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It's kind of interesting how many general Linux bugs and problems we're running into and fixing as Asahi. Nothing huge, but there's the whole >4K page support issue in random software (which we're pushing on purpose), BTI issues in mesa, lots of random kernel bugs...

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Hector Martin

@marcan42

Aug 1

A lot of this is really just "real people are now using Linux on a real, modern ARM64 platform". Up until now there just hasn't been anything *modern* running real distros and a near-upstream kernel. Apple machines are ARMv8.5-A, everything else desktop is stuck on <=ARMv8.2-A.

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Non-Apple mobile devices were only using ARMv8.2 until this year. Snapdragon is on ARMv9 now but most vendors aren't interested in MTE, PAC, BTI, etc. AOSP supports them but they'll end up launching with Pixels and Pixels launch in October so they haven't been moved to ARMv9 yet.

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Android works with upstream kernels including mainline but it can't be shipped in production because it's missing CTS mandated security features such as type-based CFI on x86_64 (not upstream) / arm64 (incomplete upstream) and also some minor things like perf_event_paranoid=3.

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The non-hardening stuff was either landed upstream or replaced with BPF such as uid (per-profile-per-app) based network statistics, gid-based socket restrictions for the INTERNET permission (no longer gid-based though) and a bunch of other stuff including most use of netfilter.

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Pixel 6 used 5.10 LTS since it was latest at the time but they've published experimental 5.15 LTS support. Kernel itself is a GKI (cross-device) and out-of-tree modules are built against the stable ABI. Latest Android 12 5.10 GKI is android.googlesource.com/kernel/common/ based on 5.10.117.

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Pixel 7 would launch with the Android 13 5.15 LTS. They might move to 5.15 LTS for Pixel 6 too. You can fairly easily boot the 5.19 mainline GKI on a Pixel 6 but for full functionality you'd need to fully update out-of-tree module source trees to the 5.19 GKI ABI from 5.15 one.

2:53 AM · Aug 2, 2022Twitter Web App

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The way it works is that the GKI ABI is guaranteed to be stable for the entire LTS branch lifetime so you can update the GKI separately from the modules. Can see the main difference from kernel.org LTS vs. GKI LTS is that GKI LTS adds the ABI padding and enforcement.

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Greg KH does most of the GKI branch maintenance alongside doing the upstream LTS releases. He releases both around the same time, but Android doesn't consider that to be a stable release. Goes through a few weeks of a stable branch and becomes monthly GKI branch with stable tags.

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