Re: [Xen-ia64-devel][PATCH][VTD] small patches for VTD

[Isaku Yamahata <yamahata@xxxxxxxxxxxxx>]

Applied, thanks.

On Fri, Oct 24, 2008 at 11:02:21AM +0800, Xu, Anthony wrote:
> Isaku Yamahata wrote:
> > On Thu, Oct 23, 2008 at 03:10:55PM +0800, Xu, Anthony wrote:
> >> The new one,
> > 
> > It looks almost okay. The last one.
> > 
> > 
> >> diff -r 02c8733e2d91 xen/arch/ia64/vmx/viosapic.c
> >> --- a/xen/arch/ia64/vmx/viosapic.c Wed Oct 22 17:20:15 2008 +0900
> >> +++ b/xen/arch/ia64/vmx/viosapic.c Thu Oct 23 14:48:09 2008 +0800 @@
> >>                       -121,6 +121,13 @@ redir_num, vector);
> >>          return;
> >>      }
> >> +    if ( iommu_enabled )
> >> +    {
> >> +        spin_unlock(&viosapic->lock);
> >> +        hvm_dpci_eoi(current->domain, redir_num,
> >> &viosapic->redirtbl[redir_num]); +        spin_lock(&viosapic->lock);
> >> +    }
> >> +
> >>      service_iosapic(viosapic);
> >>      spin_unlock(&viosapic->lock);
> >>  }
> > 
> > Is this unlock/lock sequence okay?
> > I'm asking simply because I'm not sure.
> > 
> > viosapic->irr and isr are protected by the lock.
> > And viosapic_update_EOI() updates them atomically.
> > The above unlock/lock seems to break its atomicity.
> 
> I think it is Okay,
> One atomical operation in viosapic_update_EOI is divided into two atomical 
> operations.
> If you get spin_lock again, when returning from hvm_dpci_eoi.
> There are many code segments in linux kernel.
> And viosapic->irr and isr is still protected by lock.
> 
> Anthony
> 
> > 
> > I'm not sure it's okay or not. To make sure, it is required
> > to take closer look at viosapic.c.
> > 
> > thanks,
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> 

-- 
yamahata

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