Re: [PATCH v17 12/19] PCI/CXL: Add CXL Device Reset sequencing

[Lucero Palau, Alejandro]

On 05/11/2026 18:59, Srirangan Madhavan wrote:
> Implement CXL Device Reset for eligible Type 2 devices: disable CXL.cache,
> perform supported writeback, drain transactions, prepare the IOMMU,
> initiate reset with Memory Clear enabled, and wait for completion.
>
> Observe the 100 ms post-reset quiet period before polling Status2, and
> treat an all-ones read as not ready. Wait for the timeout the device
> advertises, up to 100 seconds, and access only Status2 until reset
> completion, error or expiry, as CXL 4.0 section 9.7.3 requires. Control2
> cleanup runs only afterwards. Treat Control2 command bits as
> transient state, restore cache policy on exit, preserve the primary error,
> and abort when IOMMU preparation fails.
>
> Reuse Device DVSEC discovery from cache initialization and keep the
> reset entry point declaration private to PCI core.
>
> Signed-off-by: Srirangan Madhavan <smadhavan@xxxxxxxxxx>


Hi Srirangan,


A concern regarding IOMMU handling below. If it turns to be unfounded, 
you can add my review tag.


Thank you,

Alejandro


<snip>

> +static int __cxl_reset_execute(struct pci_dev *pdev, int dvsec, u16 cap)
> +{
> +	int rc, rc2;
> +
> +	if (!pci_wait_for_pending_transaction(pdev)) {
> +		pci_err(pdev, "timed out waiting for pending transactions\n");
> +		return -ETIMEDOUT;
> +	}
> +
> +	rc = pci_dev_reset_iommu_prepare(pdev);


I'm not sure if this is safe enough. I can see a situation where a Type2 
device could not be using CXL.mem and CXL.cache but CXL.io. This would 
imply no CXL initialization from the Type2 driver but:


    1) Such a driver could be giving functionality without CXL

    2) The device belonging to an IOMMU domain which such functionality 
is using

    3) The HDM decoder range as a system resource is free.


If I am right, a CXL reset could happen, and although it should not be 
triggered by user space under these circumstances, the door is open ...


The solution would be, currently, to check for a  driver not bound to 
the device in an IOMMU enabled system. I say currently because CXL.cache 
will need extra work with IOMMU mapping which are not yet there.