RE: [PATCH 3/3] VT-d: conditionalize IOTLB register offset check

[Tian, Kevin]

> From: Jan Beulich 
> Sent: Tuesday, November 23, 2021 9:40 PM
> 
> As of commit 6773b1a7584a ("VT-d: Don't assume register-based
> invalidation is always supported") we don't (try to) use register based
> invalidation anymore when that's not supported by hardware. Hence
> there's also no point in the respective check, avoiding pointless IOMMU
> initialization failure. After all the spec (version 3.3 at the time of
> writing) doesn't say what the respective Extended Capability Register
> field would contain in such a case.
> 
> Signed-off-by: Jan Beulich 

Reviewed-by: Kevin Tian 

> 
> --- a/xen/drivers/passthrough/vtd/iommu.c
> +++ b/xen/drivers/passthrough/vtd/iommu.c
> @@ -1228,7 +1228,8 @@ int __init iommu_alloc(struct acpi_drhd_
> 
>  if ( cap_fault_reg_offset(iommu->cap) +
>   cap_num_fault_regs(iommu->cap) * PRIMARY_FAULT_REG_LEN >
> PAGE_SIZE ||
> - ecap_iotlb_offset(iommu->ecap) >= PAGE_SIZE )
> + (has_register_based_invalidation(iommu) &&
> +  ecap_iotlb_offset(iommu->ecap) >= PAGE_SIZE) )
>  {
>  printk(XENLOG_ERR VTDPREFIX "IOMMU: unsupported\n");
>  print_iommu_regs(drhd);

[PATCH 3/3] VT-d: conditionalize IOTLB register offset check

[Jan Beulich]

As of commit 6773b1a7584a ("VT-d: Don't assume register-based
invalidation is always supported") we don't (try to) use register based
invalidation anymore when that's not supported by hardware. Hence
there's also no point in the respective check, avoiding pointless IOMMU
initialization failure. After all the spec (version 3.3 at the time of
writing) doesn't say what the respective Extended Capability Register
field would contain in such a case.

Signed-off-by: Jan Beulich 

--- a/xen/drivers/passthrough/vtd/iommu.c
+++ b/xen/drivers/passthrough/vtd/iommu.c
@@ -1228,7 +1228,8 @@ int __init iommu_alloc(struct acpi_drhd_
 
 if ( cap_fault_reg_offset(iommu->cap) +
  cap_num_fault_regs(iommu->cap) * PRIMARY_FAULT_REG_LEN > PAGE_SIZE ||
- ecap_iotlb_offset(iommu->ecap) >= PAGE_SIZE )
+ (has_register_based_invalidation(iommu) &&
+  ecap_iotlb_offset(iommu->ecap) >= PAGE_SIZE) )
 {
 printk(XENLOG_ERR VTDPREFIX "IOMMU: unsupported\n");
 print_iommu_regs(drhd);