From mboxrd@z Thu Jan  1 00:00:00 1970
From: Jeremy Fitzhardinge <jeremy@goop.org>
Subject: Re: [PATCH 08/13] xen/pvticketlock: disable interrupts while blocking
Date: Wed, 07 Sep 2011 12:09:15 -0700
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To: Avi Kivity <avi@redhat.com>
Cc: Don Zickus <dzickus@redhat.com>, Peter Zijlstra <peterz@infradead.org>, "H. Peter Anvin" <hpa@zytor.com>, Linus Torvalds <torvalds@linux-foundation.org>, Ingo Molnar <mingo@elte.hu>, the arch/x86 maintainers <x86@kernel.org>, Linux Kernel Mailing List <linux-kernel@vger.kernel.org>, Nick Piggin <npiggin@kernel.dk>, Marcelo Tosatti <mtosatti@redhat.com>, KVM <kvm@vger.kernel.org>, Andi Kleen <andi@firstfloor.org>, Xen Devel <xen-devel@lists.xensource.com>, Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>, Stefano Stabellini <stefano.stabellini@eu.citrix.com>
List-Id: xen-devel@lists.xenproject.org

On 09/07/2011 10:41 AM, Avi Kivity wrote:
>> Hm, I'm interested to know what you're thinking in more detail.  Can you
>> leave an NMI pending before you block in the same way you can with
>> "sti;halt" with normal interrupts?
>
>
> Nope.  But you can do
>
>    if (regs->rip in critical section)
>            regs->rip = after_halt;
>
> and effectively emulate it.  The critical section is something like
>
>     critical_section_start:
>         if (woken_up)
>             goto critical_section_end;
>         hlt
>     critical_section_end:

Hm.  It's a pity you have to deliver an actual interrupt to implement
the kick though.

>>
>> I was thinking you might want to do something with monitor/mwait to
>> implement the blocking/kick ops. (Handwave)
>>
>
> monitor/mwait are incredibly expensive to virtualize since they
> require write-protecting a page, IPIs flying everywhere and flushing
> tlbs, not to mention my lovely hugepages being broken up mercilessly.

Or what about a futex-like hypercall?

    J