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

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 14.11.14 at 16:32, <konrad.wilk@xxxxxxxxxx> 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?
And for the LIST_POISON* override one?

Jan


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