Re: [PATCH 5.10 096/126] KVM: x86/mmu: Use atomic ops to set SPTEs in TDP MMU map

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On Tue, Apr 06, 2021 at 05:48:50PM +0200, Paolo Bonzini wrote:
On 06/04/21 15:49, Sasha Levin wrote:
Yup. Is there anything wrong with those patches?

The big issue, and the one that you ignoredz every time we discuss this topic, is that this particular subset of 17 has AFAIK never been tested by anyone.

Few of the CI systems that run on stable(-rc) releases run
kvm-unit-tests, which passed. So yes, this was tested.

There's plenty of locking changes in here, one patch that you didn't backport has this in its commit message:

  This isn't technically a bug fix in the current code [...] but that
  is all very, very subtle, and will break at the slightest sneeze,

meaning that the locking in 5.10 and 5.11 was also less robust to changes elsewhere in the code.

Let's also talk about the process and the timing. I got the "failed to apply" automated message last Friday and I was going to work on the backport today since yesterday was a holiday here. I was *never* CCed

There are a few more "FAILED:" mails that need attention that are older
than this one, I hope they're also in the queue.

on a post of this backport for maintainers to review; you guys

You're looking at it, this is the -rc cycle for stable kernels.

*literally* took random subsets of patches from a feature that is new and in active development, and hoped that they worked on a past release.

Right, I looked at what needed to be backported, took it back to 5.4,
and ran kvm-unit-tests on it.

What other hoops should we jump through so we won't need to "hope"
anymore?

I could be happy because you just provided me with a perfect example of why to use my employer's franken-kernel instead of upstream stable kernels... ;) but this is not how a world-class operating system is developed. Who cares if a VM breaks or even if my laptop panics; but I'd seriously fear for my data if you applied the same attitude to XFS or ext4fs.

For now, please drop all 17 patches from 5.10 and 5.11. I'll send a tested backport as soon as possible.

Sure, I'll drop them. Please let us know when a backport is available.

--
Thanks,
Sasha



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