying we should have Jan in the discussion :). Trap seems very tricky too though. According to page 1082 of the 2.06 spec, trap can issue a debug or a program interrupt depending on MSR_DE. I don't see any mentioning in the spec that we intercept program or debug interrupts. So I guess we'd have to override the offset vectors and handle _every_ interrupt ourselves. Bleks. Program and debug interrupts always go to the hypervisor. Only the exceptions for which GIVORs are defined (DSI, ISI, external IRQ, syscall, TLB miss) can go directly to the guest, and even those are generally optional based on EPCR. Ah, so it's a positive list. I guess I missed that part :). Thanks for the clarification. So making it a trap instruction for now should be ok. Let's align the code to the same x86 looks like for now. In the meanwhile, let's discuss with Jan on how to get a list of patched IPs into the kernel and implement that on top of the code we'll have aligned with x86 by then :). Alex -- To unsubscribe from this list: send the line unsubscribe kvm-ppc in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
RE: Software breakpoint in kvmppc guest debug
-Original Message- From: kvm-ppc-ow...@vger.kernel.org [mailto:kvm-ppc-ow...@vger.kernel.org] On Behalf Of Alexander Graf Sent: Tuesday, November 09, 2010 12:50 PM To: Wood Scott-B07421 Cc: Hollis Blanchard; Liu Yu-B13201; kvm-ppc@vger.kernel.org; Jan Kiszka Subject: Re: Software breakpoint in kvmppc guest debug On 09.11.2010, at 19:43, Scott Wood wrote: On Tue, 9 Nov 2010 19:26:25 +0100 Alexander Graf ag...@suse.de wrote: On 09.11.2010, at 19:17, Scott Wood wrote: On Tue, 9 Nov 2010 18:14:31 +0100 Alexander Graf ag...@suse.de wrote: Now, if we can get away with not using an undefined instruction (be it sc 64 or trap) I don't know. I'm not even sure we can get away with trap. Basically, WARN_ON should also trigger a trap, so you'd end up in gdb for that when having a breakpoint defined. There'd need to be a way for qemu/gdb to have KVM reflect the exception to the guest if it doesn't have a breakpoint on file for that address. Yes, but that piece is missing for every KVM target right now. I'd like to see something generic emerge here that we can reuse across different architectures :). We should try to define something that will make sense on other architectures, to whatever extent is practical -- but that doesn't mean we need to wait for them to act first. :-) Oh, I agree. I'm saying we should have Jan in the discussion :). Trap seems very tricky too though. According to page 1082 of the 2.06 spec, trap can issue a debug or a program interrupt depending on MSR_DE. I don't see any mentioning in the spec that we intercept program or debug interrupts. So I guess we'd have to override the offset vectors and handle _every_ interrupt ourselves. Bleks. Program and debug interrupts always go to the hypervisor. Only the exceptions for which GIVORs are defined (DSI, ISI, external IRQ, syscall, TLB miss) can go directly to the guest, and even those are generally optional based on EPCR. Ah, so it's a positive list. I guess I missed that part :). Thanks for the clarification. So making it a trap instruction for now should be ok. Let's align the code to the same x86 looks like for now. In the meanwhile, let's discuss with Jan on how to get a list of patched IPs into the kernel and implement that on top of the code we'll have aligned with x86 by then :). What about using the ehpriv instruction (defined in 2.06)? We could define a unique qemu software breakpoint, and the hypervisor's ehpriv handler will be able to easily distinguish them. On e500v2, this would be an illegal instruction. We don't need to worry about a conflict with future opcodes and it seems like the whole point of ehpriv being defined-- to let a hypervisor define special opcodes for stuff like this. If we use trap, we will need the list of patched IPs in the kernel. ehpriv avoids the need for that. Stuart -- To unsubscribe from this list: send the line unsubscribe kvm-ppc in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: Software breakpoint in kvmppc guest debug
On 10.11.2010, at 04:31, Yoder Stuart-B08248 wrote: -Original Message- From: kvm-ppc-ow...@vger.kernel.org [mailto:kvm-ppc-ow...@vger.kernel.org] On Behalf Of Alexander Graf Sent: Tuesday, November 09, 2010 12:50 PM To: Wood Scott-B07421 Cc: Hollis Blanchard; Liu Yu-B13201; kvm-ppc@vger.kernel.org; Jan Kiszka Subject: Re: Software breakpoint in kvmppc guest debug On 09.11.2010, at 19:43, Scott Wood wrote: On Tue, 9 Nov 2010 19:26:25 +0100 Alexander Graf ag...@suse.de wrote: On 09.11.2010, at 19:17, Scott Wood wrote: On Tue, 9 Nov 2010 18:14:31 +0100 Alexander Graf ag...@suse.de wrote: Now, if we can get away with not using an undefined instruction (be it sc 64 or trap) I don't know. I'm not even sure we can get away with trap. Basically, WARN_ON should also trigger a trap, so you'd end up in gdb for that when having a breakpoint defined. There'd need to be a way for qemu/gdb to have KVM reflect the exception to the guest if it doesn't have a breakpoint on file for that address. Yes, but that piece is missing for every KVM target right now. I'd like to see something generic emerge here that we can reuse across different architectures :). We should try to define something that will make sense on other architectures, to whatever extent is practical -- but that doesn't mean we need to wait for them to act first. :-) Oh, I agree. I'm saying we should have Jan in the discussion :). Trap seems very tricky too though. According to page 1082 of the 2.06 spec, trap can issue a debug or a program interrupt depending on MSR_DE. I don't see any mentioning in the spec that we intercept program or debug interrupts. So I guess we'd have to override the offset vectors and handle _every_ interrupt ourselves. Bleks. Program and debug interrupts always go to the hypervisor. Only the exceptions for which GIVORs are defined (DSI, ISI, external IRQ, syscall, TLB miss) can go directly to the guest, and even those are generally optional based on EPCR. Ah, so it's a positive list. I guess I missed that part :). Thanks for the clarification. So making it a trap instruction for now should be ok. Let's align the code to the same x86 looks like for now. In the meanwhile, let's discuss with Jan on how to get a list of patched IPs into the kernel and implement that on top of the code we'll have aligned with x86 by then :). What about using the ehpriv instruction (defined in 2.06)? We could define a unique qemu software breakpoint, and the hypervisor's ehpriv handler will be able to easily distinguish them. On e500v2, this would be an illegal instruction. We don't need to worry about a conflict with future opcodes and it seems like the whole point of ehpriv being defined-- to let a hypervisor define special opcodes for stuff like this. Yes, it even states so in the little box below the description. Very good catch! If we use trap, we will need the list of patched IPs in the kernel. ehpriv avoids the need for that. Well, the way it's handled on x86 now is that the kernel asks user space if it knows about the breakpoint and if not user space reinjects the debug interrupt into the guest. Is there anything that ensures us BookS won't use 31/270? Alex -- To unsubscribe from this list: send the line unsubscribe kvm-ppc in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Software breakpoint in kvmppc guest debug
Hello all, Software breakpoint is a instruction which should make guest exit. We replace guest code with software breakpoint instruction so that we can stop at anywhere we want. In my previous guest debug patches for e500, I used instruction (sc 64) as software breakpoint. Seem this was not good, since (sc 64) maybe defined in future. also this instruction has uncertain effective on E.HV platform such as e500mc. Another choice is to use trap instruction. In order to distinguish between real guest trap and software breakpoint trap. It's needed to trace software breakpoint addressed in kernel, and we need to create ioctls to add/remove software point. So guys, which way should we choose? Or is there any other better idea? Thanks, Yu
