From: "Jan Beulich" <JBeulich@suse.com>
To: "Ashok Raj" <ashok.raj@intel.com>
Cc: Sergey Dyasli <sergey.dyasli@citrix.com>, WeiLiu <wl@xen.org>,
Andrew Cooper <andrew.cooper3@citrix.com>,
xen-devel <xen-devel@lists.xenproject.org>,
Roger Pau Monne <roger.pau@citrix.com>,
Chao Gao <chao.gao@intel.com>
Subject: Re: [Xen-devel] [PATCH v7 09/10] microcode: remove microcode_update_lock
Date: Fri, 14 Jun 2019 02:58:41 -0600 [thread overview]
Message-ID: <5D0361C1020000780023836C@prv1-mh.provo.novell.com> (raw)
In-Reply-To: <20190613174708.GA30122@araj-mobl1.jf.intel.com>
>>> On 13.06.19 at 19:47, <ashok.raj@intel.com> wrote:
> On Thu, Jun 13, 2019 at 08:08:46AM -0600, Jan Beulich wrote:
>> >>> On 13.06.19 at 16:05, <chao.gao@intel.com> wrote:
>> > On Wed, Jun 12, 2019 at 01:38:31AM -0600, Jan Beulich wrote:
>> >>>>> On 11.06.19 at 18:04, <ashok.raj@intel.com> wrote:
>> >>> On Tue, Jun 11, 2019 at 08:46:04PM +0800, Chao Gao wrote:
>> >>>> On Wed, Jun 05, 2019 at 08:53:46AM -0600, Jan Beulich wrote:
>> >>>> >
>> >>>> >> @@ -307,8 +303,7 @@ static int apply_microcode(const struct microcode_patch
>
>> >>> *patch)
>> >>>> >>
>> >>>> >> mc_intel = patch->mc_intel;
>> >>>> >>
>> >>>> >> - /* serialize access to the physical write to MSR 0x79 */
>> >>>> >> - spin_lock_irqsave(µcode_update_lock, flags);
>> >>>> >> + BUG_ON(local_irq_is_enabled());
>> >>>> >>
>> >>>> >> /*
>> >>>> >> * Writeback and invalidate caches before updating microcode to avoid
>> >>>> >
>> >>>> >Thinking about it - what happens if we hit an NMI or #MC here?
>> >>>> >watchdog_disable(), a call to which you add in an earlier patch,
>> >>>> >doesn't really suppress the generation of NMIs, it only tells the
>> >>>> >handler not to look at the accumulated statistics.
>> >>>>
>> >>>> I think they should be suppressed. Ashok, could you confirm it?
>> >>>
>> >>> I think the only sources would be the watchdog as you pointed out
>> >>> which we already touch to keep it from expiring. The perf counters
>> >>> i'm not an expert in, but i'll check. When we are in stop_machine() type
>> >>> flow, its not clear if any of those would fire. (I might be wrong, but let
>> >>> me check).
>> >>
>> >>Well, without disarming the watchdog NMI at the LAPIC / IO-APIC,
>> >>how would it _not_ potentially fire?
>> >
>> > We plan not to prevent NMI being fired. Instead, if one thread of a core
>> > is updating microcode, other threads of this core would stop in the
>> > handler of NMI until the update completion. Is this approach acceptable?
>>
>> Well, I have to return the question: It is you who knows what is or
>> is not acceptable while an ucode update is in progress. In particular
>> it obviously matters how much ucode is involved in the delivery of
>> an NMI (and in allowing the handler to get to the point where you'd
>> "stop" it).
>>
>> If the approach you suggest is fine for the NMI case, I'd then wonder
>> if it couldn't also be used for the #MC one.
>
> Architecturally only one #MC can be active in the system. If a new #MC
> condition happens when MCG_STATUS.MCIP is already set, that would cause
> spontaneous
> shutdown.
That's understood.
> If another NMI arrives on the CPU doing the wrmsr, it will be pended
> in the lapic and delivered after the wrmsr returns. wrmsr flow
> can't be interrupted.
Of course.
Neither part of your response is an argument against adding the same
"defense" to the #MC handler, though. While likely #MC will be fatal
to the system anyway, we should try to avoid making things worse
when we can.
