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

Alex Bennée alex.bennee at linaro.org
Wed May 20 05:33:48 PDT 2015

Will Deacon <will.deacon at arm.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 at linaro.org>
>> Reviewed-by: Christoffer Dall <christoffer.dall at linaro.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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