Re: [PATCH v2 5/6] mm: tlb: Provide flush_*_tlb_range wrappers

[Zhenyu Ye]

Hi Catalin,

Sorry for taking so long to reply to you.

On 2020/5/26 22:52, Catalin Marinas wrote:
> On Mon, May 25, 2020 at 03:19:42PM +0800, Zhenyu Ye wrote:
>>
>> tlb_flush_##_pxx##_range() is used to set tlb->cleared_*,
>> flush_##_pxx##_tlb_range() will actually flush the TLB entry.
>>
>> In arch64, tlb_flush_p?d_range() is defined as:
>>
>> 	#define flush_pmd_tlb_range(vma, addr, end)	flush_tlb_range(vma, addr, end)
>> 	#define flush_pud_tlb_range(vma, addr, end)	flush_tlb_range(vma, addr, end)
> 
> Currently, flush_p??_tlb_range() are generic and defined as above. I
> think in the generic code they can remain an alias for
> flush_tlb_range().
> 
> On arm64, we can redefine them as:
> 
> #define flush_pte_tlb_range(vma, addr, end)	__flush_tlb_range(vma, addr, end, 3)
> #define flush_pmd_tlb_range(vma, addr, end)	__flush_tlb_range(vma, addr, end, 2)
> #define flush_pud_tlb_range(vma, addr, end)	__flush_tlb_range(vma, addr, end, 1)
> #define flush_p4d_tlb_range(vma, addr, end)	__flush_tlb_range(vma, addr, end, 0)
> 
> (unless the compiler optimises away all the mmu_gather stuff in your
> macro above but they don't look trivial to me)
> 

I changed generic code before considering that other structures may also
use this feature, such as Power9. And Peter may want to replace all
flush_tlb_range() by tlb_flush() in the future, see [1] for details.

If only enable this feature on aarch64, your codes are better.

[1] https://lore.kernel.org/linux-arm-kernel/20200402163849.GM20713@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx/

> Also, I don't see the new flush_pte_* and flush_p4d_* macros used
> anywhere and I don't think they are needed. The pte equivalent is
> flush_tlb_page() (we need to make sure it's not used on a pmd in the
> hugetlb context).
> 

flush_tlb_page() is used to flush only one page.  If we add the flush_pte_tlb_range(),
then we can use it to flush a range of pages in the future.

But flush_pte_* and flush_p4d_* macros are really not used anywhere.
I will remove them in next version of series, and add them if someone needs.

>> So even if we know the level here, we can not pass the value to tlbi
>> instructions (flush_tlb_range() is a common kernel interface and retro-fit it
>> needs lots of changes), according to Peter's suggestion, I finally decide to
>> pass the value of TTL by the tlb_gather_* frame.[1]
> 
> My comment was about the generic implementation using mmu_gather as you
> are proposing. We don't need to change the flush_tlb_range() interface,
> nor do we need to rewrite flush_p??_tlb_range().
> 

Thanks,
Zhenyu