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From: "Luck, Tony" <tony.luck@intel.com>
To: speck@linutronix.de
Subject: [MODERATED] Re: [PATCH 2/3] v4 more sampling fun 2
Date: Fri, 27 Mar 2020 10:23:56 -0700	[thread overview]
Message-ID: <20200327172356.GA13816@agluck-desk2.amr.corp.intel.com> (raw)
In-Reply-To: <20200327162041.GA2707@mtg-dev.jf.intel.com>

On Fri, Mar 27, 2020 at 09:20:41AM -0700, speck for mark gross wrote:
> On Wed, Mar 25, 2020 at 10:19:23PM -0500, speck for Josh Poimboeuf wrote:
> > > +static void __init srbds_select_mitigation(void)
> > > +{
> > > +	u64 ia32_cap;
> > > +
> > > +	if (boot_cpu_has(X86_FEATURE_HYPERVISOR)) {
> > > +		srbds_mitigation = SRBDS_HYPERVISOR;
> > > +		return;
> > > +	}
> > 
> > It's confusing that this comes before the X86_BUG_SRBDS check.  Is that
> > on purpose?
> VM vendors on keybase wanted it so.

No. They don't want this. It results in all multi-socket servers
(which are not affected by SRBDS) saying the mitigation status is
unknown.

The preferred order to check is:

1) Am I on the affected list?

2) Am I running under a hypervisor?


Initially Andrew Cooper had asked for the hypervisor check to come
first. But he has since relented.  Below is a comment to explain
why it is practially better to check for prescence on the affected
list *before* checking for hypervisor:

/*
 * This test relies on the CPUID values of vendor, family, model,
 * stepping which might not reflect the real hardware when we are
 * running as a guest. But VMM vendors have asked that we do this
 * before the X86_FEATURE_HYPERVISOR test since this provides better
 * guidance to users in most real situations.
 */

-Tony

  reply	other threads:[~2020-03-27 17:24 UTC|newest]

Thread overview: 17+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-03-18 21:27 [MODERATED] [PATCH 0/3] v4 more sampling fun 0 mark gross
2020-01-16 22:16 ` [MODERATED] [PATCH 2/3] v4 more sampling fun 2 mark gross
2020-01-30 19:12 ` [MODERATED] [PATCH 3/3] v4 more sampling fun 3 mark gross
2020-03-17  0:56 ` [MODERATED] [PATCH 1/3] v4 more sampling fun 1 mark gross
     [not found] ` <5e7296c7.1c69fb81.f9a2f.00ebSMTPIN_ADDED_BROKEN@mx.google.com>
2020-03-19  8:50   ` [MODERATED] " Greg KH
2020-03-19 15:40     ` mark gross
2020-03-19 15:50       ` Luck, Tony
2020-03-19 16:34         ` Greg KH
2020-03-19 18:13     ` Thomas Gleixner
2020-03-26  3:19 ` [MODERATED] Re: [PATCH 2/3] v4 more sampling fun 2 Josh Poimboeuf
2020-03-27 16:20   ` mark gross
2020-03-27 17:23     ` Luck, Tony [this message]
2020-03-27 19:12       ` mark gross
2020-03-27 17:37     ` Josh Poimboeuf
2020-03-27 19:27       ` mark gross
2020-03-26  3:25 ` [MODERATED] Re: [PATCH 3/3] v4 more sampling fun 3 Josh Poimboeuf
2020-03-27 16:28   ` mark gross

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