*** Description of problem:

(This issue was found as part of
<https://bugzilla.redhat.com/show_bug.cgi?id=1437113#c13>.)

The PciBusDxe driver in OVMF currently aligns the length of the total
resource demand a given resource type) of a bridge to the max BAR alignment
required by any device behind the bridge. This is incorrect -- while BARs
behind the bridge are sorted in decreasing size & alignment order, so that
all their base addresses are correctly aligned, their accumulated size need
not and should not be aligned (rounded up) at all.

Consider an example where device #1 needs an MMIO BAR of 16MB size, and
device #2 needs an MMIO BAR of 8MB size. This means device #1's BAR will
come first (at an address aligned at 16MB, and ending at a similarly aligned
address), and device #2's BAR will come second (at the previous end-address,
aligned at 16MB, which satisfies the 8MB alignment requirement; and ending
at an address aligned at 8MB). From the base of device #1's BAR, the
bridge's own base alignment will be 16MB. However, the size of the bridge's
resource demand should be 16MB + 8MB = 24MB, not 32MB (i.e., 24MB rounded up
to a multiple of 16MB).

*** Version-Release number of selected component (if applicable):

OVMF-20171011-1.git92d07e48907f.el7.noarch

(For the reproducer below, you also need a qemu-kvm-rhev package that fixes
bug 1437113.)

*** How reproducible:

100%

*** Steps to Reproduce:

(Instead of multiple devices behind a bridge, this reproducer uses multiple
paddings (resource reservations) for a single PCI Express root port. The
symptoms are exhibited the same way.)

CODE=/usr/share/OVMF/OVMF_CODE.secboot.verbose.fd
TMPL=/usr/share/OVMF/OVMF_VARS.fd
UEFI_SHELL=/usr/share/OVMF/UefiShell.verbose.iso
QEMU=/usr/libexec/qemu-kvm

cp $TMPL vars.overclaim.fd

$QEMU \
  -nodefconfig \
  -nodefaults \
  \
  -m 1024 \
  \
  -machine q35,smm=on,accel=kvm \
  -global driver=cfi.pflash01,property=secure,value=on \
  \
  -drive if=pflash,readonly,format=raw,file=$CODE \
  -drive if=pflash,format=raw,file=vars.overclaim.fd \
  \
  -chardev file,id=debugfile,path=debug.overclaim.log \
  -device isa-debugcon,iobase=0x402,chardev=debugfile \
  \
  -chardev stdio,signal=off,mux=on,id=char0 \
  -mon chardev=char0,mode=readline \
  -serial chardev:char0 \
  \
  -device pcie-root-port,id=rp1,bus=pcie.0,multifunction=on,addr=1.0,chassis=1 \
  -device pcie-root-port,id=rp2,bus=pcie.0,multifunction=on,addr=1.1,chassis=2 \
  -device pcie-root-port,id=rp3,bus=pcie.0,multifunction=on,addr=1.2,chassis=3,io-reserve=4K,mem-reserve=8M,pref32-reserve=16M \
  \
  -device virtio-gpu-pci,bus=rp1 \
  \
  -device qemu-xhci,id=xhci,bus=rp2 \
  -device usb-tablet,bus=xhci.0 \
  \
  -device virtio-rng-pci,bus=rp3,disable-legacy=on,disable-modern=off \
  \
  -device virtio-scsi-pci,id=scsi0,bus=pcie.0,addr=2.0 \
  -device scsi-cd,bus=scsi0.0,drive=uefi-shell,bootindex=0 \
  -drive if=none,format=raw,file=$UEFI_SHELL,id=uefi-shell,readonly

*** Actual results:

The "debug.overclaim.log" file will contain:

> PciBus: Resource Map for Bridge [00|01|02]
> Type =   Io16; Base = 0x6000;   Length = 0x1000;        Alignment = 0xFFF
>    Base = Padding;      Length = 0x1000;        Alignment = 0xFFF
> Type =  Mem32; Base = 0x90000000;       Length = 0x2000000;     Alignment = 0xFFFFFF
                                          ^^^^^^^^^^^^^^^^^^
>    Base = Padding;      Length = 0x1000000;     Alignment = 0xFFFFFF
>    Base = Padding;      Length = 0x800000;      Alignment = 0x7FFFFF
> Type =  Mem32; Base = 0x92402000;       Length = 0x1000;        Alignment = 0xFFF
> Type = PMem64; Base = 0x800100000;      Length = 0x100000;      Alignment = 0xFFFFF
>    Base = 0x800100000;  Length = 0x4000;        Alignment = 0x3FFF;     Owner = PCI [03|00|00:20]

*** Expected results:

The "debug.overclaim.log" file should contain:

> PciBus: Resource Map for Bridge [00|01|02]
> Type =   Io16; Base = 0x6000;   Length = 0x1000;        Alignment = 0xFFF
>    Base = Padding;      Length = 0x1000;        Alignment = 0xFFF
> Type =  Mem32; Base = 0x90000000;       Length = 0x1800000;     Alignment = 0xFFFFFF
                                          ^^^^^^^^^^^^^^^^^^
>    Base = Padding;      Length = 0x1000000;     Alignment = 0xFFFFFF
>    Base = Padding;      Length = 0x800000;      Alignment = 0x7FFFFF
> Type =  Mem32; Base = 0x91C02000;       Length = 0x1000;        Alignment = 0xFFF
> Type = PMem64; Base = 0x800100000;      Length = 0x100000;      Alignment = 0xFFFFF
>    Base = 0x800100000;  Length = 0x4000;        Alignment = 0x3FFF;     Owner = PCI [03|00|00:20]

*** Additional information:

This was fixed in upstream commit 6e3287442774 ("MdeModulePkg/PciBus: Fix
bug that PCI BUS claims too much resource", 2017-10-20).