Re: [PATCH] RFC Inform UEFI memory to Linux

[Ard Biesheuvel <ard.biesheuvel@linaro.org>]

On 17 September 2017 at 21:07, Udit Kumar <udit.kumar@nxp.com> wrote:
> Hi Ard,
>
>> Thanks for the patch. But please consider carefully what you're doing:
>> My point is really that you can just remove lines 124 - 189 instead.
>
> We want, OS to re-use firmware volume area.  Therefore making firmware volume visible.
> You are right, removing lines  124-189 will do the same, and no need of adding splitting area with same
> attribute.
>
> Also, I am not sure, if we can remove this entirely, therefore we posted this as RFC:)
> Code comments says
>
>  // EDK2 does not have the concept of boot firmware copied into DRAM. To avoid the DXE
>  // core to overwrite this area we must mark the region with the attribute non-present
>
> On our architecture, we start boot from DRAM. And we haven't seen any overwrite
> by DXE. This work perfectly well for us.
>
> Do you think, on other platforms it may add a risk of overwrite ?
>

We wondered about that as well. As far as I can tell, a compressed FV
will be decompressed completely into a memory region that is reserved
for it before the DXE core is invoked. This means the outer,
uncompressed FV could technically be overwritten, but in practice, we
never refer back to it in a PrePi build, and we should probably not
even build the FV hob for this volume if we can avoid it.