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From: Andy Smith <andy@strugglers.net>
To: Andrew Cooper <andrew.cooper3@citrix.com>
Cc: xen-devel@lists.xenproject.org
Subject: Re: Sporadic PV guest malloc.c assertion failures and segfaults unless pv-l1tf=false is set
Date: Sun, 25 Nov 2018 16:29:31 +0000	[thread overview]
Message-ID: <20181125162931.GA3695@bitfolk.com> (raw)
In-Reply-To: <af84e4d0-6b28-4ee9-58a6-fbd56be9c868@citrix.com>

Hi Andrew,

On Sun, Nov 25, 2018 at 02:48:48PM +0000, Andrew Cooper wrote:
> Which are your two types of Intel server?

7 of them have Xeon D-1540, 2 of them have Xeon E5-1680v4. I've
seen this issue on guests running on both kinds, and my reproducer
guest was moved from a production D-1540 server to a test E5-1680v4
and still suffered.

My only available test host at the moment is E5-1680v4.

> You say that you only see this with 64bit Debian kernels?

Yes, but this seems quite subtle. I've got one Debian stretch guest
where php-fpm crashes every time, and another Debian stretch guest
(unknown kernel) where a particular perl script has an assertion
failure in malloc.c every time. Apart from that across several
hundred other guests it's only been observed a handful of times in a
week and these times were all on 64-bit Debian jessie and stretch.
So with the limited data this could still be coincidence.

I have one guest administrator with a 64-bit Gentoo guest saying
they might have seen it once because gcc crashed during a
compilation, but I am still waiting for clarification on that one.

> Could you experiment with disabling PCID (`pcid=0` on the xen command
> line) and seeing if that affects the reproducibility.

I am unable to reproduce the problem with pcid=0. staging-4.10,
64-bit Debian PV guest with the kernel revision just before L1TF
fixes (linux-image-4.9.0-7-amd64 4.9.110-3+deb9u2). Xen dmesg does
say shadow paging is in effect.

Cheers,
Andy

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  reply	other threads:[~2018-11-25 16:29 UTC|newest]

Thread overview: 5+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-11-25  6:18 Sporadic PV guest malloc.c assertion failures and segfaults unless pv-l1tf=false is set Andy Smith
2018-11-25  9:14 ` Andy Smith
2018-11-25 14:48   ` Andrew Cooper
2018-11-25 16:29     ` Andy Smith [this message]
2018-11-25 17:14       ` Andrew Cooper

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