From: David Woodhouse <dwmw2@infradead.org>
To: Andrew Cooper <andrew.cooper3@citrix.com>,
Xen-devel <xen-devel@lists.xen.org>
Cc: Matt Wilson <msw@amazon.com>
Subject: Re: [PATCH v8 15/17] x86/ctxt: Issue a speculation barrier between vcpu contexts
Date: Mon, 15 Jan 2018 22:39:32 +0100 [thread overview]
Message-ID: <1516052372.4937.26.camel@infradead.org> (raw)
In-Reply-To: <1516022599.22147.167.camel@infradead.org>
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On Mon, 2018-01-15 at 14:23 +0100, David Woodhouse wrote:
>
> > >
> > > Also... if you're doing that in context_switch() does it do the right
> > > thing with idle? If a CPU switches to the idle domain and then back
> > > again to the same vCPU, does that do the IBPB twice?
> >
> > Context switches to idle will skip the IBPB because it isn't needed, but
> > any switch to non-idle need it. In your example, we should execute just
> > a single IBPB.
>
> In my example I think we should not execute IBPB at all. We come from a
> given VMCS, sleep for a while, and go back to it. No need for any
> flushing whatsoever.
msw points out that in my example we *don't* execute IBPB at all, I
think.
In both switching to idle, and back to the vCPU, we should hit this
case and not the 'else' case that does the IBPB:
1710 if ( (per_cpu(curr_vcpu, cpu) == next) ||
1711 (is_idle_domain(nextd) && cpu_online(cpu)) )
1712 {
1713 local_irq_enable();
1714 }
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next prev parent reply other threads:[~2018-01-15 21:39 UTC|newest]
Thread overview: 55+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-01-12 18:00 [PATCH v8 00/17] x86: Mitigations for SP2/CVE-2017-5715/Branch Target Injection Andrew Cooper
2018-01-12 18:00 ` [PATCH v8 01/17] x86: Support compiling with indirect branch thunks Andrew Cooper
2018-01-14 19:48 ` David Woodhouse
2018-01-15 0:00 ` Andrew Cooper
2018-01-15 4:11 ` Konrad Rzeszutek Wilk
2018-01-15 10:14 ` Jan Beulich
2018-01-15 10:40 ` Andrew Cooper
2018-01-15 10:48 ` Jan Beulich
2018-01-12 18:00 ` [PATCH v8 02/17] x86: Support indirect thunks from assembly code Andrew Cooper
2018-01-15 10:28 ` Jan Beulich
2018-01-16 13:55 ` Andrew Cooper
2018-01-16 14:00 ` Jan Beulich
2018-02-04 10:57 ` David Woodhouse
2018-02-05 8:56 ` Jan Beulich
2018-01-12 18:00 ` [PATCH v8 03/17] x86/boot: Report details of speculative mitigations Andrew Cooper
2018-01-12 18:00 ` [PATCH v8 04/17] x86/amd: Try to set lfence as being Dispatch Serialising Andrew Cooper
2018-01-12 18:00 ` [PATCH v8 05/17] x86: Introduce alternative indirect thunks Andrew Cooper
2018-01-15 10:53 ` Jan Beulich
2018-01-12 18:00 ` [PATCH v8 06/17] x86/feature: Definitions for Indirect Branch Controls Andrew Cooper
2018-01-12 18:00 ` [PATCH v8 07/17] x86/cmdline: Introduce a command line option to disable IBRS/IBPB, STIBP and IBPB Andrew Cooper
2018-01-12 18:00 ` [PATCH v8 08/17] x86/msr: Emulation of MSR_{SPEC_CTRL, PRED_CMD} for guests Andrew Cooper
2018-01-16 11:10 ` David Woodhouse
2018-01-16 16:58 ` Andrew Cooper
2018-01-17 9:11 ` Jan Beulich
2018-01-17 9:39 ` Andrew Cooper
2018-01-12 18:00 ` [PATCH v8 09/17] x86/migrate: Move MSR_SPEC_CTRL on migrate Andrew Cooper
2018-01-12 18:01 ` [PATCH v8 10/17] x86/hvm: Permit guests direct access to MSR_{SPEC_CTRL, PRED_CMD} Andrew Cooper
2018-01-15 11:11 ` Jan Beulich
2018-01-15 16:02 ` Boris Ostrovsky
2018-01-16 0:39 ` Tian, Kevin
2018-01-12 18:01 ` [PATCH v8 11/17] x86: Protect unaware domains from meddling hyperthreads Andrew Cooper
2018-01-15 11:26 ` Jan Beulich
2018-01-16 21:11 ` Andrew Cooper
2018-01-17 8:40 ` Jan Beulich
2018-01-17 8:43 ` Andrew Cooper
2018-01-12 18:01 ` [PATCH v8 12/17] x86/entry: Organise the use of MSR_SPEC_CTRL at each entry/exit point Andrew Cooper
2018-01-15 12:09 ` Jan Beulich
2018-01-16 21:24 ` Andrew Cooper
2018-01-17 8:47 ` Jan Beulich
2018-01-17 9:25 ` Andrew Cooper
2018-01-12 18:01 ` [PATCH v8 13/17] x86/boot: Calculate the most appropriate BTI mitigation to use Andrew Cooper
2018-01-16 14:10 ` Boris Ostrovsky
2018-01-16 14:13 ` Andrew Cooper
2018-01-16 14:25 ` Boris Ostrovsky
2018-01-16 15:12 ` Andrew Cooper
2018-01-12 18:01 ` [PATCH v8 14/17] x86/entry: Clobber the Return Stack Buffer/Return Address Stack on entry to Xen Andrew Cooper
2018-01-12 18:01 ` [PATCH v8 15/17] x86/ctxt: Issue a speculation barrier between vcpu contexts Andrew Cooper
2018-01-15 12:54 ` David Woodhouse
2018-01-15 13:02 ` Andrew Cooper
2018-01-15 13:23 ` David Woodhouse
2018-01-15 21:39 ` David Woodhouse [this message]
2018-01-17 17:26 ` David Woodhouse
2018-01-18 9:12 ` David Woodhouse
2018-01-12 18:01 ` [PATCH v8 16/17] x86/cpuid: Offer Indirect Branch Controls to guests Andrew Cooper
2018-01-12 18:01 ` [PATCH v8 17/17] x86/idle: Clear SPEC_CTRL while idle Andrew Cooper
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