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Date:   Tue, 22 Jan 2019 08:53:56 -0500
From:   "Michael S. Tsirkin" <mst@...hat.com>
To:     xuyandong <xuyandong2@...wei.com>
Cc:     Bjorn Helgaas <helgaas@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Yinghai Lu <yinghai@...nel.org>,
        Jesse Barnes <jbarnes@...tuousgeek.org>,
        "linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
        Sagi Grimberg <sagi@...mberg.me>,
        Ofer Hayut <ofer@...htbitslabs.com>,
        Roy Shterman <roys@...htbitslabs.com>,
        Keith Busch <keith.busch@...el.com>,
        "Wangzhou (B)" <wangzhou1@...ilicon.com>
Subject: Re: [PATCH v3] PCI: avoid bridge feature re-probing on hotplug

Thanks a lot for the testing!
I'll play with it today hopefully.

On Tue, Jan 22, 2019 at 05:31:10AM +0000, xuyandong wrote:
> Hi Bjorn and Michael
> 
> After trying to reproduce the problem for a whole day, the bug did not show up
> any more. So I think the new patch does solve this problem.
> 
> > -----Original Message-----
> > From: Bjorn Helgaas [mailto:helgaas@...nel.org]
> > Sent: Sunday, January 20, 2019 4:13 AM
> > To: Michael S. Tsirkin <mst@...hat.com>
> > Cc: linux-kernel@...r.kernel.org; xuyandong <xuyandong2@...wei.com>;
> > Yinghai Lu <yinghai@...nel.org>; Jesse Barnes <jbarnes@...tuousgeek.org>;
> > linux-pci@...r.kernel.org; Sagi Grimberg <sagi@...mberg.me>; Ofer Hayut
> > <ofer@...htbitslabs.com>; Roy Shterman <roys@...htbitslabs.com>; Keith
> > Busch <keith.busch@...el.com>; Wangzhou (B) <wangzhou1@...ilicon.com>
> > Subject: [PATCH v3] PCI: avoid bridge feature re-probing on hotplug
> > 
> > I gave up trying to reproduce the problem and test this patch with qemu; can
> > you guys (Michael and Xu (sorry if I mangled your name)) give this a try?
> > 
> > I cc'd a few other people who have noticed this issue in the past, so just FYI for
> > them.
> > 
> > Bjorn
> > 
> > 
> > commit dd21b922db366ba069291b6fef2a8ce6768756a2
> > Author: Bjorn Helgaas <bhelgaas@...gle.com>
> > Date:   Sat Jan 19 11:35:04 2019 -0600
> > 
> >     PCI: Probe bridge window attributes once at enumeration-time
> > 
> >     pci_bridge_check_ranges() determines whether a bridge supports the
> > optional
> >     I/O and prefetchable memory windows and sets the flag bits in the bridge
> >     resources.  This could be done once during enumeration except that the
> >     resource allocation code completely clears the flag bits, e.g., in the
> >     pci_assign_unassigned_bridge_resources() path.
> > 
> >     The problem was that in some cases pci_bridge_check_ranges() *changes*
> > the
> >     window registers to determine whether they're writable, and this may break
> >     concurrent accesses to devices behind the bridge.
> > 
> >     Add a new pci_read_bridge_windows() to determine whether a bridge
> > supports
> >     the optional windows, call it once during enumeration, remember the
> >     results, and change pci_bridge_check_ranges() to set the flag bits based on
> >     those remembered results.
