Re: [edk2-devel] [PATCH v2] ArmVirt: Allow memory attributes protocol to be disabled on first boot

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

On 12/8/23 15:34, Laszlo Ersek wrote:

> (7) Tying back to my point (4) -- I understand this is a hack anyway,
> but I'm still uncomfortable with platform BDS uninstalling a protocol
> that is owned by / provided by the CPU driver. Feels like a significant
> layering violation.
> 
> Can we modify the CPU driver instead, to listen to a new event group,
> upon which being signaled, the CPU driver would uninstall the protocol
> (and close the listening event)?
> 
> This PlatformBootManagerLib instance would act more or less the same
> (I'd suggest signaling the event group from within AfterConsole, in case
> the PCD default and/or the fw_cfg knob dictated that), but the protocol
> uninstallation would occur in "ArmPkg/Drivers/CpuDxe".
> 
> In more technical terms, the layering violation IMO is that we mess with
> CpuDxe's "mCpuHandle" and "mMemoryAttribute" static variables from
> within BDS. Adding the new event group requires more boiler-plate code
> for sure, but there's a small code-size benefit as well: we'd not have
> to look up either the handle (with LocateHandle) or the protocol
> interface (with HandleProtocol), as CpuDxe inherently knows those
> (mCpuHandle, mMemoryAttribute).

Or maybe avoid modifying PlatformBootManagerLib completely; instead,
move the logic into CpuDxe, into a ready-to-boot event handler?

At that time, variable services should be available to CpuDxe as well
(for the BootOrder UEFI var check).

Laszlo



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