[PATCH 5.9 026/152] iommu/vt-d: Dont read VCCAP register unless it exists

[Greg Kroah-Hartman]

From: David Woodhouse <dwmw@xxxxxxxxxxxx>

commit d76b42e92780c3587c1a998a3a943b501c137553 upstream.

My virtual IOMMU implementation is whining that the guest is reading a
register that doesn't exist. Only read the VCCAP_REG if the corresponding
capability is set in ECAP_REG to indicate that it actually exists.

Fixes: 3375303e8287 ("iommu/vt-d: Add custom allocator for IOASID")
Signed-off-by: David Woodhouse <dwmw@xxxxxxxxxxxx>
Reviewed-by: Liu Yi L <yi.l.liu@xxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx # v5.7+
Acked-by: Lu Baolu <baolu.lu@xxxxxxxxxxxxxxx>
Link: https://lore.kernel.org/r/de32b150ffaa752e0cff8571b17dfb1213fbe71c.camel@xxxxxxxxxxxxx
Signed-off-by: Will Deacon <will@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 drivers/iommu/intel/dmar.c  |    3 ++-
 drivers/iommu/intel/iommu.c |    4 ++--
 2 files changed, 4 insertions(+), 3 deletions(-)

--- a/drivers/iommu/intel/dmar.c
+++ b/drivers/iommu/intel/dmar.c
@@ -964,7 +964,8 @@ static int map_iommu(struct intel_iommu
 		warn_invalid_dmar(phys_addr, " returns all ones");
 		goto unmap;
 	}
-	iommu->vccap = dmar_readq(iommu->reg + DMAR_VCCAP_REG);
+	if (ecap_vcs(iommu->ecap))
+		iommu->vccap = dmar_readq(iommu->reg + DMAR_VCCAP_REG);
 
 	/* the registers might be more than one page */
 	map_size = max_t(int, ecap_max_iotlb_offset(iommu->ecap),
--- a/drivers/iommu/intel/iommu.c
+++ b/drivers/iommu/intel/iommu.c
@@ -1798,7 +1798,7 @@ static void free_dmar_iommu(struct intel
 		if (ecap_prs(iommu->ecap))
 			intel_svm_finish_prq(iommu);
 	}
-	if (ecap_vcs(iommu->ecap) && vccap_pasid(iommu->vccap))
+	if (vccap_pasid(iommu->vccap))
 		ioasid_unregister_allocator(&iommu->pasid_allocator);
 
 #endif
@@ -3177,7 +3177,7 @@ static void register_pasid_allocator(str
 	 * is active. All vIOMMU allocators will eventually be calling the same
 	 * host allocator.
 	 */
-	if (!ecap_vcs(iommu->ecap) || !vccap_pasid(iommu->vccap))
+	if (!vccap_pasid(iommu->vccap))
 		return;
 
 	pr_info("Register custom PASID allocator\n");