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

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 08.02.19 at 10:56, <rcojocaru@xxxxxxxxxxxxxxx> 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).
> 
> While the in-guest scenario continues to pose problems, this
> patch fixes the "external" case.

IOW you're papering over the problem rather than fixing it. Why
does altp2m_active get set to true before actually having set up
everything? Shouldn't it get cleared early, but set late?

Jan



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