From: Juergen Gross <jgross@suse.com>
To: Jan Beulich <JBeulich@suse.com>
Cc: Stefano Stabellini <sstabellini@kernel.org>,
the arch/x86 maintainers <x86@kernel.org>,
linux-kernel@vger.kernel.org, mingo@redhat.com,
Borislav Petkov <bp@alien8.de>,
hpa@zytor.com, xen-devel <xen-devel@lists.xenproject.org>,
Boris Ostrovsky <boris.ostrovsky@oracle.com>,
tglx@linutronix.de
Subject: Re: [Xen-devel] [PATCH] x86/xen: disable nosmt in Xen guests
Date: Wed, 12 Jun 2019 12:36:49 +0200 [thread overview]
Message-ID: <8392fdc4-a6b2-a3aa-dca6-0a0ad7a411be@suse.com> (raw)
In-Reply-To: <5D00D1A602000078002376A9@prv1-mh.provo.novell.com>
On 12.06.19 12:19, Jan Beulich wrote:
>>>> On 12.06.19 at 12:12, <jgross@suse.com> wrote:
>> When running as a Xen guest selecting "nosmt" either via command line
>> or implicitly via default settings makes no sense, as the guest has no
>> clue about the real system topology it is running on. With Xen it is
>> the hypervisor's job to ensure the proper bug mitigations are active
>> regarding smt settings.
>
> I don't agree with the second sentence: It is in principle fine for the
> hypervisor to expose HT (i.e. not disable it as bug mitigation), and
> leave it to the guest kernels to protect themselves. We're just not
> at the point yet where Xen offers sufficient / reliable data to guest
> kernels to do so, so _for the time being_ what you say is correct.
Okay, I'll add something like:
This is true as long Xen doesn't support core scheduling together with
exposing the (then) correct sibling information to the guest and
indicating that case via a sutable interface.
Juergen
_______________________________________________
Xen-devel mailing list
Xen-devel@lists.xenproject.org
https://lists.xenproject.org/mailman/listinfo/xen-devel
next prev parent reply other threads:[~2019-06-12 10:37 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-06-12 10:12 [Xen-devel] [PATCH] x86/xen: disable nosmt in Xen guests Juergen Gross
2019-06-12 10:19 ` Jan Beulich
2019-06-12 10:36 ` Juergen Gross [this message]
2019-06-12 11:48 ` Peter Zijlstra
2019-06-12 14:59 ` Juergen Gross
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=8392fdc4-a6b2-a3aa-dca6-0a0ad7a411be@suse.com \
--to=jgross@suse.com \
--cc=JBeulich@suse.com \
--cc=boris.ostrovsky@oracle.com \
--cc=bp@alien8.de \
--cc=hpa@zytor.com \
--cc=linux-kernel@vger.kernel.org \
--cc=mingo@redhat.com \
--cc=sstabellini@kernel.org \
--cc=tglx@linutronix.de \
--cc=x86@kernel.org \
--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 a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).