Re: [Xen-devel] [PATCH v10 00/16] improve late microcode loading

From: Chao Gao <chao.gao@intel.com>
To: Jan Beulich <jbeulich@suse.com>
Cc: "Sergey Dyasli" <sergey.dyasli@citrix.com>,
	"Ashok Raj" <ashok.raj@intel.com>, "Wei Liu" <wl@xen.org>,
	"Andrew Cooper" <andrew.cooper3@citrix.com>,
	"Suravee Suthikulpanit" <suravee.suthikulpanit@amd.com>,
	xen-devel@lists.xenproject.org,
	"Boris Ostrovsky" <boris.ostrovsky@oracle.com>,
	"Roger Pau Monné" <roger.pau@citrix.com>
Subject: Re: [Xen-devel] [PATCH v10 00/16] improve late microcode loading
Date: Tue, 17 Sep 2019 15:09:23 +0800	[thread overview]
Message-ID: <20190917070922.GA10190@gao-cwp> (raw)
In-Reply-To: <3f3ef22a-0a56-ac77-3deb-513031c8baaa@suse.com>

On Fri, Sep 13, 2019 at 10:47:36AM +0200, Jan Beulich wrote:
>On 12.09.2019 09:22, Chao Gao wrote:
>> This series includes below changes:
>>  1. Patch 1-11: introduce a global microcode cache and some cleanup
>>  2. Patch 12: synchronize late microcode loading
>>  3. Patch 13: support parallel microcodes update on different cores
>>  4. Patch 14: block #NMI handling during microcode loading
>>  5. Patch 15: disable late ucode loading due to BDF90
>>  6. Patch 16: call wbinvd() conditionally
>
>I don't know why it didn't occur to me earlier, but what about
>parked / offlined CPUs? They'll have their ucode updated when they
>get brought back online, but until then their ucode will disagree
>with that of the online CPUs. For truly offline CPUs this may be
>fine, but parked ones should probably be updated, perhaps via the
>same approach as used when C-state data becomes available (see
>set_cx_pminfo())?

Yes. It provides a means to wake up the parked CPU and a chance to run
some code (like loading ucode). But parked CPUs are cleared from
sibling info and cpu_online_map (see __cpu_disable()). If parallel
ucode loading is expected on parked CPUs, we should be able to
determine the primary threads and the number of cores no matter it is
online or parked. To this end, a new sibling map should be maintained
for each CPU and this map isn't changed when a CPU gets parked.

In Linux kernel, the approach is quite simple: late loading is
prohibited if any CPU is parked; admin should online all parked CPU
before loading ucode.

Do you have any preference?

Thanks
Chao

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