linux-kernel - Re: [Xen-devel] [PATCH 2/2] x86/xen: dont add memory above max allowed allocation

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Date:   Tue, 22 Jan 2019 01:52:32 -0700
From:   "Jan Beulich" <JBeulich@...e.com>
To:     "Juergen Gross" <jgross@...e.com>
Cc:     "Borislav Petkov" <bp@...en8.de>,
        "Stefano Stabellini" <sstabellini@...nel.org>,
        "the arch/x86 maintainers" <x86@...nel.org>, <linux-mm@...ck.org>,
        <tglx@...utronix.de>, "xen-devel" <xen-devel@...ts.xenproject.org>,
        "Boris Ostrovsky" <boris.ostrovsky@...cle.com>, <mingo@...hat.com>,
        <linux-kernel@...r.kernel.org>, <hpa@...or.com>
Subject: Re: [Xen-devel] [PATCH 2/2] x86/xen: dont add memory above max
 allowed allocation

>>> On 22.01.19 at 09:06, <jgross@...e.com> wrote:
> Don't allow memory to be added above the allowed maximum allocation
> limit set by Xen.

This reads as if the hypervisor was imposing a limit here, but looking at
xen_get_max_pages(), xen_foreach_remap_area(), and
xen_count_remap_pages() I take it that it's a restriction enforced by
the Xen subsystem in Linux. Furthermore from the cover letter I imply
that the observed issue was on a Dom0, yet xen_get_max_pages()'s
use of XENMEM_maximum_reservation wouldn't impose any limit there
at all (without use of the hypervisor option "dom0_mem=max:..."),
would it?

Jan