Re: [Qemu-devel] [PATCH 4/4] i386/acpi-build: build_crs(): fetch BAR from PCI config space directly

["Michael S. Tsirkin" <mst@redhat.com>]

On Sat, Jun 06, 2015 at 01:46:29AM +0200, Laszlo Ersek wrote:
> OVMF downloads the ACPI linker/loader script from QEMU when the edk2 PCI
> Bus driver globally signals the firmware that PCI enumeration and resource
> allocation have completed. At this point QEMU regenerates the ACPI payload
> in an fw_cfg read callback, and this is when the PXB's _CRS gets
> populated.
> 
> Unfortunately, when this happens, the PCI_COMMAND_MEMORY bit is clear in
> the root bus's command register, *unlike* under SeaBIOS. The consequences
> unfold as follows:
> 
> - When build_crs() fetches dev->io_regions[i].addr, it is all-bits-one,
>   because pci_update_mappings() --> pci_bar_address() calculated it as
>   PCI_BAR_UNMAPPED, due to the PCI_COMMAND_MEMORY bit being clear.
> 
> - Consequently, the SHPC MMIO BAR (bar 0) of the bridge is not added to
>   the _CRS, *despite* having been programmed in PCI config space.
> 
> - Similarly, the SHPC MMIO BAR of the PXB is not removed from the main
>   root bus's DWordMemory descriptor.
> 
> - Guest OSes (Linux and Windows alike) notice the pre-programmed SHPC BAR
>   within the PXB's config space, and notice that it conflicts with the
>   main root bus's memory resource descriptors. Linux reports
> 
>   pci 0000:04:00.0: BAR 0: can't assign mem (size 0x100)
>   pci 0000:04:00.0: BAR 0: trying firmware assignment [mem
>                            0x88200000-0x882000ff 64bit]
>   pci 0000:04:00.0: BAR 0: [mem 0x88200000-0x882000ff 64bit] conflicts
>                            with PCI Bus 0000:00 [mem
>                            0x88200000-0xfebfffff]
> 
>   While Windows Server 2012 R2 reports
> 
>     https://technet.microsoft.com/en-us/library/cc732199%28v=ws.10%29.aspx
> 
>     This device cannot find enough free resources that it can use. If you
>     want to use this device, you will need to disable one of the other
>     devices on this system. (Code 12)
> 
> (This issue was apparently encountered earlier, see:
> 
>   https://lists.nongnu.org/archive/html/qemu-devel/2015-01/msg02983.html
> 
> and the current hole-punching logic in build_crs() and build_ssdt() is
> probably supposed to remedy exactly that problem -- however, for OVMF they
> don't work, because at the end of the PCI enumeration and resource
> allocation, which cues the ACPI linker/loader client, the command register
> is clear.)
> 
> The solution is to fetch the BAR addresses from PCI config space directly,
> for the purposes of build_crs(), regardless of the PCI command register
> and any MemoryRegion state.
> 
> Example MMIO maps for a 2GB guest:
> 
> SeaBIOS:
> 
>   main: 0x80000000..0xFC000000 / 0x7C000000
>   pxb:  0xFC000000..0xFC200000 / 0x00200000
>   main: 0xFC200000..0xFC213000 / 0x00013000
>   pxb:  0xFC213000..0xFC213100 / 0x00000100 <- SHPC BAR
>   main: 0xFC213100..0xFEA00000 / 0x027ECF00
>   pxb:  0xFEA00000..0xFEC00000 / 0x00200000
> 
> OVMF, without the fix:
> 
>   main: 0x80000000..0x88100000 / 0x08100000
>   pxb:  0x88100000..0x88200000 / 0x00100000
>   main: 0x88200000..0xFEC00000 / 0x76A00000
> 
> OVMF, with the fix:
> 
>   main: 0x80000000..0x88100000 / 0x08100000
>   pxb:  0x88100000..0x88200000 / 0x00100000
>   pxb:  0x88200000..0x88200100 / 0x00000100 <- SHPC BAR
>   main: 0x88200100..0xFEC00000 / 0x769FFF00
> 
> (Note that under OVMF the PCI enumerator includes requests for
> prefetchable memory in the nonprefetchable memory pool -- separate windows
> for nonprefetchable and prefetchable memory are not supported (yet) --
> that's why there's one fewer pxb range in the corrected OVMF case than in
> the SeaBIOS case.)
> 
> Cc: Marcel Apfelbaum <marcel@redhat.com>
> Cc: Michael S. Tsirkin <mst@redhat.com>
> Signed-off-by: Laszlo Ersek <lersek@redhat.com>

This is problematic - disabled BAR values have no meaning according to
the PCI spec.

It might be best to add a property to just disable shpc in the bridge so
no devices reside directly behind the pxb?

> ---
>  hw/i386/acpi-build.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/hw/i386/acpi-build.c b/hw/i386/acpi-build.c
> index b71e942..60d4f75 100644
> --- a/hw/i386/acpi-build.c
> +++ b/hw/i386/acpi-build.c
> @@ -784,8 +784,8 @@ static Aml *build_crs(PCIHostState *host,
>          for (i = 0; i < PCI_NUM_REGIONS; i++) {
>              PCIIORegion *r = &dev->io_regions[i];
>  
> -            range_base = r->addr;
> -            range_limit = r->addr + r->size - 1;
> +            range_base = pci_bar_address(dev, i, r->type, r->size, false);
> +            range_limit = range_base + r->size - 1;
>  
>              /*
>               * Work-around for old bioses
> -- 
> 1.8.3.1