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

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

On Mon, Aug 16, 2021 at 07:39:32PM +0800, Lu Baolu wrote:
> From: Saeed Mirzamohammadi <saeed.mirzamohammadi@oracle.com>
> 
> [ Upstream commit 327d5b2fee91c404a3956c324193892cf2cc9528 ]
> 
> 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 minimum of supported adjusted guest
> address width (SAGAW) and MGAW.
> 
> 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 minimum of IOMMU's sagaw value and MGAW.
> 
> This issue happens on the code path of getting a private domain for a
> device. A private domain was needed when the domain of an iommu group
> couldn't meet the requirement of a device. The IOMMU core has been
> evolved to eliminate the need for private domain, hence this code path
> has alreay been removed from the upstream since commit 327d5b2fee91c
> ("iommu/vt-d: Allow 32bit devices to uses DMA domain"). Instead of back
> porting all patches that are required for removing the private domain,
> this simply fixes it in the affected stable kernel between v4.16 and v5.7.
> 
> [baolu: The orignal patch could be found here
>  https://lore.kernel.org/linux-iommu/20210412202736.70765-1-saeed.mirzamohammadi@oracle.com/.
>  I added commit message according to Greg's comments at
>  https://lore.kernel.org/linux-iommu/YHZ%2FT9x7Xjf1r6fI@kroah.com/.]
> 
> Cc: Joerg Roedel <joro@8bytes.org>
> Cc: Ashok Raj <ashok.raj@intel.com>
> Cc: stable@vger.kernel.org #v4.16+
> Signed-off-by: Saeed Mirzamohammadi <saeed.mirzamohammadi@oracle.com>
> Tested-by: Camille Lu <camille.lu@hpe.com>
> Signed-off-by: Lu Baolu <baolu.lu@linux.intel.com>
> ---
>  drivers/iommu/intel-iommu.c | 7 ++++---
>  1 file changed, 4 insertions(+), 3 deletions(-)

What stable tree(s) is this backport for?

thanks,

greg k-h