Commit e4787e71 authored by Rashmica Gupta's avatar Rashmica Gupta Committed by Michael Ellerman
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powerpc/signal: Update comment for clarity 



The comment being referred to was deleted in commit af1bbc3d ("powerpc:
Remove UP only lazy floating point and vector optimisations").

Add a bit more detail so it's clear why we need to clear the FP/VEC/VSX
bits here.

Signed-off-by: default avatarRashmica Gupta <rashmica@linux.ibm.com>
Signed-off-by: default avatarMichael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20220617043135.426897-1-rashmica@linux.ibm.com
parent fcdb758c

arch/powerpc/kernel/signal_64.c

+6 −3
Original line number Diff line number Diff line
@@ -377,9 +377,12 @@ static long notrace __unsafe_restore_sigcontext(struct task_struct *tsk, sigset_ 
		unsafe_get_user(set->sig[0], &sc->oldmask, efault_out);



	/*

	 * Force reload of FP/VEC.

	 * This has to be done before copying stuff into tsk->thread.fpr/vr

	 * for the reasons explained in the previous comment.

	 * Force reload of FP/VEC/VSX so userspace sees any changes.

	 * Clear these bits from the user process' MSR before copying into the

	 * thread struct. If we are rescheduled or preempted and another task

	 * uses FP/VEC/VSX, and this process has the MSR bits set, then the

	 * context switch code will save the current CPU state into the

	 * thread_struct - possibly overwriting the data we are updating here.

	 */

	regs_set_return_msr(regs, regs->msr & ~(MSR_FP | MSR_FE0 | MSR_FE1 | MSR_VEC | MSR_VSX));