Re: [PATCH] iommu/amd: Explicitly bail from enable_iommus_vapic() when in legacy mode

[Sean Christopherson <seanjc@google.com>]

On Fri, Mar 14, 2025, Sean Christopherson wrote:
> Bail early from enable_iommus_vapic() if IOMMUs are configured for either
> of the legacy modes, as it's absurdly difficult to see that
> iommu_ga_log_enable() is guaranteed to fail because iommu_init_ga_log()
> skips allocating the ga_log.
> 
> Opportunistically have iommu_ga_log_enable() WARN if it's called without
> IOMMUs being configured to support AVIC/vAPIC.
> 
> Cc: Suravee Suthikulpanit <suravee.suthikulpanit@amd.com>
> Signed-off-by: Sean Christopherson <seanjc@google.com>
> ---
>  drivers/iommu/amd/init.c | 10 ++++++----
>  1 file changed, 6 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/iommu/amd/init.c b/drivers/iommu/amd/init.c
> index cb536d372b12..05c568da589a 100644
> --- a/drivers/iommu/amd/init.c
> +++ b/drivers/iommu/amd/init.c
> @@ -931,8 +931,8 @@ static int iommu_ga_log_enable(struct amd_iommu *iommu)
>  
>  static int iommu_init_ga_log(struct amd_iommu *iommu)
>  {
> -	if (!AMD_IOMMU_GUEST_IR_VAPIC(amd_iommu_guest_ir))
> -		return 0;
> +	if (WARN_ON_ONCE(!AMD_IOMMU_GUEST_IR_VAPIC(amd_iommu_guest_ir)))
> +		return -EINVAL;
>  
>  	iommu->ga_log = iommu_alloc_pages(GFP_KERNEL, get_order(GA_LOG_SIZE));
>  	if (!iommu->ga_log)
> @@ -2863,8 +2863,10 @@ static void enable_iommus_vapic(void)
>  			return;
>  	}
>  
> -	if (AMD_IOMMU_GUEST_IR_VAPIC(amd_iommu_guest_ir) &&
> -	    !check_feature(FEATURE_GAM_VAPIC)) {
> +	if (!AMD_IOMMU_GUEST_IR_VAPIC(amd_iommu_guest_ir))
> +		return;
> +
> +	if (!check_feature(FEATURE_GAM_VAPIC)) {
>  		amd_iommu_guest_ir = AMD_IOMMU_GUEST_IR_LEGACY_GA;
>  		return;
>  	}
> 
> base-commit: ea9bd29a9c0d757b3384ae3e633e6bbaddf00725
> -- 

Another ping.  This too still applies.