linux-kernel - Re: [PATCH 5.4 v3 1/1] iommu/vt-d: Fix agaw for a supported 48 bit guest address width

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Date:   Wed, 14 Apr 2021 08:41:35 +0200
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Saeed Mirzamohammadi <saeed.mirzamohammadi@...cle.com>
Cc:     saeed.mirzamohammadi@...cle.com, stable@...r.kernel.org,
        Camille Lu <camille.lu@....com>,
        Lu Baolu <baolu.lu@...ux.intel.com>,
        David Woodhouse <dwmw2@...radead.org>,
        Joerg Roedel <joro@...tes.org>,
        iommu@...ts.linux-foundation.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 5.4 v3 1/1] iommu/vt-d: Fix agaw for a supported 48 bit
 guest address width

On Mon, Apr 12, 2021 at 01:27:35PM -0700, 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 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.
> 
> Cc: stable@...r.kernel.org
> Signed-off-by: Saeed Mirzamohammadi <saeed.mirzamohammadi@...cle.com>
> Tested-by: Camille Lu <camille.lu@....com>
> Reviewed-by: Lu Baolu <baolu.lu@...ux.intel.com>
> 
> ---

Also when you resend this, please state the commit that this fixes, as
this must be a regression, right?  What kernel version did this previous
work for?

thanks,

greg k-h