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    SubjectRe: [PATCH v3] mm/hotplug: Only respect mem= parameter during boot stage
    On 02/04/20 at 08:53am, Jürgen Groß wrote:
    > On 04.02.20 06:06, Baoquan He wrote:
    > > In commit 357b4da50a62 ("x86: respect memory size limiting via mem=
    > > parameter") a global varialbe max_mem_size is added to store
    > > the value parsed from 'mem= ', then checked when memory region is
    > > added. This truly stops those DIMMs from being added into system memory
    > > during boot-time.
    > >
    > > However, it also limits the later memory hotplug functionality. Any
    > > DIMM can't be hotplugged any more if its region is beyond the
    > > max_mem_size. We will get errors like:
    > >
    > > [ 216.387164] acpi PNP0C80:02: add_memory failed
    > > [ 216.389301] acpi PNP0C80:02: acpi_memory_enable_device() error
    > > [ 216.392187] acpi PNP0C80:02: Enumeration failure
    > >
    > > This will cause issue in a known use case where 'mem=' is added to
    > > the hypervisor. The memory that lies after 'mem=' boundary will be
    > > assigned to KVM guests. After commit 357b4da50a62 merged, memory
    > > can't be extended dynamically if system memory on hypervisor is not
    > > sufficient.
    > >
    > > So fix it by also checking if it's during boot-time restricting to add
    > > memory. Otherwise, skip the restriction.
    > >
    > > And also add this use case to document of 'mem=' kernel parameter.
    > >
    > > Fixes: 357b4da50a62 ("x86: respect memory size limiting via mem= parameter")
    > > Signed-off-by: Baoquan He <bhe@redhat.com>
    >
    > Reviewed-by: Juergen Gross <jgross@suse.com>

    Thanks, Juergen. Seems I should add more details to explain this. Will
    post v4 with your 'Reviewed-by'.

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