From mboxrd@z Thu Jan 1 00:00:00 1970 From: christoffer.dall@linaro.org (Christoffer Dall) Date: Tue, 28 Apr 2015 14:56:45 +0200 Subject: [PATCH v2 06/10] KVM: arm64: guest debug, add SW break point support In-Reply-To: References: <1427814488-28467-1-git-send-email-alex.bennee@linaro.org> <1427814488-28467-7-git-send-email-alex.bennee@linaro.org> <20150414082558.GS6186@cbox> <87y4li6hua.fsf@linaro.org> <20150427200407.GG23335@cbox> <87wq0wr6dd.fsf@linaro.org> Message-ID: <20150428125645.GA4137@cbox> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org On Tue, Apr 28, 2015 at 10:34:12AM +0100, Peter Maydell wrote: > On 28 April 2015 at 09:42, Alex Benn?e wrote: > > Peter Maydell writes: > >> 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. > > Well, somebody's got to do it, and it's the same amount of work > either way (fiddling with ESR, making sure we direct the guest > to the right exception vector entry point, maybe a few other > things). > We already have code in the kernel to inject data/instruction aborts, but not sure how much benefit there is in re-using that. It's up to you really, but I think the kernel code should be clear about what the intention is so that we don't end up in a situation where: (1) The intended behavior is unclear/vague, and (2) it doesn't actually work in practice so nobody can follow the code. Thanks, -Christoffer