Re: [PATCH 13/23] PCI: Add pbus_mem_size_optional() to handle optional sizes

["Ilpo Järvinen" <ilpo.jarvinen@linux.intel.com>]

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On Wed, 8 Jul 2026, Eric Auger wrote:
> On 7/8/26 4:05 PM, Ilpo Järvinen wrote:
> > On Wed, 8 Jul 2026, Eric Auger wrote:
> >> On 7/7/26 6:12 PM, Ilpo Järvinen wrote:
> >>> On Tue, 7 Jul 2026, Eric Auger wrote:
> >>>
> >>>> Hi Ilpo,
> >>>>
> >>>> On 12/19/25 6:40 PM, Ilpo Järvinen wrote:
> >>>>> The resource loop in pbus_size_mem() handles optional resources that
> >>>>> are either fully optional (SRIOV and disabled Expansion ROMs) or bridge
> >>>>> windows that may be optional only for a part. The logic is little
> >>>>> inconsistent when it comes to a bridge window that has only optional
> >>>>> children resources as it would be more natural to treat it similar to
> >>>>> any fully optional resource. As resource size should be zero in that
> >>>>> case, it shouldn't cause any bugs but it still seems useful to address
> >>>>> the inconsistency.
> >>>>>
> >>>>> Place the optional size related code of pbus_size_mem() into
> >>>>> pbus_mem_size_optional() and add check into pci_resource_is_optional()
> >>>>> for entirely optional bridge windows. Reorder the logic inside
> >>>>> pbus_mem_size_optional() such that fully optional resources are handled
> >>>>> the same irrespective to whether the resource is a bridge window or
> >>>>> not.
> >>>>
> >>>> This patch seems to introduce a regression when trying to hotplug a
> >>>> virtio-net-pci device behind a XIO3130 downstream port in the following
> >>>> hierarchy.
> >>>>
> >>>> this happens with a v7.2-rc2 guest kernel, on an arm64 guest with qemu vmm.
> >>>>
> >>>>
> >>>>
> >>>> 00:01.0 Host bridge: Red Hat, Inc. QEMU PCIe Expander bridge
> >>>> 	Subsystem: Red Hat, Inc. Device 1100
> >>>>
> >>>> |_ 0a:00.0 PCI bridge: Red Hat, Inc. QEMU PCIe Root port
> >>>>    Subsystem: Red Hat, Inc. Device 0000
> >>>>    Kernel driver in use: pcieport
> >>>>
> >>>>    |_ 0b:00.0 PCI bridge: Texas Instruments XIO3130 PCI Express Switch
> >>>>
> >>>> 	(Upstream) (rev 02)
> >>>> 	Kernel driver in use: pcieport
> >>>>
> >>>> 	|_ 0c:02.0 PCI bridge: Texas Instruments XIO3130 PCI Express
> >>>> 		Switch (Downstream) (rev 01)
> >>>> 		Kernel driver in use: pcieport
> >>>
> >>> Hi Eric,
> >>>
> >>> Thanks for the report.
> >>>
> >>> I cannot get much done with the log snippets. The first line with 
> >>> difference is a symptom of something that originates from outside of the 
> >>> snippet.
> >>>
> >>> Could you please take a log with dyndbg="file drivers/pci/*.c +p" on the 
> >>> kernel command line and also include a /proc/iomem dump. Like 
> >>> you did now, preferrably take those from both working and failing case so 
> >>> I can easily diff them.
> >>>
> >>> --
> >>>  i.
