Re: [Xen-devel] [PATCH v6 1/7] VMX: Permanently assign PI hook vmx_pi_switch_to()

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 28.10.16 at 04:37, <feng.wu@xxxxxxxxx> wrote:
> PI hook vmx_pi_switch_to() is needed even when any previously
> assigned device is detached from the domain. Since 'SN' bit is
> also used to control the CPU side PI and we change the state of
> SN bit in these two functions,

There's just one function you've mentioned up to here.

> --- a/xen/arch/x86/hvm/vmx/vmx.c
> +++ b/xen/arch/x86/hvm/vmx/vmx.c
> @@ -221,9 +221,14 @@ void vmx_pi_hooks_deassign(struct domain *d)
>      ASSERT(d->arch.hvm_domain.vmx.vcpu_block);
>  
>      d->arch.hvm_domain.vmx.vcpu_block = NULL;
> -    d->arch.hvm_domain.vmx.pi_switch_from = NULL;
> -    d->arch.hvm_domain.vmx.pi_switch_to = NULL;

And with the commit message as it is right now, it is completely
unclear why the from hook also gets zapped. In fact, with the
description pointing out a problem with just the SN=1 case, I
don't see what you need the from hook for without devices
assigned, as that's where SN gets set (and you want to avoid
that).

>      d->arch.hvm_domain.vmx.pi_do_resume = NULL;
> +    d->arch.hvm_domain.vmx.pi_switch_from = NULL;
> +
> +    /*
> +     * In fact, we can remove 'vmx_pi_switch_to' inside itself if no new 
> device

s/can/could/

> +     * is in the process of getting assigned and "from" hook is NULL. 
> However,
> +     * it is not straightforward to find a clear solution, so just leave it 
> here.
> +     */
>  }
>  
>  static int vmx_domain_initialise(struct domain *d)

Jan

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