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

["Michael S. Tsirkin" <mst@redhat.com>]

On Tue, Dec 11, 2018 at 02:45:44AM +0000, xuyandong wrote:
> 
> 
> > -----Original Message-----
> > From: Michael S. Tsirkin [mailto:mst@redhat.com]
> > Sent: Tuesday, December 11, 2018 10:19 AM
> > To: linux-kernel@vger.kernel.org
> > Cc: xuyandong <xuyandong2@huawei.com>; stable@vger.kernel.org; Yinghai
> > Lu <yinghai@kernel.org>; Jesse Barnes <jbarnes@virtuousgeek.org>; Bjorn
> > Helgaas <bhelgaas@google.com>; linux-pci@vger.kernel.org
> > 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@huawei.com>
> > Cc: stable@vger.kernel.org
> > Cc: Yinghai Lu <yinghai@kernel.org>
> > Cc: Jesse Barnes <jbarnes@virtuousgeek.org>
> > Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
> 
> Tested-by: xuyandong <xuyandong2@huawei.com>

Bjorn could you queue this for this release?

> > ---
> > 
> > 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