Jan
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next prev parent reply other threads:[~2019-06-14 8:59 UTC|newest]
Thread overview: 64+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-05-27 8:31 [PATCH v7 00/10] improve late microcode loading Chao Gao
2019-05-27 8:31 ` [Xen-devel] " Chao Gao
2019-05-27 8:31 ` [PATCH v7 01/10] misc/xen-ucode: Upload a microcode blob to the hypervisor Chao Gao
2019-05-27 8:31 ` [Xen-devel] " Chao Gao
2019-06-04 16:14 ` Andrew Cooper
2019-06-04 16:23 ` Jan Beulich
2019-06-06 2:29 ` Chao Gao
2019-05-27 8:31 ` [PATCH v7 02/10] microcode/intel: extend microcode_update_match() Chao Gao
2019-05-27 8:31 ` [Xen-devel] " Chao Gao
2019-06-04 14:39 ` Jan Beulich
2019-06-05 13:22 ` Roger Pau Monné
2019-06-05 14:16 ` Jan Beulich
2019-06-06 8:26 ` Chao Gao
2019-06-06 9:01 ` Jan Beulich
2019-05-27 8:31 ` [PATCH v7 03/10] microcode: introduce a global cache of ucode patch Chao Gao
2019-05-27 8:31 ` [Xen-devel] " Chao Gao
2019-06-04 15:03 ` Jan Beulich
2019-06-10 5:33 ` Chao Gao
2019-06-11 6:50 ` Jan Beulich
2019-05-27 8:31 ` [PATCH v7 04/10] microcode: remove struct ucode_cpu_info Chao Gao
2019-05-27 8:31 ` [Xen-devel] " Chao Gao
2019-06-04 15:13 ` Jan Beulich
2019-06-10 7:19 ` Chao Gao
2019-05-27 8:31 ` [PATCH v7 05/10] microcode: remove pointless 'cpu' parameter Chao Gao
2019-05-27 8:31 ` [Xen-devel] " Chao Gao
2019-06-04 15:29 ` Jan Beulich
2019-06-10 7:31 ` Chao Gao
2019-05-27 8:31 ` [PATCH v7 06/10] microcode: split out apply_microcode() from cpu_request_microcode() Chao Gao
2019-05-27 8:31 ` [Xen-devel] " Chao Gao
2019-06-05 12:37 ` Jan Beulich
2019-06-11 3:32 ` Chao Gao
2019-06-11 7:08 ` Jan Beulich
2019-06-11 8:53 ` Chao Gao
2019-06-11 9:15 ` Jan Beulich
2019-05-27 8:31 ` [PATCH v7 07/10] microcode/intel: Writeback and invalidate caches before updating microcode Chao Gao
2019-05-27 8:31 ` [Xen-devel] " Chao Gao
2019-06-05 13:20 ` Jan Beulich
2019-05-27 8:31 ` [PATCH v7 08/10] x86/microcode: Synchronize late microcode loading Chao Gao
2019-05-27 8:31 ` [Xen-devel] " Chao Gao
2019-06-05 14:09 ` Jan Beulich
2019-06-11 12:36 ` Chao Gao
2019-06-11 12:58 ` Jan Beulich
2019-06-11 15:47 ` Raj, Ashok
2019-06-05 14:42 ` Roger Pau Monné
2019-05-27 8:31 ` [PATCH v7 09/10] microcode: remove microcode_update_lock Chao Gao
2019-05-27 8:31 ` [Xen-devel] " Chao Gao
2019-06-05 14:52 ` Roger Pau Monné
2019-06-05 15:15 ` Jan Beulich
2019-06-05 14:53 ` Jan Beulich
2019-06-11 12:46 ` Chao Gao
2019-06-11 13:23 ` Jan Beulich
2019-06-11 16:04 ` Raj, Ashok
2019-06-12 7:38 ` Jan Beulich
2019-06-13 14:05 ` Chao Gao
2019-06-13 14:08 ` Jan Beulich
2019-06-13 14:58 ` Chao Gao
2019-06-13 17:47 ` Raj, Ashok
2019-06-14 8:58 ` Jan Beulich [this message]
2019-05-27 8:31 ` [PATCH v7 10/10] x86/microcode: always collect_cpu_info() during boot Chao Gao
2019-05-27 8:31 ` [Xen-devel] " Chao Gao
2019-06-05 14:56 ` Roger Pau Monné
2019-06-11 13:02 ` Chao Gao
2019-06-05 15:05 ` Jan Beulich
2019-06-11 12:58 ` Chao Gao
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