Re: [edk2-devel] [PATCH v6 09/11] OvmfPkg/PciHostBridgeUtilityLib: Extend GetRootBridges() with BusMin/BusMax

["Laszlo Ersek" <lersek@redhat.com>]

On 01/19/21 02:13, Jiahui Cen via groups.io wrote:
> Extend parameter list of PciHostBridgeUtilityGetRootBridges() with BusMin/
> BusMax, so that the utility function could be compatible with ArmVirtPkg
> who uses mutable bus range [BusMin, BusMax] insteand of [0, PCI_MAX_BUS].
> 
> BZ: https://bugzilla.tianocore.org/show_bug.cgi?id=3059
> 
> Cc: Jordan Justen <jordan.l.justen@intel.com>
> Cc: Laszlo Ersek <lersek@redhat.com>
> Cc: Ard Biesheuvel <ard.biesheuvel@arm.com>
> Signed-off-by: Jiahui Cen <cenjiahui@huawei.com>
> ---
>  OvmfPkg/Include/Library/PciHostBridgeUtilityLib.h                 |  6 ++++
>  OvmfPkg/Library/PciHostBridgeLib/PciHostBridgeLib.c               |  2 ++
>  OvmfPkg/Library/PciHostBridgeUtilityLib/PciHostBridgeUtilityLib.c | 30 ++++++++++++++++----
>  3 files changed, 33 insertions(+), 5 deletions(-)
> 
> diff --git a/OvmfPkg/Include/Library/PciHostBridgeUtilityLib.h b/OvmfPkg/Include/Library/PciHostBridgeUtilityLib.h
> index a0ea44d96a67..d2dc18a1afad 100644
> --- a/OvmfPkg/Include/Library/PciHostBridgeUtilityLib.h
> +++ b/OvmfPkg/Include/Library/PciHostBridgeUtilityLib.h
> @@ -112,6 +112,10 @@ PciHostBridgeUtilityUninitRootBridge (
>  
>    @param[in]  NoExtendedConfigSpace  No Extended Config Space.
>  
> +  @param[in]  BusMin                 Minimum Bus number, inclusive.
> +
> +  @param[in]  BusMax                 Maximum Bus number, inclusive.
> +
>    @param[in]  Io                     IO aperture.
>  
>    @param[in]  Mem                    MMIO aperture.
> @@ -132,6 +136,8 @@ PciHostBridgeUtilityGetRootBridges (
>    IN  UINT64                   AllocationAttributes,
>    IN  BOOLEAN                  DmaAbove4G,
>    IN  BOOLEAN                  NoExtendedConfigSpace,
> +  IN  UINTN                    BusMin,
> +  IN  UINTN                    BusMax,
>    IN  PCI_ROOT_BRIDGE_APERTURE *Io,
>    IN  PCI_ROOT_BRIDGE_APERTURE *Mem,
>    IN  PCI_ROOT_BRIDGE_APERTURE *MemAbove4G,
> diff --git a/OvmfPkg/Library/PciHostBridgeLib/PciHostBridgeLib.c b/OvmfPkg/Library/PciHostBridgeLib/PciHostBridgeLib.c
> index 91b9e6baa1e8..7d9fb0fb293a 100644
> --- a/OvmfPkg/Library/PciHostBridgeLib/PciHostBridgeLib.c
> +++ b/OvmfPkg/Library/PciHostBridgeLib/PciHostBridgeLib.c
> @@ -85,6 +85,8 @@ PciHostBridgeGetRootBridges (
>      AllocationAttributes,
>      FALSE,
>      PcdGet16 (PcdOvmfHostBridgePciDevId) != INTEL_Q35_MCH_DEVICE_ID,
> +    0,
> +    PCI_MAX_BUS,
>      &Io,
>      &Mem,
>      &MemAbove4G,
> diff --git a/OvmfPkg/Library/PciHostBridgeUtilityLib/PciHostBridgeUtilityLib.c b/OvmfPkg/Library/PciHostBridgeUtilityLib/PciHostBridgeUtilityLib.c
> index 1d78984b83ad..69bed5c7843f 100644
> --- a/OvmfPkg/Library/PciHostBridgeUtilityLib/PciHostBridgeUtilityLib.c
> +++ b/OvmfPkg/Library/PciHostBridgeUtilityLib/PciHostBridgeUtilityLib.c
> @@ -200,6 +200,10 @@ PciHostBridgeUtilityUninitRootBridge (
>  
>    @param[in]  NoExtendedConfigSpace  No Extended Config Space.
>  
> +  @param[in]  BusMin                 Minimum Bus number, inclusive.
> +
> +  @param[in]  BusMax                 Maximum Bus number, inclusive.
> +
>    @param[in]  Io                     IO aperture.
>  
>    @param[in]  Mem                    MMIO aperture.
> @@ -220,6 +224,8 @@ PciHostBridgeUtilityGetRootBridges (
>    IN  UINT64                   AllocationAttributes,
>    IN  BOOLEAN                  DmaAbove4G,
>    IN  BOOLEAN                  NoExtendedConfigSpace,
> +  IN  UINTN                    BusMin,
> +  IN  UINTN                    BusMax,
>    IN  PCI_ROOT_BRIDGE_APERTURE *Io,
>    IN  PCI_ROOT_BRIDGE_APERTURE *Mem,
>    IN  PCI_ROOT_BRIDGE_APERTURE *MemAbove4G,
> @@ -236,6 +242,13 @@ PciHostBridgeUtilityGetRootBridges (
>    UINTN                LastRootBridgeNumber;
>    UINTN                RootBridgeNumber;
>  
> +  if (BusMin > BusMax || BusMax > PCI_MAX_BUS) {
> +    DEBUG ((DEBUG_ERROR, "%a: invalid bus range with BusMin %d and BusMax %d\n",
> +      __FUNCTION__, BusMin, BusMax));

