Messages in this thread | | | Date | Tue, 11 Dec 2018 14:01:13 -0500 | From | "Michael S. Tsirkin" <> | Subject | Re: [PATCH] pci: avoid bridge feature re-probing on hotplug |
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On Tue, Dec 11, 2018 at 08:18:08AM -0600, Bjorn Helgaas wrote: > Hi Michael, > > Please run "git log --oneline drivers/pci/setup-bus.c" and follow > the usual style. > > On Mon, Dec 10, 2018 at 09:18:40PM -0500, Michael S. Tsirkin wrote: > > 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. > > Use conventional SHA1 reference (12-char SHA1). > > > Unfortunately this probing is destructive if any device behind > > the bridge is in use at this time. > > Agreed, this sounds like a problem. > > > 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. > > s/regiters/registers/
Will address above.
> > Avoiding repeated calls to pci_bridge_check_ranges might be even nicer > > would be a bigger patch and probably not appropriate on stable. > > Maybe so. The ideal thing might be to have a trivial patch like this > that can be marked for stable, immediately followed by the nicer > patch. Trivial band-aids tend to accumulate and make things harder in > the future.
I understand, and I looked at it briefly, but it's not a simple change, with probing taking detours through acpi etc.
I plan to look at it some more but should we release another linux with this bug?
> I'd have to take a much harder look at the problem to understand > 1f82de10d6b1. The comment about "double check" seems misleading -- as > you say, the hardware doesn't change and checking once should be > enough. And if we're calling pci_bridge_check_ranges() more than > necessary, that sounds like a problem, too.
So that will kind of make it a non issue. Should we still worry?
> > 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> > > --- > > > > This issue has been reported on upstream Linux and Centos. > > Are there URLs to these reports that we could include in the changelog?
https://lists.gnu.org/archive/html/qemu-devel/2018-12/msg01711.html
and specifically
https://lists.gnu.org/archive/html/qemu-devel/2018-12/msg02082.html
> > 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; > > Use conventional multi-line comment style. > > This test isn't 100%: devices below the bridge could be using only IO, > or theoretically could be even using just config space. > > If it's safe to bail out if the bridge is in use, why isn't it safe to > bail out *always*? > > > b_res[1].flags |= IORESOURCE_MEM; > > > > pci_read_config_word(bridge, PCI_IO_BASE, &io); > > -- > > MST
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