> > 
> >     Link: https://lore.kernel.org/linux-pci/1506151482-113560-1-git-send-email-
> > wangzhou1@...ilicon.com
> >     Link: https://lists.gnu.org/archive/html/qemu-devel/2018-12/msg02082.html
> >     Reported-by: xuyandong <xuyandong2@...wei.com>
> >     Cc: Sagi Grimberg <sagi@...mberg.me>
> >     Cc: Ofer Hayut <ofer@...htbitslabs.com>
> >     Cc: Roy Shterman <roys@...htbitslabs.com>
> >     Cc: Keith Busch <keith.busch@...el.com>
> >     Cc: Zhou Wang <wangzhou1@...ilicon.com>
> > 
> > diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c index
> > 257b9f6f2ebb..2ef8b954c65a 100644
> > --- a/drivers/pci/probe.c
> > +++ b/drivers/pci/probe.c
> > @@ -348,6 +348,57 @@ static void pci_read_bases(struct pci_dev *dev,
> > unsigned int howmany, int rom)
> >  	}
> >  }
> > 
> > +static void pci_read_bridge_windows(struct pci_dev *bridge) {
> > +	u16 io;
> > +	u32 pmem, tmp;
> > +
> > +	pci_read_config_word(bridge, PCI_IO_BASE, &io);
> > +	if (!io) {
> > +		pci_write_config_word(bridge, PCI_IO_BASE, 0xe0f0);
> > +		pci_read_config_word(bridge, PCI_IO_BASE, &io);
> > +		pci_write_config_word(bridge, PCI_IO_BASE, 0x0);
> > +	}
> > +	if (io)
> > +		bridge->io_window = 1;
> > +
> > +	/*
> > +	 * DECchip 21050 pass 2 errata: the bridge may miss an address
> > +	 * disconnect boundary by one PCI data phase.  Workaround: do not
> > +	 * use prefetching on this device.
> > +	 */
> > +	if (bridge->vendor == PCI_VENDOR_ID_DEC && bridge->device ==
> > 0x0001)
> > +		return;
> > +
> > +	pci_read_config_dword(bridge, PCI_PREF_MEMORY_BASE, &pmem);
> > +	if (!pmem) {
> > +		pci_write_config_dword(bridge, PCI_PREF_MEMORY_BASE,
> > +					       0xffe0fff0);
> > +		pci_read_config_dword(bridge, PCI_PREF_MEMORY_BASE,
> > &pmem);
> > +		pci_write_config_dword(bridge, PCI_PREF_MEMORY_BASE,
> > 0x0);
> > +	}
> > +	if (!pmem)
> > +		return;
> > +
> > +	bridge->pref_window = 1;
> > +
> > +	if ((pmem & PCI_PREF_RANGE_TYPE_MASK) ==
> > PCI_PREF_RANGE_TYPE_64) {
> > +
> > +		/*
> > +		 * Bridge claims to have a 64-bit prefetchable memory
> > +		 * window; verify that the upper bits are actually
> > +		 * writable.
> > +		 */
> > +		pci_read_config_dword(bridge, PCI_PREF_BASE_UPPER32,
> > &pmem);
> > +		pci_write_config_dword(bridge, PCI_PREF_BASE_UPPER32,
> > +				       0xffffffff);
> > +		pci_read_config_dword(bridge, PCI_PREF_BASE_UPPER32,
> > &tmp);
> > +		pci_write_config_dword(bridge, PCI_PREF_BASE_UPPER32,
> > pmem);
> > +		if (tmp)
> > +			bridge->pref_64_window = 1;
> > +	}
> > +}
> > +
> >  static void pci_read_bridge_io(struct pci_bus *child)  {
> >  	struct pci_dev *dev = child->self;
> > @@ -1739,6 +1790,7 @@ int pci_setup_device(struct pci_dev *dev)
> >  		pci_read_irq(dev);
> >  		dev->transparent = ((dev->class & 0xff) == 1);
> >  		pci_read_bases(dev, 2, PCI_ROM_ADDRESS1);
> > +		pci_read_bridge_windows(dev);
> >  		set_pcie_hotplug_bridge(dev);
> >  		pos = pci_find_capability(dev, PCI_CAP_ID_SSVID);
> >  		if (pos) {
> > diff --git a/drivers/pci/setup-bus.c b/drivers/pci/setup-bus.c index
> > ed960436df5e..1941bb0a6c13 100644
> > --- a/drivers/pci/setup-bus.c
> > +++ b/drivers/pci/setup-bus.c
> > @@ -735,58 +735,21 @@ int pci_claim_bridge_resource(struct pci_dev
> > *bridge, int i)
> >     base/limit registers must be read-only and read as 0. */  static void
> > pci_bridge_check_ranges(struct pci_bus *bus)  {
> > -	u16 io;
> > -	u32 pmem;
> >  	struct pci_dev *bridge = bus->self;
> > -	struct resource *b_res;
> > +	struct resource *b_res = &bridge->resource[PCI_BRIDGE_RESOURCES];
> > 
> > -	b_res = &bridge->resource[PCI_BRIDGE_RESOURCES];
> >  	b_res[1].flags |= IORESOURCE_MEM;
> > 
> > -	pci_read_config_word(bridge, PCI_IO_BASE, &io);
> > -	if (!io) {
> > -		pci_write_config_word(bridge, PCI_IO_BASE, 0xe0f0);
> > -		pci_read_config_word(bridge, PCI_IO_BASE, &io);
> > -		pci_write_config_word(bridge, PCI_IO_BASE, 0x0);
> > -	}
> > -	if (io)
> > +	if (bridge->io_window)
> >  		b_res[0].flags |= IORESOURCE_IO;
> > 
> > -	/*  DECchip 21050 pass 2 errata: the bridge may miss an address
> > -	    disconnect boundary by one PCI data phase.
