Messages in this thread | | | Date | Wed, 31 Jan 2024 11:17:27 -0500 | From | Paul Gortmaker <> | Subject | Re: [PATCH 0/4] x86/alternatives: Do NOPs optimization on a temporary buffer |
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[[PATCH 0/4] x86/alternatives: Do NOPs optimization on a temporary buffer] On 30/01/2024 (Tue 11:59) Borislav Petkov wrote:
> From: "Borislav Petkov (AMD)" <bp@alien8.de> > > Hi, > > here's a small set which sprang out from my reacting to the fact that > NOPs optimization in the alternatives code needs to happen on > a temporary buffer like the other alternative operations - not in-place > and cause all kinds of fun. > > The result is this, which makes the alternatives code simpler and it is > a net win, size-wise: > > 1 file changed, 50 insertions(+), 72 deletions(-) > > > Constructive feedback is always welcome!
So, I figured I would set up the same reproducer, on the same machine; build and test a known broken NOP rewrite kernel like v6.5.0 to confirm I could still reproduce the boot fail in approximately 2% of runs. And then move to testing this series.
Well, much to my annoyance my plan broke down at step one. After about three hours and over 400 runs, I didn't get a single fail. I still had a known broken build from the original reporting in October of v6.5.7, so I let that run for over 300 iterations, and also didn't get any failures.
I have to assume that even though I'm using the same host, same scripts, that because I was testing on Yocto master, other things have changed since October - maybe binutils, qemu, the runqemu script, ... In theory, I could try and reset Yocto back to October-ish but that is probably of diminishing returns. And I can't unwind the host machine distro updates that have happened since October.
With hindsight and knowledge of what the issue was and how narrow the window was to trigger it, I guess this shouldn't be a surprise.
So as a "next best" effort, I let this rc1-alt-v2 branch run overnight, and after over 2200 iterations, I didn't get any boot fails.
Paul. --
> > Thx. > > Borislav Petkov (AMD) (4): > x86/alternatives: Use a temporary buffer when optimizing NOPs > x86/alternatives: Get rid of __optimize_nops() > x86/alternatives: Optimize optimize_nops() > x86/alternatives: Sort local vars in apply_alternatives() > > arch/x86/kernel/alternative.c | 122 ++++++++++++++-------------------- > 1 file changed, 50 insertions(+), 72 deletions(-) > > -- > 2.43.0 >
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