> >>>
> >>>
> >>>> This produces the following trace
> >>>>
> >>>>
> >>>> [   28.557947] pcieport 0000:0c:02.0: pciehp: Slot(0-1): Card present
> >>>> [   28.557949] pcieport 0000:0c:02.0: pciehp: Slot(0-1): Link Up
> >>>> [   29.605376] pci 0000:0d:00.0: [1af4:1041] type 00 class 0x020000 PCIe
> >>>> Endpoint
> >>>> [   29.605724] pci 0000:0d:00.0: BAR 1 [mem 0x00000000-0x00000fff]
> >>>> [   29.605765] pci 0000:0d:00.0: BAR 4 [mem 0x00000000-0x00003fff 64bit
> >>>> pref]
> >>>> [   29.605816] pci 0000:0d:00.0: enabling Extended Tags
> >>>> [   29.606994] pcieport 0000:0c:02.0: bridge window [mem size 0x00100000
> >>>> 64bit pref] to [bus 0d] add_size 100000 add_align 100000
> >>>> [   29.606998] pcieport 0000:0c:02.0: bridge window [mem size
> >>>> 0x00100000] to [bus 0d] add_size 100000 add_align 100000
> >>>> [   29.607003] pcieport 0000:0c:02.0: bridge window [mem size
> >>>> 0x00200000]: can't assign; no space
> >>>> [   29.607005] pcieport 0000:0c:02.0: bridge window [mem size
> >>>> 0x00200000]: failed to assign
> >>>> [   29.607007] pcieport 0000:0c:02.0: bridge window [mem size 0x00200000
> >>>> 64bit pref]: can't assign; no space
> >>>> [   29.607008] pcieport 0000:0c:02.0: bridge window [mem size 0x00200000
> >>>> 64bit pref]: failed to assign
> >>>> [   29.607010] pcieport 0000:0c:02.0: bridge window [io  size 0x1000]:
> >>>> can't assign; no space
> >>>> [   29.607012] pcieport 0000:0c:02.0: bridge window [io  size 0x1000]:
> >>>> failed to assign
> >>>> [   29.607014] pcieport 0000:0c:02.0: bridge window [mem size
> >>>> 0x00100000]: can't assign; no space
> >>>> [   29.607016] pcieport 0000:0c:02.0: bridge window [mem size
> >>>> 0x00100000]: failed to assign
> >>>> [   29.607018] pcieport 0000:0c:02.0: bridge window [mem size 0x00100000
> >>>> 64bit pref]: can't assign; no space
> >>>> [   29.607019] pcieport 0000:0c:02.0: bridge window [mem size 0x00100000
> >>>> 64bit pref]: failed to assign
> >>>> [   29.607021] pcieport 0000:0c:02.0: bridge window [io  size 0x1000]:
> >>>> can't assign; no space
> >>>> [   29.607022] pcieport 0000:0c:02.0: bridge window [io  size 0x1000]:
> >>>> failed to assign
> >>>> [   29.607025] pci 0000:0d:00.0: BAR 4 [mem size 0x00004000 64bit pref]:
> >>>> can't assign; no space
> >>>> [   29.607026] pci 0000:0d:00.0: BAR 4 [mem size 0x00004000 64bit pref]:
> >>>> failed to assign
> >>>> [   29.607027] pci 0000:0d:00.0: BAR 1 [mem size 0x00001000]: can't
> >>>> assign; no space
> >>>> [   29.607028] pci 0000:0d:00.0: BAR 1 [mem size 0x00001000]: failed to
> >>>> assign
> >>>> [   29.607029] pci 0000:0d:00.0: BAR 4 [mem size 0x00004000 64bit pref]:
> >>>> can't assign; no space
> >>>> [   29.607030] pci 0000:0d:00.0: BAR 4 [mem size 0x00004000 64bit pref]:
> >>>> failed to assign
> >>>> [   29.607031] pci 0000:0d:00.0: BAR 1 [mem size 0x00001000]: can't
> >>>> assign; no space
> >>>> [   29.607032] pci 0000:0d:00.0: BAR 1 [mem size 0x00001000]: failed to
> >>>> assign
> >>>> [   29.607033] pcieport 0000:0c:02.0: PCI bridge to [bus 0d]
> >>>> [   29.611260] PCI: No. 2 try to assign unassigned res
> >>>> [   29.611269] pcieport 0000:0c:02.0: bridge window [mem size 0x00100000
> >>>> 64bit pref] to [bus 0d] add_size 100000 add_align 100000
