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Re: [Xen-devel] [PATCH for-4.12 V4] x86/altp2m: fix HVMOP_altp2m_set_domain_state race


  • To: Razvan Cojocaru <rcojocaru@xxxxxxxxxxxxxxx>, <xen-devel@xxxxxxxxxxxxxxxxxxxx>
  • From: George Dunlap <george.dunlap@xxxxxxxxxx>
  • Date: Thu, 14 Feb 2019 18:06:10 +0000
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  • Cc: kevin.tian@xxxxxxxxx, wei.liu2@xxxxxxxxxx, jbeulich@xxxxxxxx, george.dunlap@xxxxxxxxxxxxx, andrew.cooper3@xxxxxxxxxx, jun.nakajima@xxxxxxxxx, roger.pau@xxxxxxxxxx
  • Delivery-date: Thu, 14 Feb 2019 18:06:34 +0000
  • List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
  • Openpgp: preference=signencrypt

On 2/12/19 11:42 AM, Razvan Cojocaru wrote:
> HVMOP_altp2m_set_domain_state does not domain_pause(), presumably
> on purpose (as it was originally supposed to cater to a in-guest
> agent, and a domain pausing itself is not a good idea).
> 
> This can lead to domain crashes in the vmx_vmexit_handler() code
> that checks if the guest has the ability to switch EPTP without an
> exit. That code can __vmread() the host p2m's EPT_POINTER
> (before HVMOP_altp2m_set_domain_state "for_each_vcpu()" has a
> chance to run altp2m_vcpu_initialise(), but after
> d->arch.altp2m_active is set).

Sorry, where exactly does the crash happen?

 -George

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