Re: [v1][KVM][PATCH 1/1] kvm:ppc:booehv: direct ISI exception to Guest

[tiejun.chen]

On 05/08/2013 05:20 PM, Caraman Mihai Claudiu-B02008 wrote:

-Original Message-
From: kvm-ow...@vger.kernel.org [mailto:kvm-ow...@vger.kernel.org] On
Behalf Of tiejun.chen
Sent: Wednesday, May 08, 2013 4:54 AM
To: Wood Scott-B07421
Cc: ag...@suse.de; kvm-ppc@vger.kernel.org; k...@vger.kernel.org;
linuxppc-...@lists.ozlabs.org
Subject: Re: [v1][KVM][PATCH 1/1] kvm:ppc:booehv: direct ISI exception to
Guest

On 05/08/2013 07:40 AM, Scott Wood wrote:

On 05/07/2013 06:06:30 AM, Tiejun Chen wrote:

We also can direct ISI exception to Guest like DSI.

Signed-off-by: Tiejun Chen tiejun.c...@windriver.com
---
  arch/powerpc/kvm/booke_emulate.c |3 +++
  arch/powerpc/kvm/e500mc.c|3 ++-
  2 files changed, 5 insertions(+), 1 deletion(-)


Are you seeing a real performance improvement from this?  This will

interfere

No. But after we reduce the exit to host, shouldn't this improve
performance?


We lose some flexibility for this so it make sense only if we gain
measurable improvements.


Sounds we have much more works to do.






somewhat with using the VF bit, if we were to ever do so, since VF only

affects

Sorry, what is the VF you said?


VF stands for virtualization fault see MAS8[VF] and we may use it for 
virtualized


I almost forget this point :)


MMIO. The hypervisor should deny execute access on pages marked with VF. 
Accordingly
in this case guest ISI exceptions should be handled by the hypervisor.


Thanks for your information.

Tiejun

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Re: [PATCH] kvm/ppc: interrupt disabling fixes

[Benjamin Herrenschmidt]

On Wed, 2013-05-08 at 19:35 -0500, Scott Wood wrote:

 Sigh, and then there's this:
 
 #ifdef CONFIG_PPC64
  /* lazy EE magic */
  hard_irq_disable();
  if (lazy_irq_pending()) {
  /* Got an interrupt in between, try again */
  local_irq_enable();
  hard_irq_disable();
  kvm_guest_exit();
  continue;
  }
 
  trace_hardirqs_on();
 #endif
 
 Alex, could you be a bit more descriptive than magic please?  Can  
 this chunk of code be removed if we do the other changes being  
 discussed?  Or should we leave this in and drop the pre-enter  
 hard_irq_disable portion of the proposed changes?
 
 Why are you calling trace_hardirqs_on() here and not in  
 kvmppc_lazy_ee_enable()?  Why are you calling kvm_guest_exit() before  
 you've called kvm_guest_enter()?

I think I originated that magic... it more/less mimmics prep_for_idle,
the goal was to hard disable (because we had soft disabled earlier) and
check if anything happened in between... if it did, abort, and try
again, but it's a bit fishy really.

Ben.


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