Re: [PATCH 2/6] perf/x86/intel/pt: Stop tracing if VMXON has not yet happened

[sashiko-bot@kernel.org]

> On Broadwell, which does not support Intel PT in VMX operation
> (IA32_VMX_MISC[14] = 0), VMXON clears IA32_RTIT_CTL.TraceEn and any
> subsequent write to IA32_RTIT_CTL causes #GP.
> 
> To avoid that, intel_pt_handle_vmx() sets pt->vmx_on so that
> pt_config_start() and pt_config_stop() skip writes to
> IA32_RTIT_CTL while VMX is active.
> 
> However, pt->vmx_on is set before VMXON executes. An NMI in the window
> between setting pt->vmx_on and executing VMXON can then observe
> vmx_on == true while tracing is still enabled.
> 
> In that case pt_config_stop() skips the write that would clear TraceEn,
> leaving tracing active. This can subsequently cause:
> 
> [ ... ]
> 	 kthread+0x2cb/0x3a0
> 	 ret_from_fork+0x5ff/0x7f0
> 
> Fixes: 1c5ac21a0e9b ("perf/x86/intel/pt: Don't die on VMXON")
> Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>

Sashiko has reviewed this patch and found no issues.

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Sashiko AI review · https://sashiko.dev/#/patchset/20261102074039.26983-1-adrian.hunter@intel.com?part=2