fix: init v8 platform once on main thread #20495
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bartlomieju
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bartlomieju
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Sep 14, 2023
mmastrac
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Jan 24, 2024
Due to V8's PKU feature, only the thread that initialized the V8 platform or those spawned from it can access the isolates; other threads will get a segmentation fault. Since each test runs in its thread, they crash on newer CPUs that support PKU. This issue has two possible solutions: 1. Initialize the platform once in the main thread. 2. Turn off the PKU feature during testing. This issue was already encountered for the `deno test` command, which was resolved by initializing the platform in the main thread (denoland/deno#20495). In the case of rust tests, the same solution cannot be used, as the default test runner does not allow running code on the main thread before any test runs. My proposed solution is to add a feature flag to deno_core, which, when enabled, uses the unprotected platform. An alternative solution could be to call `deno_core::JsRuntime::init_platform` at the beginning of each test. This PR will also be a step towards fixing denoland/deno#21439
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This is a mitigation for segfaults happening in V8 on CPU with MPK (memory protected keys).
After much trail and error we found that unless V8 platform is initialized on main thread the
segfaults start appears once JIT kicks in. "deno test" and "deno bench" were impacted by
this problem.
Fixes #19926
Fixes #20243
Fixes #20450