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SubjectRe: [RFC Patch 0/9] Hardware Breakpoint interfaces
K.Prasad wrote:
>>> Presently I find plenty of set_debugreg() calls from kvm/ which will
>>> modify the registers directly and break the breakpoint register
>>> management brought-in through the patch.
>> If kvm restores the registers, should there be any problem?
> No, it should be fine although I don't understand how the exception
> handler is invoked in KVM without the use of notifier or a hook in
> die_debug (or have they replaced code at a layer much below that?).

kvm debug traps don't work by raising a debug exception; instead, the
guest #VMEXITs into the host. The kernel debug handler will not be invoked.

> Apart from the doubt I've stated above, if they operate by replacing
> the breakpoint register contents before a context switch from KVM to
> other processes, they might in fact help maximise its utilisation.

Yes. As I mentioned, right now we avoid swapping the debug registers if
we aren't going to context switch or exit to userspace, but if you give
us a predicate that tells us whether you are interested in the debug
registers, we can swap them eagerly rather than lazily.

error compiling committee.c: too many arguments to function

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