linux-kernel - Re: [PATCH 1/1] PCI: Do not size non-existing prefetchable window

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Message-ID: <20251027231222.GA1487591@bhelgaas>
Date: Mon, 27 Oct 2025 18:12:22 -0500
From: Bjorn Helgaas <helgaas@...nel.org>
To: Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>
Cc: Klaus Kudielka <klaus.kudielka@...il.com>,
	Bjorn Helgaas <bhelgaas@...gle.com>, linux-pci@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/1] PCI: Do not size non-existing prefetchable window

On Mon, Oct 27, 2025 at 03:24:23PM +0200, Ilpo Järvinen wrote:
> pbus_size_mem() should only be called for bridge windows that exist but
> __pci_bus_size_bridges() may point 'pref' to a resource that does not
> exist (has zero flags) in case of non-root buses.
> 
> When prefetchable bridge window does not exist, the same
> non-prefetchable bridge window is sized more than once which may result
> in duplicating entries into the realloc_head list. Duplicated entries
> are shown in this log and trigger a WARN_ON() because realloc_head had
> residual entries after the resource assignment algorithm:
> 
> pci 0000:00:03.0: [11ab:6820] type 01 class 0x060400 PCIe Root Port
> pci 0000:00:03.0: PCI bridge to [bus 00]
> pci 0000:00:03.0:   bridge window [io  0x0000-0x0fff]
> pci 0000:00:03.0:   bridge window [mem 0x00000000-0x000fffff]
> pci 0000:00:03.0: bridge window [mem 0x00200000-0x003fffff] to [bus 02] add_size 200000 add_align 200000
> pci 0000:00:03.0: bridge window [mem 0x00200000-0x003fffff] to [bus 02] add_size 200000 add_align 200000
> pci 0000:00:03.0: bridge window [mem 0xe0000000-0xe03fffff]: assigned
> pci 0000:00:03.0: PCI bridge to [bus 02]
> pci 0000:00:03.0:   bridge window [mem 0xe0000000-0xe03fffff]
> ------------[ cut here ]------------
> WARNING: CPU: 0 PID: 1 at drivers/pci/setup-bus.c:2373 pci_assign_unassigned_root_bus_resources+0x1bc/0x234
> 
> Check resource flags of 'pref' and only size the prefetchable window if
> the resource has the IORESOURCE_PREFETCH flag.
> 
> Fixes: ae88d0b9c57f ("PCI: Use pbus_select_window_for_type() during mem window sizing")
> Link: https://lore.kernel.org/linux-pci/51e8cf1c62b8318882257d6b5a9de7fdaaecc343.camel@gmail.com/
> Reported-by: Klaus Kudielka <klaus.kudielka@...il.com>
> Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>

Since ae88d0b9c57f appeared in v6.18-rc1, this looks like v6.18
material, right?

Applied to pci/for-linus for v6.18 on that assumption, thanks!

> ---
>  drivers/pci/setup-bus.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/pci/setup-bus.c b/drivers/pci/setup-bus.c
> index 362ad108794d..7cb6071cff7a 100644
> --- a/drivers/pci/setup-bus.c
> +++ b/drivers/pci/setup-bus.c
> @@ -1604,7 +1604,7 @@ void __pci_bus_size_bridges(struct pci_bus *bus, struct list_head *realloc_head)
>  		pbus_size_io(bus, realloc_head ? 0 : additional_io_size,
>  			     additional_io_size, realloc_head);
>  
> -		if (pref) {
> +		if (pref && (pref->flags & IORESOURCE_PREFETCH)) {
>  			pbus_size_mem(bus,
>  				      IORESOURCE_MEM | IORESOURCE_PREFETCH |
>  				      (pref->flags & IORESOURCE_MEM_64),
> 
> base-commit: 2f2c7254931f41b5736e3ba12aaa9ac1bbeeeb92
> -- 
> 2.39.5
>