Question about domain_init (v5.3-v5.7)

From: Jerry Snitselaar <jsnitsel@redhat.com>
To: Lu Baolu <baolu.lu@linux.intel.com>,
	Joerg Roedel <joro@8bytes.org>,
	iommu@lists.linux-foundation.org, linux-kernel@vger.kernel.org,
	stable@kernel.vger.org
Subject: Question about domain_init (v5.3-v5.7)
Date: Wed, 25 Nov 2020 13:27:31 -0700	[thread overview]
Message-ID: <87h7pd6v2k.fsf@redhat.com> (raw)


Is there a reason we check the requested guest address width against the
iommu's mgaw, instead of the agaw that we already know for the iommu?
I've run into a case with a new system where the mgaw reported is 57,
but if they set PAE to 46 instead of 52 in the bios, then sagaw reports
the highest supported agaw is 48 and the domain_init code fails here. In
other places like prepare_domain_attach_device, the dmar domain agaw
gets adjusted down to the iommu agaw. The agaw of the iommu gets
determined based off what is reported for sagaw. I'm wondering if it
can't instead do:

---
 drivers/iommu/intel-iommu.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/iommu/intel-iommu.c b/drivers/iommu/intel-iommu.c
index 6ca5c92ef2e5..a8e41ec36d9e 100644
--- a/drivers/iommu/intel-iommu.c
+++ b/drivers/iommu/intel-iommu.c
@@ -1862,8 +1862,8 @@ static int domain_init(struct dmar_domain *domain, struct intel_iommu *iommu,
 	domain_reserve_special_ranges(domain);

 	/* calculate AGAW */
-	if (guest_width > cap_mgaw(iommu->cap))
-	        guest_width = cap_mgaw(iommu->cap);
+	if (guest_width > agaw_to_width(iommu->agaw))
+	        guest_width = agaw_to_width(iommu->agaw);
 	domain->gaw = guest_width;
 	adjust_width = guestwidth_to_adjustwidth(guest_width);
 	agaw = width_to_agaw(adjust_width);
--
2.27.0


Thoughts? With the former code the ehci device for the ilo fails when
trying to get a private domain.

Thanks,
Jerry

