Re: [edk2-devel] [PATCH 2/2] OvmfPkg: Fix PciHostBridgeLibScan

["Ard Biesheuvel" <ardb@kernel.org>]

On Wed, 30 Mar 2022 at 20:29, Sean Rhodes <sean@starlabs.systems> wrote:
>
> From: Patrick Rudolph <patrick.rudolph@9elements.com>
>
> Don't assume a 64bit register always holds an address greater than 4GB.
> Check the value in the register and decide which Aperature it should be
> assigned to.
>
> The same code caused an issue on real hardware. It's unclear if this is an
> issue here as well, as it's intended to run on emulated hardware only.
>

Do you have a link to such a supported issue? Or could you elaborate?
Does it have to do with running out of 64-bit BAR space for resource
that could be located in a 32-bit region as well?


> Cc: Ard Biesheuvel <ardb+tianocore@kernel.org>
> Cc: Jiewen Yao <jiewen.yao@intel.com>
> Cc: Jordan Justen <jordan.l.justen@intel.com>
> Cc: Gerd Hoffmann <kraxel@redhat.com>
> Signed-off-by: Patrick Rudolph <patrick.rudolph@9elements.com>
> ---
>  .../PciHostBridgeLibScan/ScanForRootBridges.c        | 12 ++++++++----
>  1 file changed, 8 insertions(+), 4 deletions(-)
>
> diff --git a/OvmfPkg/Library/PciHostBridgeLibScan/ScanForRootBridges.c b/OvmfPkg/Library/PciHostBridgeLibScan/ScanForRootBridges.c
> index 5fb02a89b9..1ff96be57f 100644
> --- a/OvmfPkg/Library/PciHostBridgeLibScan/ScanForRootBridges.c
> +++ b/OvmfPkg/Library/PciHostBridgeLibScan/ScanForRootBridges.c
> @@ -331,14 +331,18 @@ ScanForRootBridges (
>            Base  = ((UINT32)Pci.Bridge.PrefetchableMemoryBase & 0xfff0) << 16;
>            Limit = (((UINT32)Pci.Bridge.PrefetchableMemoryLimit & 0xfff0)
>                     << 16) | 0xfffff;
> -          MemAperture = &Mem;
>            if (Value == BIT0) {
> -            Base       |= LShiftU64 (Pci.Bridge.PrefetchableBaseUpper32, 32);
> -            Limit      |= LShiftU64 (Pci.Bridge.PrefetchableLimitUpper32, 32);
> -            MemAperture = &MemAbove4G;
> +            Base  |= LShiftU64 (Pci.Bridge.PrefetchableBaseUpper32, 32);
> +            Limit |= LShiftU64 (Pci.Bridge.PrefetchableLimitUpper32, 32);
>            }
>
>            if (Base < Limit) {
> +            if (Base < BASE_4GB) {
> +              MemAperture = &Mem;
> +            } else {
> +              MemAperture = &MemAbove4G;
> +            }
> +
>              if (MemAperture->Base > Base) {
>                MemAperture->Base = Base;
>              }
> --
> 2.32.0
>
>
>
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