[PATCH v2] arm64: treat PF_IO_WORKER like PF_KTHREAD for mitigations

[Jens Axboe]

Like PF_KTHREAD, PF_IO_WORKER never exit to userspace. They exist
entirely within the kernel, and hence don't need any task mitigations
applied.

Signed-off-by: Jens Axboe <axboe at kernel.dk>

---

v2: include ssbs_thread_switch() too

diff --git a/arch/arm64/kernel/process.c b/arch/arm64/kernel/process.c
index 71d59b5abede..9ce614b2177e 100644
--- a/arch/arm64/kernel/process.c
+++ b/arch/arm64/kernel/process.c
@@ -445,9 +445,11 @@ static void ssbs_thread_switch(struct task_struct *next)
 {
 	/*
 	 * Nothing to do for kernel threads, but 'regs' may be junk
-	 * (e.g. idle task) so check the flags and bail early.
+	 * (e.g. idle task) so check the flags and bail early. Nothing to do
+	 * for IO worker threads either, as they never transition between
+	 * kernel and userspace.
 	 */
-	if (unlikely(next->flags & PF_KTHREAD))
+	if (unlikely(next->flags & (PF_KTHREAD | PF_IO_WORKER)))
 		return;
 
 	/*
diff --git a/arch/arm64/kernel/proton-pack.c b/arch/arm64/kernel/proton-pack.c
index fca9cc6f5581..25a21c3d446c 100644
--- a/arch/arm64/kernel/proton-pack.c
+++ b/arch/arm64/kernel/proton-pack.c
@@ -654,7 +654,7 @@ static void __update_pstate_ssbs(struct pt_regs *regs, bool state)
 void spectre_v4_enable_task_mitigation(struct task_struct *tsk)
 {
 	struct pt_regs *regs = task_pt_regs(tsk);
-	bool ssbs = false, kthread = tsk->flags & PF_KTHREAD;
+	bool ssbs = false, kthread = tsk->flags & (PF_KTHREAD | PF_IO_WORKER);
 
 	if (spectre_v4_mitigations_off())
 		ssbs = true;

-- 
Jens Axboe