> >>>> [   29.611272] pcieport 0000:0c:02.0: bridge window [mem size
> >>>> 0x00100000] to [bus 0d] add_size 100000 add_align 100000
> >>>> [   29.611276] pcieport 0000:0c:02.0: bridge window [mem size
> >>>> 0x00200000]: can't assign; no space
> >>>> [   29.611277] pcieport 0000:0c:02.0: bridge window [mem size
> >>>> 0x00200000]: failed to assign
> >>>> [   29.611278] pcieport 0000:0c:02.0: bridge window [mem size 0x00200000
> >>>> 64bit pref]: can't assign; no space
> >>>> [   29.611279] pcieport 0000:0c:02.0: bridge window [mem size 0x00200000
> >>>> 64bit pref]: failed to assign
> >>>> [   29.611280] pcieport 0000:0c:02.0: bridge window [io  size 0x1000]:
> >>>> can't assign; no space
> >>>> [   29.611280] pcieport 0000:0c:02.0: bridge window [io  size 0x1000]:
> >>>> failed to assign
> >>>> [   29.611281] pcieport 0000:0c:02.0: bridge window [mem size
> >>>> 0x00100000]: can't assign; no space
> >>>> [   29.611282] pcieport 0000:0c:02.0: bridge window [mem size
> >>>> 0x00100000]: failed to assign
> >>>> [   29.611283] pcieport 0000:0c:02.0: bridge window [mem size 0x00100000
> >>>> 64bit pref]: can't assign; no space
> >>>> [   29.611283] pcieport 0000:0c:02.0: bridge window [mem size 0x00100000
> >>>> 64bit pref]: failed to assign
> >>>> [   29.611284] pcieport 0000:0c:02.0: bridge window [io  size 0x1000]:
> >>>> can't assign; no space
> >>>> [   29.611284] pcieport 0000:0c:02.0: bridge window [io  size 0x1000]:
> >>>> failed to assign
> >>>> [   29.611286] pci 0000:0d:00.0: BAR 4 [mem size 0x00004000 64bit pref]:
> >>>> can't assign; no space
> >>>> [   29.611286] pci 0000:0d:00.0: BAR 4 [mem size 0x00004000 64bit pref]:
> >>>> failed to assign
> >>>> [   29.611287] pci 0000:0d:00.0: BAR 1 [mem size 0x00001000]: can't
> >>>> assign; no space
> >>>> [   29.611288] pci 0000:0d:00.0: BAR 1 [mem size 0x00001000]: failed to
> >>>> assign
> >>>> [   29.611288] pci 0000:0d:00.0: BAR 4 [mem size 0x00004000 64bit pref]:
> >>>> can't assign; no space
> >>>> [   29.611289] pci 0000:0d:00.0: BAR 4 [mem size 0x00004000 64bit pref]:
> >>>> failed to assign
> >>>> [   29.611289] pci 0000:0d:00.0: BAR 1 [mem size 0x00001000]: can't
> >>>> assign; no space
> >>>> [   29.611290] pci 0000:0d:00.0: BAR 1 [mem size 0x00001000]: failed to
> >>>> assign
> >>>> [   29.611291] pcieport 0000:0c:02.0: PCI bridge to [bus 0d]
> >>>> [   29.616141] ACPI: \_SB_.L0A2: Enabled at IRQ 37
> >>>> [   29.616378] virtio-pci 0000:0d:00.0: virtio_pci: leaving for legacy
> >>>> driver
> >>>>
> >>>> Previous to this commit hotplug was successful:
> >>>>
> >>>> vm-rhel10 login: [   38.385692] pcieport 0000:0c:02.0: pciehp:
> >>>> Slot(0-1): Button press: will power on in 5 sec
> >>>> [   38.385798] pcieport 0000:0c:02.0: pciehp: Slot(0-1): Card present
> >>>> [   38.385799] pcieport 0000:0c:02.0: pciehp: Slot(0-1): Link Up
> >>>> [   39.553709] pci 0000:0d:00.0: [1af4:1041] type 00 class 0x020000 PCIe
> >>>> Endpoint
> >>>> [   39.554018] pci 0000:0d:00.0: BAR 1 [mem 0x00000000-0x00000fff]
> >>>> [   39.554042] pci 0000:0d:00.0: BAR 4 [mem 0x00000000-0x00003fff 64bit
> >>>> pref]
> >>>> [   39.554099] pci 0000:0d:00.0: enabling Extended Tags
> >>>> [   39.555202] pcieport 0000:0c:02.0: bridge window [mem size 0x00100000
