Re: [RFC PATCH] efi/libstub: Update memory map after calling priv_func

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> On Aug 1, 2018, at 11:33 AM, Ard Biesheuvel <ard.biesheuvel@xxxxxxxxxx> wrote:
> 
> On 1 August 2018 at 19:07, Jeffrey Hugo <jhugo@xxxxxxxxxxxxxx> wrote:
>> On 8/1/2018 10:27 AM, Eric Snowberg wrote:
>>> Once EBS is called, there isn’t enough room available for the new memory
>>> map on a very large system (do to the memory that was previously allocated
>>> in exit_boot_func).
>>> 
>>> The race condition that exists between priv_func and the call to EBS will
>>> be taken care of by the existing code, thru the slack slots.
>> 
>> 
>> Now I'm slightly confused.  There isn't an issue because of slack slots?
>> 
>> I'm kind of wondering if our assumption that 8 slots would be enough is not
>> invalid, and therefore we need to increase that number.  I hate kicking the
>> can down the road like that, but as discussed in 2016, there doesn't seem to
>> be a good alternative.
>> 
> 
> But why does alloc_e820ext have to be deferred to the last minute?

I didn’t understand that either. If it was done earlier, I assume there would not be a problem. 

Our tests show any kernel prior to Commit d64934019f6c ("x86/efi: Use efi_exit_boot_services()”) will boot successfully.  The first "goto get_map" that was removed from the previous exit_boot insured their was enough room for the memory map when EBS was called.

Which would you rather see done?  Increase the slack number or move the e820 code?  I can look at doing either if you'd like.

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