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

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Message-ID: <8872a401-46e1-ae81-e84e-0e70bdde2cce@suse.com>
Date:   Tue, 22 Jan 2019 10:09:05 +0100
From:   Juergen Gross <jgross@...e.com>
To:     Jan Beulich <JBeulich@...e.com>
Cc:     Borislav Petkov <bp@...en8.de>,
        Stefano Stabellini <sstabellini@...nel.org>,
        the arch/x86 maintainers <x86@...nel.org>,
        linux-mm@...ck.org, Thomas Gleixner <tglx@...utronix.de>,
        xen-devel <xen-devel@...ts.xenproject.org>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>, mingo@...hat.com,
        lkml <linux-kernel@...r.kernel.org>,
        "H. Peter Anvin" <hpa@...or.com>
Subject: Re: [Xen-devel] [PATCH 2/2] x86/xen: dont add memory above max
 allowed allocation

On 22/01/2019 09:52, Jan Beulich wrote:
>>>> 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?

Oh yes, you are right, of course!

I need to check the current reservation and adjust the allowed limit
in case of ballooning and/or memory hotplug.

Thanks for noticing that!


Juergen