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References: <20170309130616.51286-1-heiko.carstens@de.ibm.com>
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From: Dan Williams <dan.j.williams@intel.com>
Date: Thu, 9 Mar 2017 14:37:55 -0800
Message-ID: <CAPcyv4gX-7BAZOEvi7UShZD0bo6JV1D7tiU5wQweauG0tx=Luw@mail.gmail.com>
Subject: Re: [PATCH 1/2] mm: add private lock to serialize memory hotplug operations
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To: "Rafael J. Wysocki" <rjw@rjwysocki.net>
Cc: Heiko Carstens <heiko.carstens@de.ibm.com>, Andrew Morton <akpm@linux-foundation.org>, Linux MM <linux-mm@kvack.org>, "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>, linux-s390 <linux-s390@vger.kernel.org>, Michal Hocko <mhocko@suse.com>, Vladimir Davydov <vdavydov.dev@gmail.com>, Ben Hutchings <ben@decadent.org.uk>, Gerald Schaefer <gerald.schaefer@de.ibm.com>, Martin Schwidefsky <schwidefsky@de.ibm.com>, Sebastian Ott <sebott@linux.vnet.ibm.com>

On Thu, Mar 9, 2017 at 2:22 PM, Rafael J. Wysocki <rjw@rjwysocki.net> wrote:
> On Thursday, March 09, 2017 11:15:47 PM Rafael J. Wysocki wrote:
>> On Thursday, March 09, 2017 10:10:31 AM Dan Williams wrote:
>> > On Thu, Mar 9, 2017 at 5:39 AM, Rafael J. Wysocki <rjw@rjwysocki.net> wrote:
[..]
>> > I *think* we're ok in this case because unplugging the CPU package
>> > that contains a persistent memory device will trigger
>> > devm_memremap_pages() to call arch_remove_memory(). Removing a pmem
>> > device can't fail. It may be held off while pages are pinned for DMA
>> > memory, but it will eventually complete.
>>
>> What about the offlining, though?  Is it guaranteed that no memory from those
>> ranges will go back online after the acpi_scan_try_to_offline() call in
>> acpi_scan_hot_remove()?
>
> My point is that after the acpi_evaluate_ej0() in acpi_scan_hot_remove() the
> hardware is physically gone, so if anything is still doing DMA to that memory at
> that point, then the user is going to be unhappy.

Hmm, ACPI 6.1 does not have any text about what _EJ0 means for ACPI0012.

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