ARM: 7306/1: vfp: flush thread hwstate before restoring context from sigframe
Following execution of a signal handler, we currently restore the VFP context from the ucontext in the signal frame. This involves copying from the user stack into the current thread's vfp_hard_struct and then flushing the new data out to the hardware registers. This is problematic when using a preemptible kernel because we could be context switched whilst updating the vfp_hard_struct. If the current thread has made use of VFP since the last context switch, the VFP notifier will copy from the hardware registers into the vfp_hard_struct, overwriting any data that had been partially copied by the signal code. Disabling preemption across copy_from_user calls is a terrible idea, so instead we move the VFP thread flush *before* we update the vfp_hard_struct. Since the flushing is performed lazily, this has the effect of disabling VFP and clearing the CPU's VFP state pointer, therefore preventing the thread from being updated with stale data on the next context switch. Cc: stable <stable@vger.kernel.org> Tested-by:Peter Maydell <peter.maydell@linaro.org> Signed-off-by:
Will Deacon <will.deacon@arm.com> Signed-off-by:
Russell King <rmk+kernel@arm.linux.org.uk>
parent
97f10409
Please register or sign in to comment