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Re: [Xen-devel] [PATCH 6/8] x86: (command line option to) avoid use of secondary hyper-threads


  • To: Jan Beulich <JBeulich@xxxxxxxx>, xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxxx>
  • From: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
  • Date: Thu, 12 Jul 2018 16:45:39 +0100
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  • Cc: George Dunlap <George.Dunlap@xxxxxxxxxxxxx>, Brian Woods <brian.woods@xxxxxxx>, Suravee Suthikulpanit <suravee.suthikulpanit@xxxxxxx>, Dario Faggioli <dfaggioli@xxxxxxxx>
  • Delivery-date: Thu, 12 Jul 2018 16:00:30 +0000
  • List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
  • Openpgp: preference=signencrypt

On 11/07/18 13:10, Jan Beulich wrote:
> Shared resources (L1 cache and TLB in particular) present a risk of
> information leak via side channels. Don't use hyperthreads in such
> cases, but allow independent control of their use at the same time.
>
> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
> ---
> An option to avoid the up/down cycle would be to avoid clearing the
> sibling (and then perhaps also core) map of parked CPUs, allowing to
> bail early from cpu_up_helper().
>
> TBD: How to prevent the CPU from transiently becoming available for
>      scheduling when being onlined at runtime?

This looks like an argument for cancelling at call-in time, no?

> --- a/docs/misc/xen-command-line.markdown
> +++ b/docs/misc/xen-command-line.markdown
> @@ -1040,6 +1040,13 @@ identical to the boot CPU will be parked
>  ### hpetbroadcast (x86)
>  > `= <boolean>`
>  
> +### ht (x86)

I'd suggest smt rather than ht here.  SMT is the technical term, while
HT is Intel's marketing name.

~Andrew

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