Peter Maydell <peter.maydell@xxxxxxxxxx> writes: > On 27 April 2015 at 21:04, Christoffer Dall <christoffer.dall@xxxxxxxxxx> wrote: >> On Thu, Apr 23, 2015 at 03:26:53PM +0100, Alex Bennée wrote: >>> >>> Christoffer Dall <christoffer.dall@xxxxxxxxxx> writes: >>> >>> > On Tue, Mar 31, 2015 at 04:08:04PM +0100, Alex Bennée wrote: >>> >> + * just need to report the PC and the HSR values to userspace. >>> >> + * Userspace may decide to re-inject the exception and deliver it to >>> >> + * the guest if it wasn't for the host to deal with. >>> > >>> > now I'm confused - does userspace setup the guest to receive an >>> > exception or does it tell KVM to emulate an exception for the guest or >>> > do we execute the breakpoint without trapping the debug exception? >>> >>> I've made it all go through userspace as we may have to translate the >>> hypervisor visible exception code to what the guest was expecting to see. >>> >> >> ok, so I think you should re-phrase something like: >> >> "Userspace may decide that this exception is caused by the guest using >> debugging itself, and may in that case emulate the guest debug exception >> in userspace before resuming KVM." >> >> But does that really work? Given that we don't support KVM-TCG >> migration, this sounds a little strange. Did we test it? > > The QEMU patches have a TODO note at the point where you'd want > to do this... Design-wise you can do the reinjection in the > kernel or in userspace (ppc QEMU does this in userspace, for > instance) because it's pretty much just setting registers to fake > up the exception-entry into EL1. Code-wise QEMU's ARM code isn't > set up to do it right now, but it shouldn't be too difficult to > persuade the TCG exception-entry code to work for this case too. > > Does the kernel already have a conveniently implemented "inject > exception into guest" lump of code? If so it might be less effort > to do it that way round, maybe. So you pointed out we can't just re-inject the exceptions we get as we need to map from things like ESR_ELx_EC_WATCHPT_LOW to ESR_ELx_EC_WATCHPT_CUR before re-injection. Of course if it is as simple as modifying the ESR_EL1 register and returning +ve in the handle_exit path then I can do that but I assumed if any other wrangling needs doing it should be done in userspace. > > -- PMM -- Alex Bennée -- To unsubscribe from this list: send the line "unsubscribe linux-doc" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
