On Tue, Nov 14, 2017 at 07:17:11AM -0800, James Bottomley wrote: > On Tue, 2017-11-14 at 16:59 +0200, Jarkko Sakkinen wrote: > > On Sat, Nov 11, 2017 at 01:31:32PM -0700, Jerry Snitselaar wrote: > > > > > > On Sat Nov 11 17, Jason Gunthorpe wrote: > > > > > > > > On Sat, Nov 11, 2017 at 12:12:57PM -0700, Jerry Snitselaar wrote: > > > > > > > > > > > > > > Before the release_locality code would only actually release > > > > > the locality if the request use bit was set. So after it > > > > > grabbed the locality during probe it probably never released > > > > > it. The idea with the new code was to release it when it was no > > > > > longer needed so another requester would be able to take the > > > > > tpm without having to wait for it to be released. > > > > > > > > If I recall, this was so that system level things outside linux > > > > could access the TPM properly?? > > > > > > > > > > Yes, that is what drove this initially. I believe Jarkko was also > > > thinking of the possibility in the future where something like a vm > > > could request a locality as well, but that is just a hazy > > > recollection of emails from back then. > > > > This was something I recall discussing in LPC 2016 in the hallway at > > least :-) A tidbit but it could make sense to tie it to VMM, not VM. > > I think we should be extremely wary of different localities before we > have a cast iron definition of what they mean. All the TPM PC spec > says is that locality 4 is reserved for firmware (meaning the kernel > should have no access) and it implies there's a privilege hierarchy, > making 4 the most privileged and 0 the least but leaves all the > definition to the OS. Since we only have four other localities to play > with, we need a global definition of what they mean in Linux (and who > protects them) otherwise we'll get conflicting uses. What does Windows > use them for? > > James No idea. If I had to guess, they use only one locality for OS as this what PTT/fTPM had when it didn't have localities. At least their implementation works with only one locality. /Jarkko
