fix: classify KVM_RUN failures by whether the timer fired, not was armed - #92
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perbu wants to merge 1 commit into
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fix: classify KVM_RUN failures by whether the timer fired, not was armed#92perbu wants to merge 1 commit into
perbu wants to merge 1 commit into
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run_once() tested timer_ticks, which holds the *configured* timeout in ms, so every KVM_RUN failure inside a timed run was thrown as "Timeout Exception" and its errno discarded - an EFAULT from a guest touch of protected or unbacked host memory in particular became indistinguishable from a slow request. Now a timeout requires the timer to have actually fired (the SIGUSR2 handler's thread_local, or EINTR with a timer armed); everything else keeps its errno and routes to the existing EFAULT / generic branches. errno is captured inside the ioctl scope before the profiler's destructor can overwrite it. Genuine timeouts still throw MachineTimeoutException with unchanged message and data. arm64 mirror transcribed from the amd64 shape; not build-verified here (no aarch64 toolchain on this box). Found while testing VmGroup PerGroup guard bands, where the band fault surfaces as -EFAULT from KVM_RUN and the relabel would have been a diagnosability regression. Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
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Step 1 of the ladder in #91. Standalone.
run_once() tested timer_ticks, which holds the configured timeout, so every KVM_RUN failure inside a timed run threw Timeout Exception and discarded errno — a guest EFAULT was indistinguishable from a slow request. A timeout now requires the timer to have actually fired (the SIGUSR2 handler's thread_local, or EINTR with a timer armed); everything else keeps its errno and routes to the existing EFAULT/generic branches. errno is captured inside the ioctl scope, before the profiler destructor can overwrite it.
Same treatment on arm64. Unit suite on x86-64 matches the master baseline; the arm64 side was validated on an Asahi host on the original branch.
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