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Bae wrote: >Sean reported [1] the following splat when running KVM tests: > > WARNING: CPU: 232 PID: 15391 at xfd_validate_state+0x65/0x70 > Call Trace: > > fpu__clear_user_states+0x9c/0x100 > arch_do_signal_or_restart+0x142/0x210 > exit_to_user_mode_loop+0x55/0x100 > do_syscall_64+0x205/0x2c0 > entry_SYSCALL_64_after_hwframe+0x4b/0x53 > >Chao further identified [2] a reproducible scenarios involving signal >delivery: a non-AMX task is preempted by an AMX-enabled task which >modifies the XFD MSR. > >When the non-AMX task resumes and reloads XSTATE with init values, >a warning is triggered due to a mismatch between fpstate::xfd and the >CPU's current XFD state. fpu__clear_user_states() does not currently >re-synchronize the XFD state after such preemption. > >Invoke xfd_update_state() which detects and corrects the mismatch if the >dynamic feature is enabled. > >This also benefits the sigreturn path, as fpu__restore_sig() may call >fpu__clear_user_states() when the sigframe is inaccessible. > >Fixes: 672365477ae8a ("x86/fpu: Update XFD state where required") >Reported-by: Sean Christopherson >Closes: https://lore.kernel.org/lkml/aDCo_SczQOUaB2rS@google.com [1] >Tested-by: Chao Gao >Signed-off-by: Chang S. Bae >Cc: stable@vger.kernel.org >Link: https://lore.kernel.org/all/aDWbctO%2FRfTGiCg3@intel.com [2] Reviewed-by: Chao Gao Thanks for looking into this issue.