Re: [PATCH] iommu/amd: Adhere to IVINFO[VASIZE] for address limits

[Jason Gunthorpe <jgg@ziepe.ca>]

On Tue, Mar 03, 2026 at 11:47:21AM +0000, Ankit Soni wrote:

> > > +	/*
> > > +	 * IVINFO[VASIZE] encodes the log2 of the maximum virtual address
> > > +	 * processed by the IOMMU.
> > > +	 */
> > > +	switch (vasize) {
> > > +	case 32:
> > > +	case 40:
> > > +	case 48:
> > > +	case 64:
> > > +		return vasize;
> > > +	default:
> > > +		pr_warn_once("IVRS: IVINFO[VASIZE]=0x%x is invalid, defaulting to 64‑bit VA\n",
> > > +			     vasize);
> > > +		return 64;
> > 
> > Why check and limit it like this? 
> > 
> 
> I’ll replace this with a macro and send that in v3. If you have other suggestions,
> I’m happy to incorporate.
> 
> > > -	cfg.common.hw_max_vasz_lg2 =
> > > -		min(64, (amd_iommu_hpt_level - 1) * 9 + 21);
> > > +	cfg.common.hw_max_vasz_lg2 = amd_iommu_hpt_vasize;
> > 
> > This has no restriction, you can send it whatever size you want.
> > 
> 
> The intent is for the kernel to respect what the VM advertises in IVINFO.
> If we ignore IVINFO[VASIZE] and use a larger limit (i.e. from EFR only),
> driver can exceed vasize what the VM allows and break the guest.

I mean if FIELD_GET(IOMMU_IVINFO_VASIZE, amd_iommu_ivinfo) is 35 why
not just pass it to hw_max_vasz_lg2 and be done with it? What is the
point of limiting to only a few values?

Jason