From mboxrd@z Thu Jan  1 00:00:00 1970
From: Christoffer Dall <christoffer.dall@linaro.org>
Subject: Re: [PATCH v2 06/10] KVM: arm64: guest debug, add SW break point
 support
Date: Tue, 28 Apr 2015 14:56:45 +0200
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Cc: Alex =?iso-8859-1?Q?Benn=E9e?= <alex.bennee@linaro.org>,
	kvm-devel <kvm@vger.kernel.org>,
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	Alexander Graf <agraf@suse.de>,
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	Gleb Natapov <gleb@kernel.org>,
	Jonathan Corbet <corbet@lwn.net>,
	Russell King <linux@arm.linux.org.uk>,
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	Will Deacon <will.deacon@arm.com>,
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To: Peter Maydell <peter.maydell@linaro.org>
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On Tue, Apr 28, 2015 at 10:34:12AM +0100, Peter Maydell wrote:
> On 28 April 2015 at 09:42, Alex Benn=E9e <alex.bennee@linaro.org> wro=
te:
> > Peter Maydell <peter.maydell@linaro.org> 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 assu=
med
> > if any other wrangling needs doing it should be done in userspace.
>=20
> 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).
>=20
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 yo=
u
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