linux-kernel - Re: [PATCH v3 1/2] memory_hotplug: Add a bounds check to check_hotplug_memory

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Date:   Tue, 24 Sep 2019 13:45:03 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     David Hildenbrand <david@...hat.com>
Cc:     Alastair D'Silva <alastair@...ilva.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Oscar Salvador <osalvador@...e.com>,
        Pavel Tatashin <pasha.tatashin@...een.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Wei Yang <richard.weiyang@...il.com>, Qian Cai <cai@....pw>,
        Jason Gunthorpe <jgg@...pe.ca>,
        Logan Gunthorpe <logang@...tatee.com>,
        Ira Weiny <ira.weiny@...el.com>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 1/2] memory_hotplug: Add a bounds check to
 check_hotplug_memory_range()

On Tue 24-09-19 11:13:31, David Hildenbrand wrote:
> On 24.09.19 11:09, Michal Hocko wrote:
> > On Tue 24-09-19 11:31:05, Alastair D'Silva wrote:
> >> On Mon, 2019-09-23 at 14:25 +0200, Michal Hocko wrote:
[...]
> >>> This will result in a silent failure (unlike misaligned case). Is
> >>> this
> >>> what we want?
> >>
> >> Good point - I guess it comes down to, is there anything we expect an
> >> end user to do about it? I'm not sure there is, in which case the bad
> >> RC, which is reported up every call chain that I can see, should be
> >> sufficient.
> > 
> > It seems like a clear HW/platform bug to me. And that should better be
> > reported loudly to the log to make sure people do complain to their FW
> > friends and have it fixed.
> > 
> 
> I don't agree in virtual environment. On s390x, MAX_PHYSMEM_BITS is
> configurable. For example, if you have paravirtualized memory hotplug
> (e.g., virtio-mem), you could add memory to the system that violates
> this constraint.

What happens if that is the case. Does the machine change the
configuration in runtime or it needs a reboot?

Anyway, seeing this to be the case in the log would help in whatever
action is necessary to deal with the issue, right?
-- 
Michal Hocko
SUSE Labs