Re: [edk2] [PATCH] OvmfPkg: prevent 64-bit MMIO BAR degradation if there is no CSM

["David Woodhouse" <dwmw2@infradead.org>]

[-- Attachment #1: Type: text/plain, Size: 2529 bytes --]

On Thu, 2016-05-19 at 00:12 +0200, Laszlo Ersek wrote:
> According to edk2 commit
> 
>   "MdeModulePkg/PciBus: do not improperly degrade resource"
> 
> and to the EFI_INCOMPATIBLE_PCI_DEVICE_SUPPORT_PROTOCOL definition in the
> Platform Init 1.4a specification, a platform can provide such a protocol
> in order to influence the PCI resource allocation performed by the PCI Bus
> driver.
> 
> In particular it is possible instruct the PCI Bus driver, with a
> "wildcard" hint, to allocate the 64-bit MMIO BARs of a device in 64-bit
> address space, regardless of whether the device features an option ROM.
> 
> (By default, the PCI Bus driver considers an option ROM reason enough for
> allocating the 64-bit MMIO BARs in 32-bit address space. It cannot know if
> BDS will launch a legacy boot option, and under legacy boot, a legacy BIOS
> binary from a combined option ROM could be dispatched, and fail to access
> MMIO BARs in 64-bit address space.)
> 
> In platform code we can ascertain whether a CSM is present or not. If not,
> then legacy BIOS binaries in option ROMs can't be dispatched, hence the
> BAR degradation is detrimental, and we should prevent it. This is expected
> to conserve the 32-bit address space for 32-bit MMIO BARs.
> 
> The driver added in this patch could be simplified based on the following
> facts:
> 
> - In the Ia32 build, the 64-bit MMIO aperture is always zero-size, hence
>   the driver will exit immediately. Therefore the driver could be omitted
>   from the Ia32 build.
> 
> - In the Ia32X64 and X64 builds, the driver could be omitted if CSM_ENABLE
>   was defined (because in that case the degradation would be justified).
>   On the other hand, if CSM_ENABLE was undefined, then the driver could be
>   included, and it could provide the hint unconditionally (without looking
>   for the Legacy BIOS protocol).
> 
> These short-cuts are not taken because they would increase the differences
> between the OVMF DSC/FDF files. If we can manage without extreme
> complexity, we should use dynamic logic (vs. build time configuration),
> plus keep conditional compilation to a minimum.
> 
> Cc: Jordan Justen <jordan.l.justen@intel.com>
> Cc: Ruiyu Ni <ruiyu.ni@intel.com>
> Contributed-under: TianoCore Contribution Agreement 1.0
> Signed-off-by: Laszlo Ersek <lersek@redhat.com>

This (commit 855743f717745) appears not to be working any more. I see
NVMe controllers' BARs being assigned above 4GiB where the CSM can't
reach them.



[-- Attachment #2: smime.p7s --]
[-- Type: application/x-pkcs7-signature, Size: 5174 bytes --]