Re: [PATCH 06/67] iommu/amd: WARN if KVM attempts to set vCPU affinity without posted intrrupts

[Sairaj Kodilkar]

On 4/5/2025 1:08 AM, Sean Christopherson wrote:
> WARN if KVM attempts to set vCPU affinity when posted interrupts aren't
> enabled, as KVM shouldn't try to enable posting when they're unsupported,
> and the IOMMU driver darn well should only advertise posting support when
> AMD_IOMMU_GUEST_IR_VAPIC() is true.
>
> Note, KVM consumes is_guest_mode only on success.
>
> Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx>
> ---
>   drivers/iommu/amd/iommu.c | 13 +++----------
>   1 file changed, 3 insertions(+), 10 deletions(-)
>
> diff --git a/drivers/iommu/amd/iommu.c b/drivers/iommu/amd/iommu.c
> index b3a01b7757ee..4f69a37cf143 100644
> --- a/drivers/iommu/amd/iommu.c
> +++ b/drivers/iommu/amd/iommu.c
> @@ -3852,19 +3852,12 @@ static int amd_ir_set_vcpu_affinity(struct irq_data *data, void *vcpu_info)
>   	if (!dev_data || !dev_data->use_vapic)
>   		return -EINVAL;
>   
> +	if (WARN_ON_ONCE(!AMD_IOMMU_GUEST_IR_VAPIC(amd_iommu_guest_ir)))
> +		return -EINVAL;
> +

Hi Sean,
'dev_data->use_vapic' is always zero when AMD IOMMU uses legacy
interrupts i.e. when AMD_IOMMU_GUEST_IR_VAPIC(amd_iommu_guest_ir) is 0.
Hence you can remove this additional check.

Regards
Sairaj Kodilkar

>   	ir_data->cfg = irqd_cfg(data);
>   	pi_data->ir_data = ir_data;
>   
> -	/* Note:
> -	 * SVM tries to set up for VAPIC mode, but we are in
> -	 * legacy mode. So, we force legacy mode instead.
> -	 */
> -	if (!AMD_IOMMU_GUEST_IR_VAPIC(amd_iommu_guest_ir)) {
> -		pr_debug("%s: Fall back to using intr legacy remap\n",
> -			 __func__);
> -		pi_data->is_guest_mode = false;
> -	}
> -
>   	pi_data->prev_ga_tag = ir_data->cached_ga_tag;
>   	if (pi_data->is_guest_mode) {
>   		ir_data->ga_root_ptr = (pi_data->base >> 12);