Re: [regression] significant delays when secureboot is enabled since 6.10

Jarkko Sakkinen
2024-09-22T14:11:51Z

On Sat Sep 21, 2024 at 6:40 PM EEST, Jarkko Sakkinen wrote:
> On Sun Sep 15, 2024 at 7:22 PM EEST, Jarkko Sakkinen wrote:
> > On Sun Sep 15, 2024 at 6:00 PM EEST, James Bottomley wrote:
> > > On Sun, 2024-09-15 at 17:50 +0300, Jarkko Sakkinen wrote:
> > > > On Sun Sep 15, 2024 at 4:59 PM EEST, James Bottomley wrote:
> > > > > On Sun, 2024-09-15 at 13:07 +0300, Jarkko Sakkinen wrote:
> > > > > > On Sun Sep 15, 2024 at 12:43 PM EEST, Jarkko Sakkinen wrote:
> > > > > > > When it comes to boot we should aim for one single
> > > > > > > start_auth_session during boot, i.e. different phases would
> > > > > > > leave that session open so that we don't have to load the
> > > > > > > context every single time.  I think it should be doable.
> > > > > >
> > > > > > The best possible idea how to improve performance here would be
> > > > > > to transfer the cost from time to space. This can be achieved by
> > > > > > keeping null key permanently in the TPM memory during power
> > > > > > cycle.
> > > > >
> > > > > No it's not at all.  If you look at it, the NULL key is only used
> > > > > to encrypt the salt for the start session and that's the operating
> > > > > taking a lot of time.  That's why the cleanest mitigation would be
> > > > > to save and restore the session.  Unfortunately the timings you
> > > > > already complain about still show this would be about 10x longer
> > > > > than a no-hmac extend so I'm still waiting to see if IMA people
> > > > > consider that an acceptable tradeoff.
> > > >
> > > > The bug report does not say anything about IMA issues. Please read
> > > > the bug reports before commenting ;-) I will ignore your comment
> > > > because it is plain misleading information.
> > > >
> > > > https://bugzilla.kernel.org/show_bug.cgi?id=219229
> > >
> > > Well, given that the kernel does no measured boot extends after the EFI
> > > boot stub (which isn't session protected) finishes, what's your theory
> > > for the root cause?
> >
> > I don't think there is a silver bullet. Based on benchmark which showed
> > 80% overhead from throttling the context reducing number of loads and
> > saves will cut a slice of the fat.
> >
> > Since it is the low-hanging fruit I'll start with that. In other words,
> > I'm not going touch session loading and saving. I'll start with null
> > key loading and saving.
>
> "my theory" worked pretty well. It brought the boot time back to 8.7s,
> which can be explained with encryption overhead pretty well.
>
> I'd suggest reading the bug report next time before solving a problem
> that did not exist. We care about users, not unfinished patch sets.

I'd also expect to review a patch set that fixes a performance issue
caused by a feature that you implemented less than a one week. One that
doubles the boot time on AMD CPU's.

This is ridiculous tbh.

BR, Jarkko