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Re: [Qemu-devel] [PATCH v8 1/9] memory: add section range info for IOMMU

From: Peter Xu
Subject: Re: [Qemu-devel] [PATCH v8 1/9] memory: add section range info for IOMMU notifier
Date: Thu, 6 Apr 2017 18:52:55 +0800
User-agent: Mutt/1.5.24 (2015-08-30)

On Thu, Apr 06, 2017 at 12:42:54PM +0200, Auger Eric wrote:
> Hi Peter,
> On 06/04/2017 09:08, Peter Xu wrote:
> > In this patch, IOMMUNotifier.{start|end} are introduced to store section
> > information for a specific notifier. When notification occurs, we not
> > only check the notification type (MAP|UNMAP), but also check whether the
> > notified iova range overlaps with the range of specific IOMMU notifier,
> > and skip those notifiers if not in the listened range.
> > 
> > When removing an region, we need to make sure we removed the correct
> > VFIOGuestIOMMU by checking the IOMMUNotifier.start address as well.
> > 
> > This patch is solving the problem that vfio-pci devices receive
> > duplicated UNMAP notification on x86 platform when vIOMMU is there. The
> > issue is that x86 IOMMU has a (0, 2^64-1) IOMMU region, which is
> > splitted by the (0xfee00000, 0xfeefffff) IRQ region. AFAIK
> > this (splitted IOMMU region) is only happening on x86.
> I think this is likely to happen on other architectures too as "reserved
> regions" are now exported to the user space.

Good to know this.

> > 
> > This patch also helps vhost to leverage the new interface as well, so
> > that vhost won't get duplicated cache flushes. In that sense, it's an
> > slight performance improvement.
> > 
> > Suggested-by: David Gibson <address@hidden>
> > Signed-off-by: Peter Xu <address@hidden>
> Looks good to me.
> Reviewed-by: Eric Auger <address@hidden>


-- peterx

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