Re: [Qemu-devel] [edk2] [edk2 PATCH 0/1] OvmfPkg: grab ACPI tables from QEMU

[Laszlo Ersek <lersek@redhat.com>]

On 11/12/13 16:11, Laszlo Ersek wrote:

> - Boot progress bar and console (efifb) continue to work (tested with
>   both 1GB and 5GB guest sizes).

Turns out one can't be diligent enough.

This patch causes (or exposes, dependent on your POV) breakage. It
breaks the cirrus video output for both RHEL-6 and Windows 2012 R2
guests, very early during boot, *if* the guest RAM size is 2560 MB.

(That amount is just an example, but a good example (= an esp. bad value).)

When the guest has this much RAM, then the built-in OVMF algorithm
advertises the following 32-bit PCI window (no 64-bit PCI window) in
\_SB.PCI0._CRS:

  ACPI PciWindow32: Base=0xA0000000 End=0xFEEFFFFF Length=0x5EF00000
  ACPI PciWindow64: Base=0x00000000 End=0x00000000 Length=0x00000000

(inclusive End). That is, the windows starts right above the
conventional memory; 0xA0000000 == 2560M.

However, the ACPI table exported by qemu says

  begin32=c0000000 end32=fec00000 begin64=0 end64=0

(exclusive end32).

Even though this latter range is a proper subset of the former, it
breaks the cirrus display in both said guests (didn't test more guests).

When I applied this PoC patch on qemu, the displays started to work:

diff --git a/hw/pci-host/piix.c b/hw/pci-host/piix.c
index edc974e..305b786 100644
--- a/hw/pci-host/piix.c
+++ b/hw/pci-host/piix.c
@@ -348,11 +348,11 @@ PCIBus *i440fx_init(PCII440FXState **pi440fx_state,
     /* Set PCI window size the way seabios has always done it. */
     /* Power of 2 so bios can cover it with a single MTRR */
     if (ram_size <= 0x80000000) {
         i440fx->pci_info.w32.begin = 0x80000000;
     } else if (ram_size <= 0xc0000000) {
-        i440fx->pci_info.w32.begin = 0xc0000000;
+        i440fx->pci_info.w32.begin = 0xa0000000;
     } else {
         i440fx->pci_info.w32.begin = 0xe0000000;
     }

     memory_region_init_alias(&f->pci_hole, OBJECT(d), "pci-hole",
f->pci_address_space,

I guess the range starting at 0xc0000000 is somehow "incompatible" with
the EFI memory map. (I can't actually explain this idea because, again,
this second range is a proper subset of the former, and its size is
still 1004MB.)

The comment before the w32.begin assignments is interesting. It dates
back to qemu commit 3459a625 ("pci: store PCI hole ranges in guestinfo
structure"). It could be incompatible with the *current* OVMF memory
map, but of course the OVMF memory map could be wrong as well.

I've no idea how to fix this disagreement.

Thanks
Laszlo