Re: [PATCH 1/1] PCI: Do not add hotplug reservation multiple times

[Bjorn Helgaas]

On Mon, Jul 20, 2026 at 07:24:15PM +0300, Ilpo Järvinen wrote:
> In nested topologies, hotplug reservations gets added multiple times
> into the bridge window higher up in the hierarchy. Adding reservation
> for intermediate level bridges does not seem very useful because the
> hotplug is going to add device at a leaf.
> 
> Accounting the hoptlug reservation multiple times results in larger
> than expected bridge window size that may lead to assignment failures
> as show in this log:
> 
> pci_bus 0000:0a: root bus resource [mem 0x10a00000-0x10c00fff window]
> pci 0000:0a:00.0: BAR 0 [mem 0x10c00000-0x10c00fff]
> pci 0000:0a:00.0:   bridge window [mem 0x10a00000-0x10bfffff]
> pci 0000:0b:00.0:   bridge window [mem 0x10a00000-0x10bfffff]
> pci 0000:0c:02.0:   bridge window [mem 0x10a00000-0x10bfffff]
> pci 0000:0c:02.0: bridge window [mem 0x00100000-0x000fffff 64bit pref] to [bus 0d] add_size 200000 add_align 100000
> pci 0000:0c:02.0: bridge window [mem 0x00100000-0x000fffff] to [bus 0d] add_size 200000 add_align 100000
> pci 0000:0b:00.0: bridge window [mem 0x00100000-0x000fffff 64bit pref] to [bus 0c-0d] add_size 200000 add_align 100000
> pci 0000:0b:00.0: bridge window [mem 0x00100000-0x000fffff] to [bus 0c-0d] add_size 200000 add_align 100000
> pci 0000:0a:00.0: bridge window [mem 0x00100000-0x000fffff 64bit pref] to [bus 0b-0d] add_size 400000 add_align 100000
> pci 0000:0a:00.0: bridge window [mem 0x00100000-0x000fffff] to [bus 0b-0d] add_size 400000 add_align 100000
> pci 0000:0a:00.0: bridge window [mem size 0x00400000]: can't assign; no space
> pci 0000:0a:00.0: bridge window [mem size 0x00400000]: failed to assign
> pci 0000:0a:00.0: bridge window [mem size 0x00400000 64bit pref]: can't assign; no space
> pci 0000:0a:00.0: bridge window [mem size 0x00400000 64bit pref]: failed to assign
> 
> The problem stems from calculate_memsize() that calculates size first
> and then adds childen size:
> 	size = max(0, 2M) + 2M
> 
> Alter the logic to first account for the children size before applying
> the hotplug reservation to not add hotplug reservation multiple times
> on different levels of a nested topology. As a result, the size
> calculation becomes:
> 	size = max(0 + 2M, 2M)
> 
> Reported-by: Eric Auger <eauger@xxxxxxxxxx>
> Link: https://lore.kernel.org/linux-pci/f23946f2-06ac-4607-8f2c-3ffbc52b627a@xxxxxxxxxx/
> Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@xxxxxxxxxxxxxxx>

Applied to pci/resource for v7.3, 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 c0a949f2c995..e8c94aa1d3c1 100644
> --- a/drivers/pci/setup-bus.c
> +++ b/drivers/pci/setup-bus.c
> @@ -1021,7 +1021,7 @@ static resource_size_t calculate_memsize(resource_size_t size,
>  					 resource_size_t children_add_size,
>  					 resource_size_t align)
>  {
> -	size = max(size, min_size) + children_add_size;
> +	size = max(size + children_add_size, min_size);
>  	return ALIGN(size, align);
>  }
>  
> 
> base-commit: dc59e4fea9d83f03bad6bddf3fa2e52491777482
> -- 
> 2.47.3
>