linux-kernel - Re: [PATCH v4 06/12] KVM: arm64: guest debug, add SW break point support

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Message-ID: <87bnhfig2b.fsf@linaro.org>
Date:	Wed, 20 May 2015 13:33:48 +0100
From:	Alex Bennée <alex.bennee@...aro.org>
To:	Will Deacon <will.deacon@....com>
Cc:	"kvm\@vger.kernel.org" <kvm@...r.kernel.org>,
	"linux-arm-kernel\@lists.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"kvmarm\@lists.cs.columbia.edu" <kvmarm@...ts.cs.columbia.edu>,
	"christoffer.dall\@linaro.org" <christoffer.dall@...aro.org>,
	Marc Zyngier <Marc.Zyngier@....com>,
	"peter.maydell\@linaro.org" <peter.maydell@...aro.org>,
	"agraf\@suse.de" <agraf@...e.de>,
	"drjones\@redhat.com" <drjones@...hat.com>,
	"pbonzini\@redhat.com" <pbonzini@...hat.com>,
	"zhichao.huang\@linaro.org" <zhichao.huang@...aro.org>,
	"jan.kiszka\@siemens.com" <jan.kiszka@...mens.com>,
	"dahi\@linux.vnet.ibm.com" <dahi@...ux.vnet.ibm.com>,
	"r65777\@freescale.com" <r65777@...escale.com>,
	"bp\@suse.de" <bp@...e.de>, Gleb Natapov <gleb@...nel.org>,
	Jonathan Corbet <corbet@....net>,
	Russell King <linux@....linux.org.uk>,
	Catalin Marinas <Catalin.Marinas@....com>,
	"open list\:DOCUMENTATION" <linux-doc@...r.kernel.org>,
	open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v4 06/12] KVM: arm64: guest debug, add SW break point support


Will Deacon <will.deacon@....com> writes:

> Hi Alex,
>
> On Fri, May 15, 2015 at 03:27:09PM +0100, Alex Bennée wrote:
>> This adds support for SW breakpoints inserted by userspace.
>> 
>> We do this by trapping all guest software debug exceptions to the
>> hypervisor (MDCR_EL2.TDE). The exit handler sets an exit reason of
>> KVM_EXIT_DEBUG with the kvm_debug_exit_arch structure holding the
>> exception syndrome information.
>> 
>> It will be up to userspace to extract the PC (via GET_ONE_REG) and
>> determine if the debug event was for a breakpoint it inserted. If not
>> userspace will need to re-inject the correct exception restart the
>> hypervisor to deliver the debug exception to the guest.
>> 
>> Any other guest software debug exception (e.g. single step or HW
>> assisted breakpoints) will cause an error and the VM to be killed. This
>> is addressed by later patches which add support for the other debug
>> types.
>> 
>> Signed-off-by: Alex Bennée <alex.bennee@...aro.org>
>> Reviewed-by: Christoffer Dall <christoffer.dall@...aro.org>
>> 
>> ---
>> v2
>>   - update to use new exit struct
>>   - tweak for C setup
>>   - do our setup in debug_setup/clear code
>>   - fixed up comments
>> v3:
>>   - fix spacing in KVM_GUESTDBG_VALID_MASK
>>   - fix and clarify wording on kvm_handle_guest_debug
>>   - handle error case in kvm_handle_guest_debug
>>   - re-word the commit message
>> v4
>>   - rm else leg
>>   - add r-b-tag
>> 
>> diff --git a/Documentation/virtual/kvm/api.txt b/Documentation/virtual/kvm/api.txt
>> index ba635c7..33c8143 100644
>> --- a/Documentation/virtual/kvm/api.txt
>> +++ b/Documentation/virtual/kvm/api.txt
>
> Not sure why, but your patches seem to drop the diffstat which makes it
> slightly more onerous for reviewers trying to figure out which bits touch
> their trees. Are you removing it manually?

No - I'm running:

git pps -v 4 origin/master..HEAD -o guestdbg.patches

Where pps is an alias:

pps = format-patch --cover-letter --summary

Manually expanding the alias gives the same results. I'll have a dig to
see what's going on.

>
> Will

-- 
Alex Bennée
--
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