Re: [PATCH v6] arm64: Add support for new control bits CTR_EL0.DIC and CTR_EL0.IDC

[Shanker Donthineni]

Hi Will,

On 03/06/2018 09:23 AM, Will Deacon wrote:
> Hi Shanker,
> 
> On Tue, Mar 06, 2018 at 08:47:27AM -0600, Shanker Donthineni wrote:
>> On 03/06/2018 07:44 AM, Will Deacon wrote:
>>> I think this is a slight asymmetry with the code for the I-side. On the
>>> I-side, you hook into invalidate_icache_by_line, whereas on the D-side you
>>> hook into the callers of dcache_by_line_op. Why is that?
>>>
>>
>> There is no particular reason other than complexity of the macro with another 
>> alternative. I tried to avoid this change by updating __clean_dcache_area_pou().
>> I can change if you're interested to see both I-Side and D-Side changes are
>> symmetric some thing like this...
>>
>>  .macro dcache_by_line_op op, domain, kaddr, size, tmp1, tmp2
>>   
>>   .if	(\op == cvau)
>>   alternative_if ARM64_HAS_CACHE_IDC
>>         dsb	ishst
>>         b       9997f
>>   alternative_else_nop_endif
>>   .endif
>>
>> 	dcache_line_size \tmp1, \tmp2
>> 	add	\size, \kaddr, \size
>> 	sub	\tmp2, \tmp1, #1
>> 	bic	\kaddr, \kaddr, \tmp2
>>  9998:
>> 	.if	(\op == cvau || \op == cvac)
>>  alternative_if_not ARM64_WORKAROUND_CLEAN_CACHE
>> 	dc	\op, \kaddr
>>  alternative_else
>> 	dc	civac, \kaddr
>>  alternative_endif
>> 	.elseif	(\op == cvap)
>>  alternative_if ARM64_HAS_DCPOP
>> 	sys 3, c7, c12, 1, \kaddr	// dc cvap
>>  alternative_else
>> 	dc	cvac, \kaddr
>>  alternative_endif
>> 	.else
>> 	dc	\op, \kaddr
>> 	.endif
>> 	add	\kaddr, \kaddr, \tmp1
>> 	cmp	\kaddr, \size
>> 	b.lo	9998b
>> 	dsb	\domain
>> 9997:
>> 	.endm
> 
> I think it would be cleaner the other way round, actually -- move the check
> out of invalidate_icache_by_line and into its two callers.
> 

Sure, I'll send out the next patch with your suggestions.

>>> I notice that the only user other than
>>> flush_icache_range/__flush_cache_user_range or invalidate_icache_by_line
>>> is in KVM, via invalidate_icache_range. If you want to hook in there, why
>>> aren't you also patching __flush_icache_all? If so, I'd rather have the
>>> I-side code consistent with the D-side code and do this in the handful of
>>> callers. We might even be able to elide a branch or two that way.
>>>
>>
>> Agree with you, it saves function calls overhead. I'll do this change...
>>
>> static void invalidate_icache_guest_page(kvm_pfn_t pfn, unsigned long size)
>> {
>> 	if (cpus_have_const_cap(ARM64_HAS_CACHE_DIC)
>> 	    __invalidate_icache_guest_page(pfn, size);
>> }
>>
>>
>>> I'm going to assume that I-cache aliases are all coherent if DIC=1, so it's
>>> safe to elide our alias sync code.
>>>
>>
>> I'm not sure about I-cache whether aliases are all coherent if DIC=1 ot not.
>> Unfortunately I don't have any hardware to test DIC=1. I've verified IDC=1.
> 
> I checked with our architects and aliases don't pose a problem here, so you
> can ignore me :)
> 

I also confirmed with Thomas Speier, we can skip __flush_icache_all() if DIC=1.

 
> Will
> 
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> 

-- 
Shanker Donthineni
Qualcomm Datacenter Technologies, Inc. as an affiliate of Qualcomm Technologies, Inc.
Qualcomm Technologies, Inc. is a member of the Code Aurora Forum, a Linux Foundation Collaborative Project.