(1) The "%d" format specifier is appropriate for INT32 values. But UINTN
is either UINT32 or UINT64 (dependent on the edk2 architecture the
platform is built for).

The safe way to print a UINTN value is to (a) cast it to UINT64, and (b)
use the "%Lu" (or "%Lx") format specifier.

I'll fix this up for you.

> +    *Count = 0;

(2) As I said under patch v6 07/11, this zeroing should be centralized
at the top of the function. I'll fix it up for you.

> +    return NULL;
> +  }
> +
>    //
>    // QEMU provides the number of extra root buses, shortening the exhaustive
>    // search below. If there is no hint, the feature is missing.
> @@ -247,7 +260,14 @@ PciHostBridgeUtilityGetRootBridges (
>      QemuFwCfgSelectItem (FwCfgItem);
>      QemuFwCfgReadBytes (FwCfgSize, &ExtraRootBridges);
>  
> -    if (ExtraRootBridges > PCI_MAX_BUS) {
> +    //
> +    // Validate the number of extra root bridges. As BusMax is inclusive, the
> +    // max bus count is (BusMax - BusMin + 1). From that, the "main" root bus
> +    // is always givin, so the max count for the "extra" root bridges is one

(3) s/givin/a given/

I'll fix it.

> +    // less, i.e. (BusMax - BusMin). If QEME hint exceeds that, we have invalid

(4) s/QEME/the QEMU/

I'll fix it.

> +    // behavior.
> +    //
> +    if (ExtraRootBridges > BusMax - BusMin) {
>        DEBUG ((DEBUG_ERROR, "%a: invalid count of extra root buses (%Lu) "
>          "reported by QEMU\n", __FUNCTION__, ExtraRootBridges));
>        *Count = 0;
> @@ -271,15 +291,15 @@ PciHostBridgeUtilityGetRootBridges (
>    //
>    // The "main" root bus is always there.
>    //
> -  LastRootBridgeNumber = 0;
> +  LastRootBridgeNumber = BusMin;

Side remark (nothing to fix): I'm slightly curious what would happen if
the DTB on the arm/aarch64 "virt" machine reported a BusMin different
from 0. What does that mean for the MMCONFIG offsets? If BusMin is
nonzero, does that mean we have a unused slice at the start of MMCONFIG?
Or does it mean that we need to shift down the bus references so that
BusMin does map to offset 0 in MMCONFIG? (See also the
"PCI_ROOT_BRIDGE.Bus.Translation" field.)

Anyway, we can look at this later, if such a DTB ever occurs in
practice. (I doubt that it ever will.)


>  
>    //
>    // Scan all other root buses. If function 0 of any device on a bus returns a
>    // VendorId register value different from all-bits-one, then that bus is
>    // alive.
>    //
> -  for (RootBridgeNumber = 1;
> -       RootBridgeNumber <= PCI_MAX_BUS && Initialized < ExtraRootBridges;
> +  for (RootBridgeNumber = BusMin + 1;
> +       RootBridgeNumber <= BusMax && Initialized < ExtraRootBridges;
>         ++RootBridgeNumber) {
>      UINTN Device;
>  
> @@ -329,7 +349,7 @@ PciHostBridgeUtilityGetRootBridges (
>      DmaAbove4G,
>      NoExtendedConfigSpace,
>      (UINT8) LastRootBridgeNumber,
> -    PCI_MAX_BUS,
> +    (UINT8) BusMax,
>      Io,
>      Mem,
>      MemAbove4G,
> 

Reviewed-by: Laszlo Ersek <lersek@redhat.com>

Thanks
Laszlo