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From: Henrique de Moraes Holschuh <hmh@hmh.eng.br>
To: "Raj, Ashok" <ashok.raj@intel.com>
Cc: Borislav Petkov <bp@alien8.de>, X86 ML <x86@kernel.org>,
	Arjan Van De Ven <arjan.van.de.ven@intel.com>,
	Tom Lendacky <thomas.lendacky@amd.com>,
	LKML <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 4/7] x86/microcode: Do not upload microcode if CPUs are offline
Date: Wed, 28 Feb 2018 16:07:25 -0300	[thread overview]
Message-ID: <20180228190725.c2yuivmmfiezsict@khazad-dum.debian.net> (raw)
In-Reply-To: <20180228132639.GA23235@araj-mobl1.jf.intel.com>

On Wed, 28 Feb 2018, Raj, Ashok wrote:
> On Wed, Feb 28, 2018 at 10:11:56AM -0300, Henrique de Moraes Holschuh wrote:
> > > Avoid loading microcode if any of the CPUs are offline, and issue a
> > > warning. Having different microcode revisions on the system at any time
> > > is outright dangerous.
> > 
> > Even if we update that microcode during CPU early bring-up, before we
> > mark it on-line and start using it?
> > 
> > AFAIK, late-loading or not, this is what should happen in the current
> > code: APs that are brought up after a microcode update is loaded (either
> > by the early or late driver, it doesn't matter) will be always
> > *early-updated* to the new microcode.
> > 
> > Is it dangerous to have an offline core at an older microcode revision
> > than the online cores?
> 
> We don't want to leave a system and allow the user to update microcode
> when some cpus are offline. Remember cpu_offline in linux is only 
> logical offlining.. so the cpu is still in the system.. it can even 
> participate in MCE for e.g. It is very much alive. Its not a question
> that "Would it not work" but its not worth to leave an open door and 
> being paranoid is best!

I see.  Thanks for the explanation!

> > I am not against the patch, mind you, but I am curious about why it is
> > supposed to be dangerous if we're updating the CPUs before we start
> > using them *anyway*.
> > 
> > Also, if this is really dangerous, does it means safe CPU hotplug isn't
> > possible?  AFAICT, the firmware would have to do it for us, but it
> > *doesn't* have the up-to-date microcode (*we* had to update it)...
> 
> The difference is hot-adding you know you are going to update the current
> microcode. But leaving a cpu in offline state is leaving it stale for a long
> time without realizing that you have some stale cores.

That begs the question: do we have any reasons to not update the
microcode even the offline cores?

-- 
  Henrique Holschuh

  reply	other threads:[~2018-02-28 19:07 UTC|newest]

Thread overview: 26+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-02-28 10:28 [PATCH 0/7] x86/microcode: Improve late loading Borislav Petkov
2018-02-28 10:28 ` [PATCH 1/7] x86/microcode: Get rid of struct apply_microcode_ctx Borislav Petkov
2018-03-08  9:25   ` [tip:x86/pti] " tip-bot for Borislav Petkov
2018-02-28 10:28 ` [PATCH 2/7] x86/microcode/intel: Check microcode revision before updating sibling threads Borislav Petkov
2018-03-08  9:25   ` [tip:x86/pti] " tip-bot for Ashok Raj
2018-02-28 10:28 ` [PATCH 3/7] x86/microcode/intel: Writeback and invalidate caches before updating microcode Borislav Petkov
2018-03-08  9:26   ` [tip:x86/pti] " tip-bot for Ashok Raj
2018-02-28 10:28 ` [PATCH 4/7] x86/microcode: Do not upload microcode if CPUs are offline Borislav Petkov
2018-02-28 13:11   ` Henrique de Moraes Holschuh
2018-02-28 13:26     ` Raj, Ashok
2018-02-28 19:07       ` Henrique de Moraes Holschuh [this message]
2018-03-05 22:06   ` Tom Lendacky
2018-03-08  9:26   ` [tip:x86/pti] " tip-bot for Ashok Raj
2018-02-28 10:28 ` [PATCH 5/7] x86/microcode/intel: Look into the patch cache first Borislav Petkov
2018-03-08  9:27   ` [tip:x86/pti] " tip-bot for Borislav Petkov
2018-02-28 10:28 ` [PATCH 6/7] x86/microcode: Request microcode on the BSP Borislav Petkov
2018-03-05 22:08   ` Tom Lendacky
2018-03-08  9:27   ` [tip:x86/pti] " tip-bot for Borislav Petkov
2018-02-28 10:28 ` [PATCH 7/7] x86/microcode: Synchronize late microcode loading Borislav Petkov
2018-02-28 13:59   ` Henrique de Moraes Holschuh
2018-02-28 14:08     ` Borislav Petkov
2018-02-28 17:48       ` Henrique de Moraes Holschuh
2018-03-05 22:09   ` Tom Lendacky
2018-03-08  9:28   ` [tip:x86/pti] " tip-bot for Ashok Raj
2018-03-05 22:12 ` [PATCH 0/7] x86/microcode: Improve late loading Tom Lendacky
2018-03-05 23:51   ` Raj, Ashok

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