From: Jan Beulich <jbeulich@suse.com>
To: Elliott Mitchell <ehem+xen@m5p.com>
Cc: xen-devel@lists.xenproject.org
Subject: Re: HVM/PVH Balloon crash
Date: Tue, 7 Sep 2021 10:03:51 +0200 [thread overview]
Message-ID: <1b3d4cb1-ba61-0f61-5097-9978462a2401@suse.com> (raw)
In-Reply-To: <YTZ+XsnoKNnV4IOz@mattapan.m5p.com>
On 06.09.2021 22:47, Elliott Mitchell wrote:
> On Mon, Sep 06, 2021 at 09:52:17AM +0200, Jan Beulich wrote:
>> On 06.09.2021 00:10, Elliott Mitchell wrote:
>>> I brought this up a while back, but it still appears to be present and
>>> the latest observations appear rather serious.
>>>
>>> I'm unsure of the entire set of conditions for reproduction.
>>>
>>> Domain 0 on this machine is PV (I think the BIOS enables the IOMMU, but
>>> this is an older AMD IOMMU).
>>>
>>> This has been confirmed with Xen 4.11 and Xen 4.14. This includes
>>> Debian's patches, but those are mostly backports or environment
>>> adjustments.
>>>
>>> Domain 0 is presently using a 4.19 kernel.
>>>
>>> The trigger is creating a HVM or PVH domain where memory does not equal
>>> maxmem.
>>
>> I take it you refer to "[PATCH] x86/pod: Do not fragment PoD memory
>> allocations" submitted very early this year? There you said the issue
>> was with a guest's maxmem exceeding host memory size. Here you seem to
>> be talking of PoD in its normal form of use. Personally I uses this
>> all the time (unless enabling PCI pass-through for a guest, for being
>> incompatible). I've not observed any badness as severe as you've
>> described.
>
> I've got very little idea what is occurring as I'm expecting to be doing
> ARM debugging, not x86 debugging.
>
> I was starting to wonder whether this was widespread or not. As such I
> was reporting the factors which might be different in my environment.
>
> The one which sticks out is the computer has an older AMD processor (you
> a 100% Intel shop?).
No, AMD is as relevant to us as is Intel.
> The processor has the AMD NPT feature, but a very
> early/limited IOMMU (according to Linux "AMD IOMMUv2 functionality not
> available").
>
> Xen 4.14 refused to load the Domain 0 kernel as PVH (not enough of an
> IOMMU).
That sounds odd at the first glance - PVH simply requires that there be
an (enabled) IOMMU. Hence the only thing I could imagine is that Xen
doesn't enable the IOMMU in the first place for some reason.
Jan
next prev parent reply other threads:[~2021-09-07 8:04 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-09-05 22:10 HVM/PVH Ballon crash Elliott Mitchell
2021-09-06 7:52 ` Jan Beulich
2021-09-06 20:47 ` HVM/PVH Balloon crash Elliott Mitchell
2021-09-07 8:03 ` Jan Beulich [this message]
2021-09-07 15:03 ` Elliott Mitchell
2021-09-07 15:57 ` Jan Beulich
2021-09-07 21:40 ` Elliott Mitchell
2021-09-15 2:40 ` Elliott Mitchell
2021-09-15 6:05 ` Jan Beulich
2021-09-26 22:53 ` Elliott Mitchell
2021-09-29 13:32 ` Jan Beulich
2021-09-29 15:31 ` Elliott Mitchell
2021-09-30 7:08 ` Jan Beulich
2021-10-02 2:35 ` Elliott Mitchell
2021-10-07 7:20 ` Jan Beulich
2021-09-30 7:43 ` Jan Beulich
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=1b3d4cb1-ba61-0f61-5097-9978462a2401@suse.com \
--to=jbeulich@suse.com \
--cc=ehem+xen@m5p.com \
--cc=xen-devel@lists.xenproject.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.