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Subject: Re: [PATCH] iommu: check for the deferred attach when attaching a
 device
From:   lijiang <lijiang@redhat.com>
To:     linux-kernel@vger.kernel.org
Cc:     joro@8bytes.org, will@kernel.org, iommu@lists.linux-foundation.org,
        jroedel@suse.de
References: <20201226053959.4222-1-lijiang@redhat.com>
Message-ID: <33b6f925-71e6-5d9e-74c3-3e1eaf13398e@redhat.com>
Date:   Tue, 5 Jan 2021 11:55:09 +0800
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Hi,

Also add Joerg to cc list.

Thanks.
Lianbo
在 2020年12月26日 13:39, Lianbo Jiang 写道:
> Currently, because domain attach allows to be deferred from iommu
> driver to device driver, and when iommu initializes, the devices
> on the bus will be scanned and the default groups will be allocated.
> 
> Due to the above changes, some devices could be added to the same
> group as below:
> 
> [    3.859417] pci 0000:01:00.0: Adding to iommu group 16
> [    3.864572] pci 0000:01:00.1: Adding to iommu group 16
> [    3.869738] pci 0000:02:00.0: Adding to iommu group 17
> [    3.874892] pci 0000:02:00.1: Adding to iommu group 17
> 
> But when attaching these devices, it doesn't allow that a group has
> more than one device, otherwise it will return an error. This conflicts
> with the deferred attaching. Unfortunately, it has two devices in the
> same group for my side, for example:
> 
> [    9.627014] iommu_group_device_count(): device name[0]:0000:01:00.0
> [    9.633545] iommu_group_device_count(): device name[1]:0000:01:00.1
> ...
> [   10.255609] iommu_group_device_count(): device name[0]:0000:02:00.0
> [   10.262144] iommu_group_device_count(): device name[1]:0000:02:00.1
> 
> Finally, which caused the failure of tg3 driver when tg3 driver calls
> the dma_alloc_coherent() to allocate coherent memory in the tg3_test_dma().
> 
> [    9.660310] tg3 0000:01:00.0: DMA engine test failed, aborting
> [    9.754085] tg3: probe of 0000:01:00.0 failed with error -12
> [    9.997512] tg3 0000:01:00.1: DMA engine test failed, aborting
> [   10.043053] tg3: probe of 0000:01:00.1 failed with error -12
> [   10.288905] tg3 0000:02:00.0: DMA engine test failed, aborting
> [   10.334070] tg3: probe of 0000:02:00.0 failed with error -12
> [   10.578303] tg3 0000:02:00.1: DMA engine test failed, aborting
> [   10.622629] tg3: probe of 0000:02:00.1 failed with error -12
> 
> In addition, the similar situations also occur in other drivers such
> as the bnxt_en driver. That can be reproduced easily in kdump kernel
> when SME is active.
> 
> Add a check for the deferred attach in the iommu_attach_device() and
> allow to attach the deferred device regardless of how many devices
> are in a group.
> 
> Signed-off-by: Lianbo Jiang <lijiang@redhat.com>
> ---
>  drivers/iommu/iommu.c | 5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
> index ffeebda8d6de..dccab7b133fb 100644
> --- a/drivers/iommu/iommu.c
> +++ b/drivers/iommu/iommu.c
> @@ -1967,8 +1967,11 @@ int iommu_attach_device(struct iommu_domain *domain, struct device *dev)
>  	 */
>  	mutex_lock(&group->mutex);
>  	ret = -EINVAL;
> -	if (iommu_group_device_count(group) != 1)
> +	if (!iommu_is_attach_deferred(domain, dev) &&
> +	    iommu_group_device_count(group) != 1) {
> +		dev_err_ratelimited(dev, "Group has more than one device\n");
>  		goto out_unlock;
> +	}
>  
>  	ret = __iommu_attach_group(domain, group);
>  
>