Re: [PATCH v5.4 1/1] iommu/vt-d: Fix agaw for a supported 48 bit guest address width

[Saeed Mirzamohammadi <saeed.mirzamohammadi@oracle.com>]

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Hi Lu,


On Apr 6, 2021, at 6:43 PM, Lu Baolu <baolu.lu@linux.intel.com<mailto:baolu.lu@linux.intel.com>> wrote:

Hi Saeed,

On 4/7/21 12:35 AM, Saeed Mirzamohammadi wrote:
The IOMMU driver calculates the guest addressability for a DMA request
based on the value of the mgaw reported from the IOMMU. However, this
is a fused value and as mentioned in the spec, the guest width
should be calculated based on the supported adjusted guest address width
(SAGAW).
This is from specification:
"Guest addressability for a given DMA request is limited to the
minimum of the value reported through this field and the adjusted
guest address width of the corresponding page-table structure.
(Adjusted guest address widths supported by hardware are reported
through the SAGAW field)."
This causes domain initialization to fail and following
errors appear for EHCI PCI driver:
[    2.486393] ehci-pci 0000:01:00.4: EHCI Host Controller
[    2.486624] ehci-pci 0000:01:00.4: new USB bus registered, assigned bus
number 1
[    2.489127] ehci-pci 0000:01:00.4: DMAR: Allocating domain failed
[    2.489350] ehci-pci 0000:01:00.4: DMAR: 32bit DMA uses non-identity
mapping
[    2.489359] ehci-pci 0000:01:00.4: can't setup: -12
[    2.489531] ehci-pci 0000:01:00.4: USB bus 1 deregistered
[    2.490023] ehci-pci 0000:01:00.4: init 0000:01:00.4 fail, -12
[    2.490358] ehci-pci: probe of 0000:01:00.4 failed with error -12
This issue happens when the value of the sagaw corresponds to a
48-bit agaw. This fix updates the calculation of the agaw based on
the IOMMU's sagaw value.
Signed-off-by: Saeed Mirzamohammadi <saeed.mirzamohammadi@oracle.com<mailto:saeed.mirzamohammadi@oracle.com>>
Tested-by: Camille Lu <camille.lu@hpe.com<mailto:camille.lu@hpe.com>>
---
 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 953d86ca6d2b..396e14fad54b 100644
--- a/drivers/iommu/intel-iommu.c
+++ b/drivers/iommu/intel-iommu.c
@@ -1867,8 +1867,8 @@ 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);

The spec requires to use a minimum of MGAW and AGAW, so why not,

cap_width = min_t(int, cap_mgaw(iommu->cap), agaw_to_width(iommu->agaw));
if (guest_width > cap_width)
guest_width = cap_width;

Yes, this works better. I just sent the v2.

Thanks,
Saeed


Best regards,
baolu

  domain->gaw = guest_width;
  adjust_width = guestwidth_to_adjustwidth(guest_width);
  agaw = width_to_agaw(adjust_width);


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