Re: [Xen-devel] [PATCH v1 2/2] common/page_alloc: don't idle-scrub before microcode update

[Julien Grall <julien.grall@xxxxxxx>]

Hi,

On 11/27/18 10:00 AM, Sergey Dyasli wrote:
> Some x86 CPUs has errata regarding microcode updates. The most notorious
> is Broadwell's BDX90: "Loading Microcode ... May Result in a System Hang".
> (URL: 
> https://www.intel.com/content/dam/www/public/us/en/documents/specification-updates/xeon-e7-v4-spec-update.pdf)
>
> CPUs are supposed to be idle during initial microcode update. Idle-scrub
> changes this, making a CPU to go scrubbing (memset) right after it was
> brought up. This can get in a way of microcode update for other CPUs,
> which results in a system hang:
>
>      [    0.000000] CPU Vendor: Intel, Family 6 (0x6), Model 71 (0x47), 
> Stepping 1 (raw 00040671)
>      ...
>      [    2.598813] HVM: Hardware Assisted Paging (HAP) detected
>      [    2.600211] HVM: HAP page sizes: 4kB, 2MB, 1GB
>      [    0.000000] microcode: CPU2 updated from revision 0x11 to 0x1e, date = 
> 2018-04-03
>      [    0.000000] microcode: CPU4 updated from revision 0x11 to 0x1e, d€ 
> 
>
> Prevent this situation by disabling idle scrubbing until
> SYS_STATE_smp_booted is reached.
I am not aware of any issue on Arm that requires delaying the idle 
scrubbing. It is actually probably better to avoid delaying it as it may 
take a long time to boot all CPUs on platform with a high number of 
cores (48 cores or upper).
Cheers,

--
Julien Grall

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