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SubjectRe: [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@codeaurora.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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