Re: smm lock query

[Andrew Fish <afish@apple.com>]

> On May 27, 2018, at 1:44 PM, Andrew Fish <afish@apple.com> wrote:
> 
> 
> 
>> On May 27, 2018, at 9:47 AM, Marvin H?user <Marvin.Haeuser@outlook.com> wrote:
>> 
>> Good day Abhishek,
>> 
>> I CC'd the MdeModulePkg maintainers, Ruiyu for the Platform BDS aspect (exposes the ReadyToLock protocol) and Laszlo for his high-quality answers.
>> 
>> Strictly speaking you are, right, because of the description for the MM protocol:
>> "Indicates that MM resources and services that should not be used by the third party code are about[Marvin: (!)] to be locked."
>> Practically however, I don't see any issue with the current implementation. Code inside MMRAM is not affected directly by the lock, it is just notified.
>> However, either the code or the specification should be slightly updated to be in sync. A code update might require review of the caller assumptions, just to be sure.
>> 
>> I have a different concern though and hope I'm actually overlooking something.
>> If I understand the code correctly, it is the Platform BDS that exposes the (S)MmReadyToLock protocol. PiSmmIpl seems to consume that event and lock SMM resources based on the event.
>> Because of latter being an event however, I don't think it is, or can be, guaranteed to be the last event group member executing.
>> When it is not the last, the "about to be locked" part is not true for any subsequent callbacks, that could actually be a risky break of the specification - if it is.
>> If it is a break of the specification, I can only think of letting Platform BDS expose an "internal" event group, which is only caught by PiSmmIpl, which then drives the actual SmmReadyToLock flow.
>> This would require updates to all platform trees and hence I would propose a temporary backwards-compatibility.
>> 
>> Any comments? Did I overlook something (I hope)?
>> 
> 
> Mavvin,
> 
> You are correct there is no guarantee of order in events. Thanks for cc'ing the right folks, as I don't remember all the low level details...
> 
> In general the idea behind the MM code is it only comes from the platform, then by definition that code should be aware when the platform was going to lock MM. In a practical sense any MM module that had a depex evaluate to true would have dispatched in DXE prior to BDS being launched. In general BDS is the code that enumerates PCI and connects devices, thus there is no chance for 3rd party software to run before that point in the boot. So in an abstract sense that lock represents the end of DXE dispatch.
> 
> We probably need to reread the PI spec and make sure the spec is following the letter of the law, but I'd guess locking earlier is likely OK. 
> 

Sorry I meant edk2, not spec, following the letter of the law.

Thanks,

Andrew Fish

> Thanks,
> 
> Andrew Fish
> 
>> Thanks and regards,
>> Marvin
>> 
>>> -----Original Message-----
>>> From: edk2-devel <edk2-devel-bounces@lists.01.org> On Behalf Of
>>> Abhishek Singh
>>> Sent: Saturday, May 26, 2018 5:05 PM
>>> To: edk2-devel@lists.01.org
>>> Subject: [edk2] smm lock query
>>> 
>>> Hi,
>>> 
>>> This is the first time I am mailing to this list. If this is not the right place for the
>>> kind of questions I am asking please let me know where to direct my queries.
>>> 
>>> I have been looking at the SMM IPL code and a portion of the code is a little
>>> confusing to me. In the function SmmIplReadyToLockEventNotify, smram is
>>> locked (mSmmAccess->Lock) before the ready to lock notifications are sent
>>> through SmmIplGuidedEventNotify. Shouldn't the lock be placed after the
>>> ready to lock notifications?
>>> 
>>> Best regards,
>>> Abhishek
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>>> edk2-devel mailing list
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