Re: [PULL 36/53] memory: Optimize replay of guest mapping

[Peter Xu]

On Tue, Apr 04, 2023 at 09:23:21PM +0100, Peter Maydell wrote:
> On Tue, 4 Apr 2023 at 20:13, Michael S. Tsirkin <mst@redhat.com> wrote:
> >
> > On Tue, Apr 04, 2023 at 07:00:04PM +0100, Peter Maydell wrote:
> > > On Thu, 2 Mar 2023 at 08:26, Michael S. Tsirkin <mst@redhat.com> wrote:
> > > >
> > > > From: Zhenzhong Duan <zhenzhong.duan@intel.com>
> > > >
> > > > On x86, there are two notifiers registered due to vtd-ir memory region
> > > > splitting the whole address space. During replay of the address space
> > > > for each notifier, the whole address space is scanned which is
> > > > unnecessory.
> > > >
> > > > We only need to scan the space belong to notifier montiored space.
> > > >
> > > > Assert when notifier is used to monitor beyond iommu memory region's
> > > > address space.
> > >
> > > Hi. This patch seems to have regressed the mps3-an547 board,
> > > which now asserts on startup:
> > >
> > > $ ./build/x86/qemu-system-arm --machine mps3-an547 -serial stdio
> > > -kernel /tmp/an547-mwe/build/test.elf
> > > qemu-system-arm: ../../softmmu/memory.c:1903:
> > > memory_region_register_iommu_notifier: Assertion `n->end <=
> > > memory_region_size(mr)' failed.
> > > Aborted (core dumped)
> > >
> > > (reported under https://gitlab.com/qemu-project/qemu/-/issues/1488)
> > >
> > > Since this commit says it's just an optimization, for the 8.0
> > > release can we simply revert it without breaking anything?
> 
> > Fine to revert by me.  Zhenzhong Duan  can you pls fix up
> > this regression and repost? Maybe fix typos in commit log
> > when reposting. Thanks!
> 
> Would somebody also like to send the 'revert' patch, please?
> I had that all ready to go, but my git send-email setup
> seems to have mysteriously broken and I don't have time to
> fix it this evening :-(

Attached.

> 
> This is the commit message I wrote:
> 
> 
> Revert "memory: Optimize replay of guest mapping"
> 
> This reverts commit 6da24341866fa940fd7d575788a2319514941c77
> ("memory: Optimize replay of guest mapping").
> 
> This change breaks the mps3-an547 board under TCG (and
> probably other TCG boards using an IOMMU), which now
> assert:
> 
> $ ./build/x86/qemu-system-arm --machine mps3-an547 -serial stdio
> -kernel /tmp/an547-mwe/build/test.elf
> qemu-system-arm: ../../softmmu/memory.c:1903:
> memory_region_register_iommu_notifier: Assertion `n->end <=
> memory_region_size(mr)' failed.
> 
> This is because tcg_register_iommu_notifier() registers
> an IOMMU notifier which covers the entire address space,
> so the assertion added in this commit is not correct.
> 
> For the 8.0 release, just revert this commit as it is
> only an optimization.
> 
> Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
> 
> 
> thanks
> -- PMM
> 

-- 
Peter Xu

0001-Revert-memory-Optimize-replay-of-guest-mapping.patch
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