[Xen-devel] Ping: [PATCH] VMX: sync CPU state upon vCPU destruction

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 09.11.17 at 15:49, <JBeulich@xxxxxxxx> wrote:
> See the code comment being added for why we need this.
> 
> Reported-by: Igor Druzhinin <igor.druzhinin@xxxxxxxxxx>
> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>

I realize we aren't settled yet on where to put the sync call. The
discussion appears to have stalled, though. Just to recap,
alternatives to the placement below are
- at the top of complete_domain_destroy(), being the specific
  RCU callback exhibiting the problem (others are unlikely to
  touch guest state)
- in rcu_do_batch(), paralleling the similar call from
  do_tasklet_work()

Jan

> --- a/xen/arch/x86/hvm/vmx/vmx.c
> +++ b/xen/arch/x86/hvm/vmx/vmx.c
> @@ -479,7 +479,13 @@ static void vmx_vcpu_destroy(struct vcpu
>       * we should disable PML manually here. Note that vmx_vcpu_destroy is 
> called
>       * prior to vmx_domain_destroy so we need to disable PML for each vcpu
>       * separately here.
> +     *
> +     * Before doing that though, flush all state for the vCPU previously 
> having
> +     * run on the current CPU, so that this flushing of state won't happen 
> from
> +     * the TLB flush IPI handler behind the back of a vmx_vmcs_enter() /
> +     * vmx_vmcs_exit() section.
>       */
> +    sync_local_execstate();
>      vmx_vcpu_disable_pml(v);
>      vmx_destroy_vmcs(v);
>      passive_domain_destroy(v);
> 
> 
> 
> 
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