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

[Joerg Roedel]

Vasant, could you please have a look? I'd prefer a review from you or Suravee
before applying.

Thanks,

	Joerg

On Mon, Apr 06, 2026 at 04:05:09PM -0700, Sean Christopherson wrote:
> 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@xxxxxxx>
> > Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx>
> > ---
> >  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.