Re: [PATCH 01/11] Add shared memory hypercall to PV Linux guest.

From: Gleb Natapov
Date: Mon Nov 02 2009 - 02:07:39 EST

On Sun, Nov 01, 2009 at 11:27:15PM -0500, Rik van Riel wrote:
> On 11/01/2009 06:56 AM, Gleb Natapov wrote:
> >Add hypercall that allows guest and host to setup per cpu shared
> >memory.
> While it is pretty obvious that we should implement
> the asynchronous pagefaults for KVM, so a swap-in
> of a page the host swapped out does not stall the
> entire virtual CPU, I believe that adding extra
> data accesses at context switch time may not be
> the best tradeoff.
> It may be better to simply tell the guest what
> address is faulting (or give the guest some other
> random unique number as a token). Then, once the
> host brings that page into memory, we can send a
> signal to the guest with that same token.
> The problem of finding the task(s) associated with
> that token can be left to the guest. A little more
> complexity on the guest side, but probably worth it
> if we can avoid adding cost to the context switch
> path.
This is precisely what this series implements. The function below
is leftover from previous implementation, not used by the rest of the
patch and removed by a later patch. Just a left over from rebase. Sorry
about that. Will be fixed for future submissions.

> >+static void kvm_end_context_switch(struct task_struct *next)
> >+{
> >+ struct kvm_vcpu_pv_shm *pv_shm =
> >+ per_cpu(kvm_vcpu_pv_shm, smp_processor_id());
> >+
> >+ if (!pv_shm)
> >+ return;
> >+
> >+ pv_shm->current_task = (u64)next;
> >+}
> >+
> --
> All rights reversed.

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