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

[Nicholas Piggin]

Excerpts from Aneesh Kumar K.V's message of May 4, 2020 5:27 pm:
> Nicholas Piggin <npiggin at gmail.com> writes:
> 
>> 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 at gmail.com>
> 
> ....
> 
>> +{
>> +	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.

>> +{
>> +	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