linux-kernel - Re: [PATCHv2 1/3] iommu/io-pgtable: Add a quirk to use tlb_flush

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Date:   Tue, 22 Jun 2021 12:41:22 +0530
From:   Sai Prakash Ranjan <saiprakash.ranjan@...eaurora.org>
To:     Robin Murphy <robin.murphy@....com>
Cc:     Will Deacon <will@...nel.org>, Joerg Roedel <joro@...tes.org>,
        Thierry Reding <treding@...dia.com>,
        linux-arm-msm@...r.kernel.org,
        Douglas Anderson <dianders@...omium.org>,
        linux-kernel@...r.kernel.org, iommu@...ts.linux-foundation.org,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCHv2 1/3] iommu/io-pgtable: Add a quirk to use
 tlb_flush_all() for partial walk flush

Hi Robin,

On 2021-06-21 21:15, Robin Murphy wrote:
> On 2021-06-18 03:51, Sai Prakash Ranjan wrote:
>> Add a quirk IO_PGTABLE_QUIRK_TLB_INV_ALL to invalidate entire context
>> with tlb_flush_all() callback in partial walk flush to improve unmap
>> performance on select few platforms where the cost of 
>> over-invalidation
>> is less than the unmap latency.
> 
> I still think this doesn't belong anywhere near io-pgtable at all.
> It's a driver-internal decision how exactly it implements a non-leaf
> invalidation, and that may be more complex than a predetermined
> boolean decision. For example, I've just realised for SMMUv3 we can't
> invalidate multiple levels of table at once with a range command,
> since if we assume the whole thing is mapped at worst-case page
> granularity we may fail to invalidate any parts which are mapped as
> intermediate-level blocks. If invalidating a 1GB region (with 4KB
> granule) means having to fall back to 256K non-range commands, we may
> not want to invalidate by VA then, even though doing so for a 2MB
> region is still optimal.
> 
> It's also quite feasible that drivers might want to do this for leaf
> invalidations too - if you don't like issuing 512 commands to
> invalidate 2MB, do you like issuing 511 commands to invalidate 2044KB?
> - and at that point the logic really has to be in the driver anyway.
> 

Ok I will move this to tlb_flush_walk() functions in the drivers. In the 
previous
v1 thread, you suggested to make the choice in iommu_get_dma_strict() 
test,
I assume you meant the test in iommu_dma_init_domain() with a flag or 
was it
the leaf driver(ex:arm-smmu.c) test of iommu_get_dma_strict() in 
init_domain?

I am still a bit confused on where this flag would be? Should this be a 
part
of struct iommu_domain?

Thanks,
Sai

> 
>> Signed-off-by: Sai Prakash Ranjan <saiprakash.ranjan@...eaurora.org>
>> ---
>>   drivers/iommu/io-pgtable-arm.c | 3 ++-
>>   include/linux/io-pgtable.h     | 5 +++++
>>   2 files changed, 7 insertions(+), 1 deletion(-)
>> 
>> diff --git a/drivers/iommu/io-pgtable-arm.c 
>> b/drivers/iommu/io-pgtable-arm.c
>> index 87def58e79b5..5d362f2214bd 100644
>> --- a/drivers/iommu/io-pgtable-arm.c
>> +++ b/drivers/iommu/io-pgtable-arm.c
>> @@ -768,7 +768,8 @@ arm_64_lpae_alloc_pgtable_s1(struct io_pgtable_cfg 
>> *cfg, void *cookie)
>>   	if (cfg->quirks & ~(IO_PGTABLE_QUIRK_ARM_NS |
>>   			    IO_PGTABLE_QUIRK_NON_STRICT |
>>   			    IO_PGTABLE_QUIRK_ARM_TTBR1 |
>> -			    IO_PGTABLE_QUIRK_ARM_OUTER_WBWA))
>> +			    IO_PGTABLE_QUIRK_ARM_OUTER_WBWA |
>> +			    IO_PGTABLE_QUIRK_TLB_INV_ALL))
>>   		return NULL;
>>     	data = arm_lpae_alloc_pgtable(cfg);
>> diff --git a/include/linux/io-pgtable.h b/include/linux/io-pgtable.h
>> index 4d40dfa75b55..45441592a0e6 100644
>> --- a/include/linux/io-pgtable.h
>> +++ b/include/linux/io-pgtable.h
>> @@ -82,6 +82,10 @@ struct io_pgtable_cfg {
>>   	 *
>>   	 * IO_PGTABLE_QUIRK_ARM_OUTER_WBWA: Override the outer-cacheability
>>   	 *	attributes set in the TCR for a non-coherent page-table walker.
>> +	 *
>> +	 * IO_PGTABLE_QUIRK_TLB_INV_ALL: Use TLBIALL/TLBIASID to invalidate
>> +	 *	entire context for partial walk flush to increase unmap
>> +	 *	performance on select few platforms.
>>   	 */
>>   	#define IO_PGTABLE_QUIRK_ARM_NS		BIT(0)
>>   	#define IO_PGTABLE_QUIRK_NO_PERMS	BIT(1)
>> @@ -89,6 +93,7 @@ struct io_pgtable_cfg {
>>   	#define IO_PGTABLE_QUIRK_NON_STRICT	BIT(4)
>>   	#define IO_PGTABLE_QUIRK_ARM_TTBR1	BIT(5)
>>   	#define IO_PGTABLE_QUIRK_ARM_OUTER_WBWA	BIT(6)
>> +	#define IO_PGTABLE_QUIRK_TLB_INV_ALL	BIT(7)
>>   	unsigned long			quirks;
>>   	unsigned long			pgsize_bitmap;
>>   	unsigned int			ias;
>> 

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