Christian Ehrhardt wrote:
I thought about implementing it with slots_lock, vcpu->request, etc
but it really looks like overkill for s390.
We could make (some of) it common code, so it won't look so bad.
There's value in having all kvm ports do things similarly; though of
course we shouldn't force the solution when it isn't really needed.
vcpu->requests is useful whenever we modify global VM state that
needs to be seen by all vcpus in host mode; see
kvm_reload_remote_mmus().
yeah I read that code after your first hint in that thread, and I
agree that merging some of this into common code might be good.
But in my opinion not now for this bugfix patch (the intention is just
to prevent a user being able to crash the host via vcpu create,set
mem& and vcpu run in that order).
It might be a good point to further streamline this once we use the
same userspace code, but I think it doesn't make sense yet.
Sure, don't mix bugfixes with infrastructure changes, when possible.
At least today we can assume that we only have one memslot.
Therefore a set_memslot with already created vcpu's will still not
interfere with running vcpus (they can't run without memslot and
since we have only one they won't run).
Anyway I the code is prepared to "meet" running vcpus, because it
might be different in future. To prevent the livelock issue I
changed the code using mutex_trylock and in case I can't get the
lock I explicitly let the vcpu exit from guest.
Why not do it unconditionally?
hmm I might have written that misleading - eventually it's a loop
until it got the lock
while !trylock
kick vcpu out of guest
schedule
There is no reason to kick out guests where I got the lock cleanly as
far as I see.
Especially as I expect the vcpus not running in the common case as i
explained above (can't run without memslot + we only have one => no
vcpu will run).
Still livelockable, unless you stop the vcpu from entering the guest
immediately.
That's why vcpu->requests is so powerful. Not only you kick the vcpu
out of guest mode, you force it to synchronize when it tries to enter again.
--
error compiling committee.c: too many arguments to function
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