Hi Christoffer, On 06/06/17 20:59, Christoffer Dall wrote: > On Mon, May 15, 2017 at 06:43:48PM +0100, James Morse wrote: >> Running the event handler behind VHE-KVM's back has some side effects: The >> event handler will blindly use any registers that are shared between the host >> and guest. The two that I think matter are TPIDR_EL1, and the debug state. The >> guest may have set MDSCR_EL1 so debug exceptions must remain masked. The >> guest's TPIDR_EL1 will be used by the event handler if it accesses per-cpu >> variables. This needs fixing. The first part of this series juggles KVMs use >> of TPIDR_EL2 so that we share it with the host on VHE systems. An equivalent >> change for 32bit is on my todo list. (one alternative to this is to have a >> parody world switch in the SDEI event handler, but this would mean special >> casing interrupted guests, and be an ABI link to KVM.) >> >> Causing a synchronous exception from an event handler will cause KVM to >> hyp-panic, but may silently succeed if the event didn't interrupt a guest. >> (I may WARN_ON() if this happens in a later patch). You because of this you > > The last sentence here doesn't make much sense to me. If this interrupts a VHE-guest, KVM's hyp-vectors remain in vbar_el2. If we then take a synchronous exception, KVM will assume this happened during world switch and panic. In contrast if you didn't interrupt a guest, the kernel vectors are in vbar_el2, so the fault will be handled. This 'silently succeed' only occurred to me when writing the cover-letter, (hence its probably worded badly). I plan to catch it by save-restoring the exception registers, and warning if they've changed as this would hyp-panic if you interrupted a guest. > For the rest of the KVM part it looks mostly good to me, besides the > points I raised in the individual patches. Thanks for taking a look! Thanks, James -- To unsubscribe from this list: send the line "unsubscribe devicetree" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
