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Re: [Xen-devel] Dom0 Failing to Boot with Recent Linux Kernels (Spectre Mitigations)


  • To: Juergen Gross <jgross@xxxxxxxx>, Brian Woods <brian.woods@xxxxxxx>, xen-devel@xxxxxxxxxxxxx
  • From: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>
  • Date: Wed, 20 Jun 2018 10:52:20 -0400
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  • Delivery-date: Wed, 20 Jun 2018 14:52:25 +0000
  • List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
  • Openpgp: preference=signencrypt

On 06/20/2018 10:27 AM, Boris Ostrovsky wrote:
> On 06/20/2018 02:17 AM, Juergen Gross wrote:
>> On 20/06/18 05:31, Boris Ostrovsky wrote:
>>> On 06/19/2018 05:30 PM, Brian Woods wrote:
>>>> I'm currently seeing an issue where when booting from a recent Linux
>>>> kernel without nospec_store_bypass_disable.  There's a NULL pointer
>>>> having to do with a lock.  I put some printks in and it seems that in
>>>> arch/x86/kernel/process.c
>>>> that speculative_store_bypass_ht_init isn't getting called which
>>>> initializes the spin lock.  
>>>
>>> speculative_store_bypass_ht_init() is not called on PV. For BSP it is
>>> called from native_smp_prepare_cpus() and for APs it is called from
>>> start_secondary(), neither of which is in PV code path.
>>>
>>> I think the most logical place to put it is in cpu_init().
>> I don't think so. speculative_store_bypass_ht_init() requires
>> topology_sibling_cpumask to be setup which happens only after the call
>> of cpu_init().
> Right.
>
>> We should add the call to cpu_bringup() in smp_pv.c
> That still leaves cpu0 uninitialized. xen_pv_smp_prepare_cpus() may need
> this call as well if we are to follow barmetal example.

Oh, and I see now that you posted a patch that does just that.

-boris


>
> I also wonder whether this works at all for !SMP.
>
> -boris
>
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