Re: [PATCH v5 01/18] PCI: Don't suspend IOMMU when probing reset capability

[Jason Gunthorpe]

> reset_method_store() in drivers/pci/pci-sysfs.c discovers supported reset
> methods by calling reset_fn(pdev, PCI_RESET_PROBE, ...) without holding a
> device_lock, since the probe path is expected to query the device's reset
> capability without changing device state.
> 
> However, pci_reset_bus_function() and __pci_dev_specific_reset() violate
> that contract after pci_dev_reset_iommu_prepare/done() were added, which
> moves the device into a blocking domain and abruptly aborts any in-flight
> DMA. Doing this for a probe -- a state-query call that does not even hold
> device_lock -- can cause driver timeouts and data loss on a DMAing device.
> 
> The peer reset helpers all handle this correctly: they short-circuit on a
> probe input before touching the IOMMU.
> 
> Skip pci_dev_reset_iommu_prepare()/_done() entirely when probe is set. The
> inner reset routines already implement their own probe semantics, and they
> perform the capability checks and return without changing device state.
> 
> Fixes: f5b16b802174 ("PCI: Suspend iommu function prior to resetting a device")
> Cc: stable@xxxxxxxxxxxxxxx
> Assisted-by: Claude:claude-opus-4-7
> Signed-off-by: Nicolin Chen <nicolinc@xxxxxxxxxx>
>
> diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
> index 77b17b13ee6154..01cf3105405614 100644
> --- a/drivers/pci/pci.c
> +++ b/drivers/pci/pci.c
> @@ -4946,10 +4946,12 @@ static int pci_reset_bus_function(struct pci_dev *dev, bool probe)
>  	if (bridge && pcie_is_cxl(bridge) && cxl_sbr_masked(bridge))
>  		return -ENOTTY;
>  
> -	rc = pci_dev_reset_iommu_prepare(dev);
> -	if (rc) {
> -		pci_err(dev, "failed to stop IOMMU for a PCI reset: %d\n", rc);
> -		return rc;
> +	if (!probe) {

Given this is using this funny enum:

 #define PCI_RESET_PROBE		true
 #define PCI_RESET_DO_RESET	false

Was the intention to also use it to sample probe? Bit confusing

The actual change looks fine:

Reviewed-by: Jason Gunthorpe <jgg@xxxxxxxxxx>

-- 
Jason