Re: [PATCH RFC] EFI: allow retry of ExitBootServices() call

[Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>]

On Mon, Nov 17, 2014 at 01:35:17PM +0000, Jan Beulich wrote:
> >>> On 14.11.14 at 16:32, <konrad.wilk@oracle.com> wrote:
> > On Fri, Nov 14, 2014 at 12:37:30PM +0000, Jan Beulich wrote:
> >> The specification is kind of vague under what conditions
> >> ExitBootServices() may legitimately fail, requiring the OS loader to
> >> retry:
> >> 
> >> "If MapKey value is incorrect, ExitBootServices() returns
> >>  EFI_INVALID_PARAMETER and GetMemoryMap() with ExitBootServices() must
> >>  be called again. Firmware implementation may choose to do a partial
> >>  shutdown of the boot services during the first call to
> >>  ExitBootServices(). EFI OS loader should not make calls to any boot
> >>  service function other then GetMemoryMap() after the first call to
> >>  ExitBootServices()."
> >> 
> >> While our code guarantees the map key to be valid, there are systems
> >> where a firmware internal notification sent while processing
> >> ExitBootServices() reportedly results in changes to the memory map.
> > 
> > s/reportedly/in fact/
> >> In that case, make a best effort second try: Avoid any boot service
> >> calls other than the two named above, with the possible exception of
> >> error paths. Those aren't a problem, since if we end up needing to
> >> retry, we're hosed when something goes wrong as much as if we didn't
> >> make the retry attempt.
> >> 
> >> For x86, a minimal adjustment to efi_arch_process_memory_map() is
> >> needed for it to cope with potentially being called a second time.
> > 
> > Wow. Talk about timing. We saw this and were going to see
> > doing something similar.
> 
> So what are your thoughts then regarding this patch going into 4.5?

Definitly should go in - and I would even say backport to earlier
versions of Xen.

> And for the LIST_POISON* override one?

Yes as well please.
> 
> Jan
>