> > -	    Workaround: do not use prefetching on this device. */
> > -	if (bridge->vendor == PCI_VENDOR_ID_DEC && bridge->device ==
> > 0x0001)
> > -		return;
> > -
> > -	pci_read_config_dword(bridge, PCI_PREF_MEMORY_BASE, &pmem);
> > -	if (!pmem) {
> > -		pci_write_config_dword(bridge, PCI_PREF_MEMORY_BASE,
> > -					       0xffe0fff0);
> > -		pci_read_config_dword(bridge, PCI_PREF_MEMORY_BASE,
> > &pmem);
> > -		pci_write_config_dword(bridge, PCI_PREF_MEMORY_BASE,
> > 0x0);
> > -	}
> > -	if (pmem) {
> > +	if (bridge->pref_window) {
> >  		b_res[2].flags |= IORESOURCE_MEM |
> > IORESOURCE_PREFETCH;
> > -		if ((pmem & PCI_PREF_RANGE_TYPE_MASK) ==
> > -		    PCI_PREF_RANGE_TYPE_64) {
> > +		if (bridge->pref_64_window) {
> >  			b_res[2].flags |= IORESOURCE_MEM_64;
> >  			b_res[2].flags |= PCI_PREF_RANGE_TYPE_64;
> >  		}
> >  	}
> > -
> > -	/* double check if bridge does support 64 bit pref */
> > -	if (b_res[2].flags & IORESOURCE_MEM_64) {
> > -		u32 mem_base_hi, tmp;
> > -		pci_read_config_dword(bridge, PCI_PREF_BASE_UPPER32,
> > -					 &mem_base_hi);
> > -		pci_write_config_dword(bridge, PCI_PREF_BASE_UPPER32,
> > -					       0xffffffff);
> > -		pci_read_config_dword(bridge, PCI_PREF_BASE_UPPER32,
> > &tmp);
> > -		if (!tmp)
> > -			b_res[2].flags &= ~IORESOURCE_MEM_64;
> > -		pci_write_config_dword(bridge, PCI_PREF_BASE_UPPER32,
> > -				       mem_base_hi);
> > -	}
> >  }
> > 
> >  /* Helper function for sizing routines: find first available diff --git
> > a/include/linux/pci.h b/include/linux/pci.h index 65f1d8c2f082..40b327b814aa
> > 100644
> > --- a/include/linux/pci.h
> > +++ b/include/linux/pci.h
> > @@ -373,6 +373,9 @@ struct pci_dev {
> >  	bool		match_driver;		/* Skip attaching driver */
> > 
> >  	unsigned int	transparent:1;		/* Subtractive decode bridge
> > */
> > +	unsigned int	io_window:1;		/* Bridge has I/O window */
> > +	unsigned int	pref_window:1;		/* Bridge has pref mem
> > window */
> > +	unsigned int	pref_64_window:1;	/* Pref mem window is 64-bit
> > */
> >  	unsigned int	multifunction:1;	/* Multi-function device */
> > 
> >  	unsigned int	is_busmaster:1;		/* Is busmaster */

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