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

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Date:   Wed, 7 Apr 2021 09:43:50 +0800
From:   Lu Baolu <baolu.lu@...ux.intel.com>
To:     Saeed Mirzamohammadi <saeed.mirzamohammadi@...cle.com>
Cc:     baolu.lu@...ux.intel.com, Camille Lu <camille.lu@....com>,
        David Woodhouse <dwmw2@...radead.org>,
        Joerg Roedel <joro@...tes.org>,
        iommu@...ts.linux-foundation.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v5.4 1/1] iommu/vt-d: Fix agaw for a supported 48 bit
 guest address width

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@...cle.com>
> Tested-by: Camille Lu <camille.lu@....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;

Best regards,
baolu

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