Re: [PATCH][RFC] parisc: Use local tlb purges only on PA2.0 machines

[Helge Deller <deller@gmx.de>]

On 9/25/22 22:02, John David Anglin wrote:
> On 2022-09-25 2:57 p.m., Helge Deller wrote:
>> +#ifdef CONFIG_PA20
>> +#define ALT_COND_PACACHE    ALT_COND_ALWAYS
>> +#else
>> +#define ALT_COND_PACACHE    ALT_COND_NO_SMP
>> +#endif
>> +
>>   ENTRY_CFI(flush_tlb_all_local)
>>       /*
>>        * The pitlbe and pdtlbe instructions should only be used to
>> @@ -539,15 +545,10 @@ ENTRY_CFI(copy_user_page_asm)
>>
>>       /* Purge any old translations */
>>
>> -#ifdef CONFIG_PA20
>> -    pdtlb,l        %r0(%r28)
>> -    pdtlb,l        %r0(%r29)
>> -#else
>>   0:    pdtlb        %r0(%r28)
>>   1:    pdtlb        %r0(%r29)
>> -    ALTERNATIVE(0b, 0b+4, ALT_COND_NO_SMP, INSN_PxTLB)
>> -    ALTERNATIVE(1b, 1b+4, ALT_COND_NO_SMP, INSN_PxTLB)
>> -#endif
>> +    ALTERNATIVE(0b, 0b+4, ALT_COND_PACACHE, INSN_PxTLB)
>> +    ALTERNATIVE(1b, 1b+4, ALT_COND_PACACHE, INSN_PxTLB)
> This doesn't look correct.  If ALT_COND_PACACHE is defined as ALT_COND_NO_SMP, the pdtlb
> instructions will be converted to pdtlb,l instructions when running UP.  These are not supported
> on PA 1.1. 

Your concern is correct, but there is an additonal check in the alternative-coding,
which prevents enabling the local flag if we're not running on a PA2.0 CPU.
So, those ALTERNATIVE() macros will only apply on PA2.0 machines.

> When running SMP, we have pdtlb purges.  For these, we need bus serialization.
> 
> These also don't look correct:
> 
> #define pdtlb(sr, addr) asm volatile("pdtlb 0(%%sr%0,%1)" \
>                          ALTERNATIVE(ALT_COND_NO_SMP, INSN_PxTLB) \
>                          : : "i"(sr), "r" (addr) : "memory")
> #define pitlb(sr, addr) asm volatile("pitlb 0(%%sr%0,%1)" \
>                          ALTERNATIVE(ALT_COND_NO_SMP, INSN_PxTLB) \
>                          ALTERNATIVE(ALT_COND_NO_SPLIT_TLB, INSN_NOP) \
>                          : : "i"(sr), "r" (addr) : "memory")
> 
> We only have local purge on PA 2.0 machines.

Same as above.

Helge