linux-kernel - Re: [PATCH v3 01/15] iommu/vt-d: Handle race between registration and device probe

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Message-ID: <032937a0-ffef-221c-4faf-4680fa09b2af@linux.intel.com>
Date:   Wed, 6 Jul 2022 09:39:40 +0800
From:   Baolu Lu <baolu.lu@...ux.intel.com>
To:     Robin Murphy <robin.murphy@....com>, joro@...tes.org
Cc:     baolu.lu@...ux.intel.com, will@...nel.org, iommu@...ts.linux.dev,
        linux-arm-kernel@...ts.infradead.org,
        suravee.suthikulpanit@....com, vasant.hegde@....com,
        mjrosato@...ux.ibm.com, gerald.schaefer@...ux.ibm.com,
        schnelle@...ux.ibm.com, linux-s390@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 01/15] iommu/vt-d: Handle race between registration and
 device probe

On 2022/7/6 01:08, Robin Murphy wrote:
> Currently we rely on registering all our instances before initially
> allowing any .probe_device calls via bus_set_iommu(). In preparation for
> phasing out the latter, make sure we won't inadvertently return success
> for a device associated with a known but not yet registered instance,
> otherwise we'll run straight into iommu_group_get_for_dev() trying to
> use NULL ops.
> 
> That also highlights an issue with intel_iommu_get_resv_regions() taking
> dmar_global_lock from within a section where intel_iommu_init() already
> holds it, which already exists via probe_acpi_namespace_devices() when
> an ANDD device is probed, but gets more obvious with the upcoming change
> to iommu_device_register(). Since they are both read locks it manages
> not to deadlock in practice, so I'm leaving it here for someone with
> more confidence to tackle a larger rework of the locking.

Thanks for highlighting this. I will look into it later.

Best regards,
baolu

> 
> Signed-off-by: Robin Murphy <robin.murphy@....com>
> ---
> 
> v3: New
> 
>   drivers/iommu/intel/iommu.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/iommu/intel/iommu.c b/drivers/iommu/intel/iommu.c
> index 44016594831d..3e02c08802a0 100644
> --- a/drivers/iommu/intel/iommu.c
> +++ b/drivers/iommu/intel/iommu.c
> @@ -4600,7 +4600,7 @@ static struct iommu_device *intel_iommu_probe_device(struct device *dev)
>   	u8 bus, devfn;
>   
>   	iommu = device_to_iommu(dev, &bus, &devfn);
> -	if (!iommu)
> +	if (!iommu || !iommu->iommu.ops)
>   		return ERR_PTR(-ENODEV);
>   
>   	info = kzalloc(sizeof(*info), GFP_KERNEL);