RE: [PATCH] pci: avoid bridge feature re-probing on hotplug

[xuyandong]

> -----Original Message-----
> From: Michael S. Tsirkin [mailto:mst@xxxxxxxxxx]
> Sent: Tuesday, December 11, 2018 10:19 AM
> To: linux-kernel@xxxxxxxxxxxxxxx
> Cc: xuyandong <xuyandong2@xxxxxxxxxx>; stable@xxxxxxxxxxxxxxx; Yinghai
> Lu <yinghai@xxxxxxxxxx>; Jesse Barnes <jbarnes@xxxxxxxxxxxxxxxx>; Bjorn
> Helgaas <bhelgaas@xxxxxxxxxx>; linux-pci@xxxxxxxxxxxxxxx
> Subject: [PATCH] pci: avoid bridge feature re-probing on hotplug
> 
> commit 1f82de10d6 ("PCI/x86: don't assume prefetchable ranges are
> 64bit") added probing of bridge support for 64 bit memory each time bridge is
> re-enumerated.
> 
> Unfortunately this probing is destructive if any device behind the bridge is in
> use at this time.
> 
> There's no real need to re-probe the bridge features as the regiters in question
> never change - detect that using the memory flag being set and skip the
> probing.
> Avoiding repeated calls to pci_bridge_check_ranges might be even nicer would
> be a bigger patch and probably not appropriate on stable.
> 
> Reported-by: xuyandong <xuyandong2@xxxxxxxxxx>
> Cc: stable@xxxxxxxxxxxxxxx
> Cc: Yinghai Lu <yinghai@xxxxxxxxxx>
> Cc: Jesse Barnes <jbarnes@xxxxxxxxxxxxxxxx>
> Signed-off-by: Michael S. Tsirkin <mst@xxxxxxxxxx>

Tested-by: xuyandong <xuyandong2@xxxxxxxxxx>

> ---
> 
> This issue has been reported on upstream Linux and Centos.
> 
>  drivers/pci/setup-bus.c | 7 +++++++
>  1 file changed, 7 insertions(+)
> 
> diff --git a/drivers/pci/setup-bus.c b/drivers/pci/setup-bus.c index
> ed960436df5e..7ab42f76579e 100644
> --- a/drivers/pci/setup-bus.c
> +++ b/drivers/pci/setup-bus.c
> @@ -741,6 +741,13 @@ static void pci_bridge_check_ranges(struct pci_bus
> *bus)
>  	struct resource *b_res;
> 
>  	b_res = &bridge->resource[PCI_BRIDGE_RESOURCES];
> +
> +	/* Don't re-check after this was called once already:
> +	 * important since bridge might be in use.
> +	 */
> +	if (b_res[1].flags & IORESOURCE_MEM)
> +		return;
> +
>  	b_res[1].flags |= IORESOURCE_MEM;
> 
>  	pci_read_config_word(bridge, PCI_IO_BASE, &io);
> --
> MST