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From: Juan Quintela <quintela@redhat.com>
In-Reply-To: <20170517165810.18164-2-dgilbert@redhat.com> (David Alan
	Gilbert's message of "Wed, 17 May 2017 17:58:09 +0100")
References: <20170517165810.18164-1-dgilbert@redhat.com>
	<20170517165810.18164-2-dgilbert@redhat.com>
Reply-To: quintela@redhat.com
Date: Wed, 17 May 2017 21:27:04 +0200
Message-ID: <87fug3b7xz.fsf@secure.mitica>
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Subject: Re: [Qemu-devel] [PATCH 1/2] migration: Fix non-multiple of page
 size migration
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To: "Dr. David Alan Gilbert (git)" <dgilbert@redhat.com>
Cc: qemu-devel@nongnu.org, peterx@redhat.com, lvivier@redhat.com

"Dr. David Alan Gilbert (git)" <dgilbert@redhat.com> wrote:
> From: "Dr. David Alan Gilbert" <dgilbert@redhat.com>
>
> Unfortunately it's legal to create a VM with a RAM size that's
> not a multiple of the underlying host page or huge page size.
> Recently I'd changed things to always send host sized pages,
> and that breaks if we have say a 1025MB guest on 2MB hugepages.
>
> Unfortunately we can't just make that illegal since it would break
> migration from/to existing oddly configured VMs.
>
> Symptom: qemu-system-x86_64: Illegal RAM offset 40100000
>      as it transmits the fraction of the hugepage after the end
>      of the RAMBlock (may also cause a crash on the source
>      - possibly due to clearing bits after the bitmap)
>
> Reported-by:  Yumei Huang <yuhuang@redhat.com>
> Red Hat bug: https://bugzilla.redhat.com/show_bug.cgi?id=1449037
>
> Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>


Reviewed-by: Juan Quintela <quintela@redhat.com>

We should really require for new machine types that ramblocks be
multiples of the page size.  This is just asking for trouble.