Re: [Xen-devel] [PATCH v4] VT-d PI: disable VT-d PI when CPU-side PI isn't enabled

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 13.06.17 at 10:20, <chao.gao@xxxxxxxxx> wrote:
> From the context calling pi_desc_init(), we can conclude the current
> implementation of VT-d PI depends on CPU-side PI. If we enable VT-d PI
> and disable CPU-side PI by disabling APICv explicitly in xen boot
> command line, we would get an assertion failure.
> 
> This patch clears iommu_intpost once finding CPU-side PI won't be enabled.
> It is safe for this is done before this flag starts taking effect. Also
> take this chance to remove the useless check of "acknowledge interrupt on
> exit", which is a minimal requirement which has been checked earlier.
> 
> Signed-off-by: Chao Gao <chao.gao@xxxxxxxxx>
> ---
> v4:
> - Remove APICv stuff
> - Remove a useless check of "acknowledge interrupt on exit"
> 
> v3:
> - check relevant bit directly other than checking the apicv option
> - add sample of 'xl dmesg'
> 
> v2:
> - add missing S-o-b
> - comments changes
> - change bool_t to bool and move 'opt_apicv_enabled' declaration to vmcs.h
> 
> ---
>  xen/arch/x86/hvm/vmx/vmcs.c | 16 ++++++++++++----
>  1 file changed, 12 insertions(+), 4 deletions(-)
> 
> diff --git a/xen/arch/x86/hvm/vmx/vmcs.c b/xen/arch/x86/hvm/vmx/vmcs.c
> index 8103b20..58f89df 100644
> --- a/xen/arch/x86/hvm/vmx/vmcs.c
> +++ b/xen/arch/x86/hvm/vmx/vmcs.c
> @@ -345,11 +345,19 @@ static int vmx_init_vmcs_config(void)
>  
>      /*
>       * "Process posted interrupt" can be set only when "virtual-interrupt
> -     * delivery" and "acknowledge interrupt on exit" is set
> +     * delivery" and "acknowledge interrupt on exit" is set. For the latter
> +     * is a minimal requirement, only check the former, which is optional.
>       */
> -    if ( !(_vmx_secondary_exec_control & 
> SECONDARY_EXEC_VIRTUAL_INTR_DELIVERY)
> -          || !(_vmx_vmexit_control & VM_EXIT_ACK_INTR_ON_EXIT) )
> -        _vmx_pin_based_exec_control  &= ~ PIN_BASED_POSTED_INTERRUPT;
> +    if ( !(_vmx_secondary_exec_control & 
> SECONDARY_EXEC_VIRTUAL_INTR_DELIVERY) )
> +        _vmx_pin_based_exec_control &= ~ PIN_BASED_POSTED_INTERRUPT;
> +
> +    if ( iommu_intpost
> +          && !(_vmx_pin_based_exec_control & PIN_BASED_POSTED_INTERRUPT) )

With the placement of the && here corrected (belongs on the
earlier line), which can be done while committing of no other
need for v5 arises,
Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>

Jan


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