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

From: Eric Auger

Date: Tue Jul 07 2026 - 11:54:26 EST

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

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@xxxxxxxxxxxxxxx>
> ---
> 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))
> + return true;
>
> return false;
> }
> @@ -1258,6 +1251,54 @@ static resource_size_t calculate_head_align(resource_size_t *aligns,
> return head_align;
> }
>
> +/*
> + * pbus_size_mem_optional - Account optional resources in bridge window
> + *
> + * Account an optional resource or the optional part of the resource in bridge
> + * window size.
> + *
> + * Return: %true if the resource is entirely optional.
> + */
> +static bool pbus_size_mem_optional(struct pci_dev *dev, int resno,
> + resource_size_t align,
> + struct list_head *realloc_head,
> + resource_size_t *add_align,
> + resource_size_t *children_add_size)
> +{
> + struct resource *res = pci_resource_n(dev, resno);
> + bool optional = pci_resource_is_optional(dev, resno);
> + resource_size_t r_size = resource_size(res);
> + struct pci_dev_resource *dev_res;
> +
> + if (!realloc_head)
> + return false;
> +
> + if (!optional) {
> + /*
> + * Only bridges have optional sizes in realloc_head at this
> + * point. As res_to_dev_res() walks the entire realloc_head
> + * list, skip calling it when known unnecessary.
> + */
> + if (!pci_resource_is_bridge_win(resno))
> + return false;
> +
> + dev_res = res_to_dev_res(realloc_head, res);
> + if (dev_res) {
> + *children_add_size += dev_res->add_size;
> + *add_align = max(*add_align, dev_res->min_align);
> + }
> +
> + return false;
> + }
> +
> + /* Put SRIOV requested res to the optional list */
> + add_to_list(realloc_head, dev, res, 0, align);
> + *children_add_size += r_size;
> + *add_align = max(align, *add_align);
> +
> + return true;
> +}
> +
> /**
> * pbus_size_mem() - Size the memory window of a given bus
> *
> @@ -1284,7 +1325,6 @@ static void pbus_size_mem(struct pci_bus *bus, struct resource *b_res,
> resource_size_t aligns[28] = {}; /* Alignments from 1MB to 128TB */
> int order, max_order;
> resource_size_t children_add_size = 0;
> - resource_size_t children_add_align = 0;
> resource_size_t add_align = 0;
>
> if (!b_res)
> @@ -1311,7 +1351,6 @@ static void pbus_size_mem(struct pci_bus *bus, struct resource *b_res,
> if (b_res != pbus_select_window(bus, r))
> continue;
>
> - r_size = resource_size(r);
> align = pci_resource_alignment(dev, r);
> /*
> * aligns[0] is for 1MB (since bridge memory
> @@ -1327,25 +1366,17 @@ static void pbus_size_mem(struct pci_bus *bus, struct resource *b_res,
> continue;
> }
>
> - /* Put SRIOV requested res to the optional list */
> - if (realloc_head && pci_resource_is_optional(dev, i)) {
> - add_align = max(align, add_align);
> - add_to_list(realloc_head, dev, r, 0, 0 /* Don't care */);
> - children_add_size += r_size;
> + if (pbus_size_mem_optional(dev, i, align,
> + realloc_head, &add_align,
> + &children_add_size))
> continue;
> - }
>
> + r_size = resource_size(r);
> size += max(r_size, align);
>
> aligns[order] += align;
> if (order > max_order)
> max_order = order;
> -
> - if (realloc_head) {
> - children_add_size += get_res_add_size(realloc_head, r);
> - children_add_align = get_res_add_align(realloc_head, r);
> - add_align = max(add_align, children_add_align);
> - }
> }
> }
>