> >>>> 64bit pref] to [bus 0d] add_size 100000 add_align 100000
> >>>> [   39.555206] pcieport 0000:0c:02.0: bridge window [mem size
> >>>> 0x00100000] to [bus 0d] add_size 100000 add_align 100000
> >>>> [   39.555212] pcieport 0000:0c:02.0: bridge window [mem size
> >>>> 0x00200000]: can't assign; no space
> >>>> [   39.555213] pcieport 0000:0c:02.0: bridge window [mem size
> >>>> 0x00200000]: failed to assign
> >>>> [   39.555215] pcieport 0000:0c:02.0: bridge window [mem size 0x00200000
> >>>> 64bit pref]: can't assign; no space
> >>>> [   39.555216] pcieport 0000:0c:02.0: bridge window [mem size 0x00200000
> >>>> 64bit pref]: failed to assign
> >>>> [   39.555218] pcieport 0000:0c:02.0: bridge window [io  size 0x1000]:
> >>>> can't assign; no space
> >>>> [   39.555219] pcieport 0000:0c:02.0: bridge window [io  size 0x1000]:
> >>>> failed to assign
> >>>> [   39.555222] pcieport 0000:0c:02.0: bridge window [mem
> >>>> 0x10a00000-0x10afffff]: assigned
> >>>> [   39.555224] pcieport 0000:0c:02.0: bridge window [mem
> >>>> 0x10b00000-0x10bfffff 64bit pref]: assigned
> >>>> [   39.555225] pcieport 0000:0c:02.0: bridge window [io  size 0x1000]:
> >>>> can't assign; no space
> >>>> [   39.555227] pcieport 0000:0c:02.0: bridge window [io  size 0x1000]:
> >>>> failed to assign
> >>>> [   39.555228] pcieport 0000:0c:02.0: bridge window [mem
> >>>> 0x10a00000-0x10afffff]: failed to expand by 0x100000
> >>>> [   39.555230] pcieport 0000:0c:02.0: bridge window [mem
> >>>> 0x10a00000-0x10afffff]: failed to add optional 100000
> >>>> [   39.555232] pcieport 0000:0c:02.0: bridge window [mem
> >>>> 0x10b00000-0x10bfffff 64bit pref]: failed to expand by 0x100000
> >>>> [   39.555234] pcieport 0000:0c:02.0: bridge window [mem
> >>>> 0x10b00000-0x10bfffff 64bit pref]: failed to add optional 100000
> >>>> [   39.555236] pci 0000:0d:00.0: BAR 4 [mem 0x10b00000-0x10b03fff 64bit
> >>>> pref]: assigned
> >>>> [   39.555290] pci 0000:0d:00.0: BAR 1 [mem 0x10a00000-0x10a00fff]: assigned
> >>>> [   39.555305] pcieport 0000:0c:02.0: PCI bridge to [bus 0d]
> >>>> [   39.556804] pcieport 0000:0c:02.0:   bridge window [mem
> >>>> 0x10a00000-0x10afffff]
> >>>> [   39.557730] pcieport 0000:0c:02.0:   bridge window [mem
> >>>> 0x10b00000-0x10bfffff 64bit pref]
> >>>> [   39.559629] PCI: No. 2 try to assign unassigned res
> >>>> [   39.559636] pcieport 0000:0c:02.0: bridge window [io  size 0x1000]:
> >>>> can't assign; no space
> >>>> [   39.559638] pcieport 0000:0c:02.0: bridge window [io  size 0x1000]:
> >>>> failed to assign
> >>>> [   39.559640] pcieport 0000:0c:02.0: bridge window [io  size 0x1000]:
> >>>> can't assign; no space
> >>>> [   39.559642] pcieport 0000:0c:02.0: bridge window [io  size 0x1000]:
> >>>> failed to assign
> >>>> [   39.559644] pcieport 0000:0c:02.0: PCI bridge to [bus 0d]
> >>>> [   39.561078] pcieport 0000:0c:02.0:   bridge window [mem
> >>>> 0x10a00000-0x10afffff]
> >>>> [   39.562011] pcieport 0000:0c:02.0:   bridge window [mem
> >>>> 0x10b00000-0x10bfffff 64bit pref]
> >>>> [   39.564500] ACPI: \_SB_.L0A2: Enabled at IRQ 37
> >>>> [   39.564541] virtio-pci 0000:0d:00.0: enabling device (0000 -> 0002)
> >>>> [   39.572231] virtio_net virtio2 enp13s0: renamed from eth0
> >>>>
> >>>> Any clue?
