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Date: Tue, 27 Oct 2015 08:39:57 +0100
From: Igor Mammedov <imammedo@redhat.com>
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Subject: Re: [Qemu-devel] [PATCH v2] pc: memhp: enforce minimal 128Mb
 alignment for pc-dimm
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To: Andrey Korolyov <andrey@xdel.ru>
Cc: Paolo Bonzini <pbonzini@redhat.com>, "qemu-devel@nongnu.org" <qemu-devel@nongnu.org>, ehabkost@redhat.com, "Michael S. Tsirkin" <mst@redhat.com>

On Mon, 26 Oct 2015 21:42:05 +0300
Andrey Korolyov <andrey@xdel.ru> wrote:

> > How about following comment:
> > /* Linux guests expect 512/64/128Mb alignment for PAE/x32/x64 arch
> >  * respectively. Windows works fine with 2Mb. To make sure that
> >  * memory hotplug would work with above flavors of Linux set
> >  * minimal alignment to 512Mb (i.e. PAE arch).
> >  * Enforcing minimal alignment bigger than that of a backend
> >  * (2Mb for memory-backend-ram) changes GPAs of the 2nd and
> >  * following DIMMs which breaks migration for older machine types,
> >  * so force minimal alignment only since 2.5 machine type and do not
> >  * apply it to older machine types (prior 2.5)
> >  */
> >
> 
> 
> PAE guests are working with 128Mb alignment just fine, at least
> 3.8...3.16 I`ve tried previously, have you seen a counter-example?

Issue is seen only during unplug when DIMM is not aligned to 
SECTION_SIZE_BITS.