From: "Jan Beulich" <JBeulich@suse.com>
To: Andrew Cooper <andrew.cooper3@citrix.com>
Cc: Kevin Tian <kevin.tian@intel.com>,
Ashok Raj <ashok.raj@intel.com>,
xen-devel@lists.xen.org, Jun Nakajima <jun.nakajima@intel.com>,
tglx@linutronix.de, Borislav Petkov <bp@suse.de>,
Chao Gao <chao.gao@intel.com>
Subject: Re: [Patch v3 2/2] x86/microcode: Synchronize late microcode loading
Date: Wed, 16 May 2018 07:46:48 -0600 [thread overview]
Message-ID: <5AFC364802000078001C3436@prv1-mh.provo.novell.com> (raw)
In-Reply-To: <d11a6abe-6ee7-30a5-db07-2fa09f596064@citrix.com>
>>> On 16.05.18 at 15:25, <andrew.cooper3@citrix.com> wrote:
> On 16/05/18 14:10, Jan Beulich wrote:
>>> +static int do_microcode_update(void *_info)
>>> +{
>>> + struct microcode_info *info = _info;
>>> + unsigned int cpu = smp_processor_id();
>>> + int ret;
>>> +
>>> + ret = wait_for_cpus(&info->cpu_in, MICROCODE_DEFAULT_TIMEOUT);
>>> + if ( ret )
>>> + return ret;
>>> +
>>> + /*
>>> + * Logical threads which set the first bit in cpu_sibling_mask can do
>>> + * the update. Other sibling threads just await the completion of
>>> + * microcode update.
>>> + */
>>> + if ( !cpumask_test_and_set_cpu(
>>> + cpumask_first(per_cpu(cpu_sibling_mask, cpu)), &info->cpus) )
>>> + ret = microcode_update_cpu(info->buffer, info->buffer_size);
>>> + /*
>>> + * Increase the wait timeout to a safe value here since we're serializing
>>> + * the microcode update and that could take a while on a large number of
>>> + * CPUs. And that is fine as the *actual* timeout will be determined by
>>> + * the last CPU finished updating and thus cut short
>>> + */
>>> + if ( wait_for_cpus(&info->cpu_out, MICROCODE_DEFAULT_TIMEOUT *
>>> + nr_phys_cpus) )
>> I remain unconvinced that this is a safe thing to do on a huge system with
>> guests running (even Dom0 alone would seem risky enough). I continue to
>> hope for comments from others, in particular Andrew, here. At the very
>> least I think you should taint the hypervisor when making it here.
>
> I see nothing in this patch which prevents a deadlock against the time
> calibration rendezvous. It think its fine to pause the time calibration
> rendezvous while performing this update.
If there's a problem here, wouldn't that be a general one with
stop_machine()?
> Also, what is the purpose of serialising the updates while all pcpus are
> in rendezvous? Surely at that point the best option is to initiate an
> update on all processors which don't have an online sibling thread with
> a lower thread id.
I've suggested that before.
Jan
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next prev parent reply other threads:[~2018-05-16 13:46 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-05-08 22:01 [Patch v3 1/2] x86/smp: count the number of online physical processor in the system Chao Gao
2018-05-08 22:01 ` [Patch v3 2/2] x86/microcode: Synchronize late microcode loading Chao Gao
2018-05-16 13:10 ` Jan Beulich
2018-05-16 13:25 ` Andrew Cooper
2018-05-16 13:46 ` Jan Beulich [this message]
2018-05-18 7:21 ` Chao Gao
2018-05-22 8:59 ` Chao Gao
2018-05-22 9:26 ` Jan Beulich
2018-05-22 20:14 ` Raj, Ashok
2018-11-13 9:08 ` Chao Gao
2018-11-13 9:09 ` Andrew Cooper
2018-05-16 12:54 ` [Patch v3 1/2] x86/smp: count the number of online physical processor in the system Jan Beulich
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