> >>>>
> >>>> Thank you in advance
> >>>>
> >>>> Eric
> >>>>
> >>>>
> >>>>
> >>>>
> >>>>
> >>>>
> >>>>
> >>>>>
> >>>>> Additional motivation for this are the upcoming changes that add
> >>>>> complexity to the optional sizing logic due to Resizable BAR awareness.
> >>>>> The extra logic would exceed any reasonable indentation level if the
> >>>>> optional sizing code is kept within the loop body.
> >>>>>
> >>>>> Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
> >>>>> ---
> >>>>>  drivers/pci/setup-bus.c | 77 +++++++++++++++++++++++++++++------------
> >>>>>  1 file changed, 54 insertions(+), 23 deletions(-)
> >>>>>
> >>>>> diff --git a/drivers/pci/setup-bus.c b/drivers/pci/setup-bus.c
> >>>>> index 3d1d3cefcdba..3fcc7641c374 100644
> >>>>> --- a/drivers/pci/setup-bus.c
> >>>>> +++ b/drivers/pci/setup-bus.c
> >>>>> @@ -125,15 +125,6 @@ static resource_size_t get_res_add_size(struct list_head *head,
> >>>>>  	return dev_res ? dev_res->add_size : 0;
> >>>>>  }
> >>>>>  
> >>>>> -static resource_size_t get_res_add_align(struct list_head *head,
> >>>>> -					 struct resource *res)
> >>>>> -{
> >>>>> -	struct pci_dev_resource *dev_res;
> >>>>> -
> >>>>> -	dev_res = res_to_dev_res(head, res);
> >>>>> -	return dev_res ? dev_res->min_align : 0;
> >>>>> -}
> >>>>> -
> >>>>>  static void restore_dev_resource(struct pci_dev_resource *dev_res)
> >>>>>  {
> >>>>>  	struct resource *res = dev_res->res;
> >>>>> @@ -386,6 +377,8 @@ bool pci_resource_is_optional(const struct pci_dev *dev, int resno)
> >>>>>  		return true;
> >>>>>  	if (resno == PCI_ROM_RESOURCE && !(res->flags & IORESOURCE_ROM_ENABLE))
> >>>>>  		return true;
> >>>>> +	if (pci_resource_is_bridge_win(resno) && !resource_size(res))
> >> adding
> >>
> >> && !dev->is_hotplug_bridge makes the hotplug successful.
> >>
> >>
> >> My understanding is that otherwise the hotplug bridge window is
> >> considered as optional and no memoy window is allocated to assign chid
> >> device's BARS
> >>
> >> Please let me know if that makes sense. In the positive I can send a patch.
> > 
> > I don't think that is the correct solution.
> > 
> > 
> > These bridges, have both non-prefetchable and prefetchable windows, but 
> > the initial setup only sets the non-prefetchable one to 2M (and nothing 
> > more would fit to the associated root bus resource). There's only a single 
> > root bus resource that is 2M + a bit more (to fit that BAR0).
> > 
> > Now, when sizing the bridge windows, the kernel sizing algorithm just uses 
> > the default 2M hotplug reservation to both of those windows as there are 
> > not yet any real devices underneath (the default hp reservation is 
> > controllable with hpmmiosize/hpmmioprefsize/hpmemsize cmdline parameters). 
> > Thus, to fit everything, the root bus resource should be 4M + a bit more 
> > for BAR0.
