Re: [edk2-devel] [PATCH v1 1/1] NetworkPkg/SnpDxe: Register SnpNotifyExitBootServices at TPL_CALLBACK

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

On 04/15/20 18:25, Laszlo Ersek wrote:

> In other words, I personally believe that bug#1974 should have been
> closed as INVALID (without patching the edk2 source). The EBS handler in
> SnpDxe is necessary (as long as it does not alter the UEFI memory map
> itself), because sending the Shutdown CDB at EBS *is* needed, and the
> UNDI-providing agent that processes the Shutdown CDB *cannot* release
> UEFI-owned memory.

For the patch that's being proposed in this thread:

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

However, there *is* a bug in SnpNotifyExitBootServices(). Namely, it
calls PxeShutdown(), and PxeShutdown() does two things:

(a) it sends the Shutdown CDB,
(b) it calls Snp->PciIo->FreeBuffer().

Step (a) is required in the EBS handler context.

Step (b) is *forbidden* in the EBS handler context.

Therefore, the cut must be made *between* steps (a) and (b).

PxeShutdown() is alright to call from SimpleNetworkDriverStop(), but it
is *not* fit for an EBS handler.

(SnpNotifyExitBootServices() also calls PxeStop(). I'm not sure if that
is really necessary, but at least PxeStop() only sends a CDB to UNDI,
and manipulates "Snp->Mode.State". Those actions do not interfere with
the UEFI memmap, so they are harmless in this aspect.)

"in my opinion", as always :)

Thanks,
Laszlo