Subject: [PATCH] iommu/arm-smmu: Fix stream-match conflict with IOMMU_DOMAIN_DMA

From: [email-masked] (Eric Auger)
Date: Mon, 4 Apr 2016 11:40:29 +0200

Hi Will,
On 04/01/2016 06:19 PM, Will Deacon wrote:
> Commit cbf8277ef456 ("iommu/arm-smmu: Treat IOMMU_DOMAIN_DMA as bypass
> for now") ignores requests to attach a device to the default domain
> since, without IOMMU-basked DMA ops available everywhere, the default
> domain will just lead to unexpected transaction faults being reported.
> 
> Unfortunately, the way this was implemented on SMMUv2 causes a
> regression with VFIO PCI device passthrough under KVM on AMD Seattle.
> On this system, the host controller device is associated with both a
> pci_dev *and* a platform_device, and can therefore end up with duplicate
> SMR entries, resulting in a stream-match conflict at runtime.
> 
> This patch amends the original fix so that attaching to IOMMU_DOMAIN_DMA
> is rejected even before configuring the SMRs. This restores the old
> behaviour for now, but we'll need to look at handing host controllers
> specially when we come to supporting the default domain fully.

This works fine for me, before and after PCIe assignment. However before
giving my T-b I would like to investigate another regression I observe
wrt SRIOV assignment. Assigning the 1st VF works fine. However assigning
a second VF does not work anymore (it used to in the past). I get
-ENOSPC from arm_smmu_master_configure_smrs

Best Regards

Eric
> 
> Reported-by: Eric Auger <[email-masked]>
> Signed-off-by: Will Deacon <[email-masked]>
> ---
>  drivers/iommu/arm-smmu.c | 14 ++++++++------
>  1 file changed, 8 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/iommu/arm-smmu.c b/drivers/iommu/arm-smmu.c
> index e933679a3266..2f186d22477f 100644
> --- a/drivers/iommu/arm-smmu.c
> +++ b/drivers/iommu/arm-smmu.c
> @@ -1098,18 +1098,20 @@ static int arm_smmu_domain_add_master(struct arm_smmu_domain *smmu_domain,
>  	struct arm_smmu_device *smmu = smmu_domain->smmu;
>  	void __iomem *gr0_base = ARM_SMMU_GR0(smmu);
>  
> -	/* Devices in an IOMMU group may already be configured */
> -	ret = arm_smmu_master_configure_smrs(smmu, cfg);
> -	if (ret)
> -		return ret == -EEXIST ? 0 : ret;
> -
>  	/*
>  	 * FIXME: This won't be needed once we have IOMMU-backed DMA ops
> -	 * for all devices behind the SMMU.
> +	 * for all devices behind the SMMU. Note that we need to take
> +	 * care configuring SMRs for devices both a platform_device and
> +	 * and a PCI device (i.e. a PCI host controller)
>  	 */
>  	if (smmu_domain->domain.type == IOMMU_DOMAIN_DMA)
>  		return 0;
>  
> +	/* Devices in an IOMMU group may already be configured */
> +	ret = arm_smmu_master_configure_smrs(smmu, cfg);
> +	if (ret)
> +		return ret == -EEXIST ? 0 : ret;
> +
>  	for (i = 0; i < cfg->num_streamids; ++i) {
>  		u32 idx, s2cr;
>  
>