> > 
> > However, it looks to me there's also a 4M add_size miscalculation (the 
> > downstream bridge window is only 2M per each type):
> > 
> > [    0.048078] pci 0000:0a:00.0: bridge window [mem 0x00100000-0x000fffff 64bit pref] to [bus 0b-0d] add_size 400000 add_align 100000
> > [    0.048079] pci 0000:0a:00.0: bridge window [mem 0x00100000-0x000fffff] to [bus 0b-0d] add_size 400000 add_align 100000
> 
> Hum even with the patch below I still get:
> 
> [    0.047253] pci 0000:0a:00.0: bridge window [mem
> 0x00100000-0x000fffff 64bit pref] to [bus 0b-0d] add_size 400000
> add_align 100000
> [    0.047254] pci 0000:0a:00.0: bridge window [mem
> 0x00100000-0x000fffff] to [bus 0b-0d] add_size 400000 add_align 100000

Okay, I'll then have to do a debug patch to know what the loop adds into 
it. I'll try to get it done today.

Thanks anyway for testing.

-- 
 i.

> > It's almost as if both of the child windows would be summed into it, not 
> > just the one with the correct type. Maybe this is caused by the 
> > pci_is_root_bus() thing in pbus_select_window_for_type() (which I don't 
> > like but cannot currently really get rid of either) and 
> > find_bus_resource_of_type() messing things up.
> > 
> > There's an attempt in the patch below to address that problem.
> > 
> > 
> > But, even if the sizing would calculate 2M there, 2M + 2M windows are not 
> > going to fit. This works what looks like by chance in the older kernel, 
> > which (illogically) picks 1M required size for the both window (probably 
> > that comes from min alignment) which magically just happens to fit to the 
> > ~2M root bus resource.
> > 
> > So to solve that issue, you could try with hpmemsize=1M on the kernel's 
> > cmndline to see if it elimnates those failures together with the patch 
> > below.
> Unfortunately it doens't (combination of this fix + hpmemsize=1M)
> > 
> > Why the system setup doesn't create large enough root bus resource for it 
> > is way beyond my qemu and/or aarch64 knowledge and it seems to be where 
> > the problem kind of originates from.
> 
> OK I need more time to investigate. I will come back to you.
> 
> Thanks
> 
> Eric
> > 
> > 
> > --
> > [PATCH 1/1] PCI: Fix mem resource type matching
> > 
> > pbus_select_window_for_type() handles root bus differently by calling
> > find_bus_resource_of_type() with different sets of flags to handle
> > memory window type fallbacks.
> > 
> > The first case is intended to match only exactly, but if type is
> > IORESOURCE_MEM, the check in find_bus_resource_of_type() will not
> > include IORESOURCE_MEM_64 in the mask. As a result, wrong resource
> > may be selected even if a more precise match is available.
> > 
> > Similarly for the other case with IORESOURCE_PREFETCH.
> > 
> > Separate mask handling from the type of the particular resource to
> > ensure the matching progresses from finer-grained matches towards more
> > allowing matches.
> > 
> > Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
> > ---
> >  drivers/pci/setup-bus.c | 10 +++++++---
> >  1 file changed, 7 insertions(+), 3 deletions(-)
> > 
> > diff --git a/drivers/pci/setup-bus.c b/drivers/pci/setup-bus.c
> > index c0a949f2c995..912a30211505 100644
> > --- a/drivers/pci/setup-bus.c
> > +++ b/drivers/pci/setup-bus.c
> > @@ -209,17 +209,21 @@ static struct resource *pbus_select_window_for_type(struct pci_bus *bus,
> >  		return NULL;
> >  
> >  	if (pci_is_root_bus(bus)) {
> > -		win = find_bus_resource_of_type(bus, type, type);
> > +		unsigned long mask = PCI_RES_TYPE_MASK;
> > +
> > +		win = find_bus_resource_of_type(bus, mask, type);
> >  		if (win)
> >  			return win;
> >  
> >  		type &= ~IORESOURCE_MEM_64;
> > -		win = find_bus_resource_of_type(bus, type, type);
> > +		mask &= ~IORESOURCE_MEM_64;
> > +		win = find_bus_resource_of_type(bus, mask, type);
> >  		if (win)
> >  			return win;
> >  
> >  		type &= ~IORESOURCE_PREFETCH;
> > -		return find_bus_resource_of_type(bus, type, type);
> > +		mask &= ~IORESOURCE_PREFETCH;
> > +		return find_bus_resource_of_type(bus, mask, type);
> >  	}
> >  
> >  	switch (iores_type) {
> > 
> > base-commit: dc59e4fea9d83f03bad6bddf3fa2e52491777482
>