Re: [PATCH 1/2] powerpc/64s/hash: add torture_slb kernel boot option to increase SLB faults

Excerpts from Aneesh Kumar K.V's message of May 4, 2020 5:27 pm:

Nicholas Piggin [off-list ref] writes:

quoted

This option increases the number of SLB misses by limiting the number of
kernel SLB entries, and increased flushing of cached lookaside information.
This helps stress test difficult to hit paths in the kernel.

Signed-off-by: Nicholas Piggin <npiggin@gmail.com>

....

quoted

+{
+	unsigned long slbie_data = get_paca()->slb_cache[index];
+	unsigned long ksp = get_paca()->kstack;
+
+	slbie_data <<= SID_SHIFT;
+	slbie_data |= 0xc000000000000000ULL;
+	if ((ksp & slb_esid_mask(mmu_kernel_ssize)) == slbie_data)
+		return;
+	slbie_data |= mmu_kernel_ssize << SLBIE_SSIZE_SHIFT;
+
+	asm volatile("slbie %0" : : "r" (slbie_data));
+}
+
+static void slb_cache_slbie(unsigned int index)

May be slb_cache_slbie_user()? Similar to _kernel above?

Yeah that'd help.

quoted

+{
+	unsigned long slbie_data = get_paca()->slb_cache[index];
+
+	slbie_data <<= SID_SHIFT;
+	slbie_data |= user_segment_size(slbie_data) << SLBIE_SSIZE_SHIFT;
+	slbie_data |= SLBIE_C; /* user slbs have C=1 */
+
+	asm volatile("slbie %0" : : "r" (slbie_data));
+}
 
 /* Flush all user entries from the segment table of the current processor. */
 void switch_slb(struct task_struct *tsk, struct mm_struct *mm)

@@ -414,8 +449,14 @@ void switch_slb(struct task_struct *tsk, struct mm_struct *mm)
 	 * which would update the slb_cache/slb_cache_ptr fields in the PACA.
 	 */
 	hard_irq_disable();
-	asm volatile("isync" : : : "memory");
-	if (cpu_has_feature(CPU_FTR_ARCH_300)) {
+	isync();
+	if (torture_slb()) {
+		__slb_flush_and_restore_bolted(0);

s/0/SLIBA_IH_ALL or something like that? 

IH isn't so simple. 0 isn't all, it's clear all SLBE except index zero, 
and flush all EA lookaside data.

Maybe callers should use a bool parameter though to flush kernel 
lookaside data.

Thanks,
Nick