linux-kernel - Re: [PATCH v2 5/6] mm: tlb: Provide flush_*_tlb

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Date:   Mon, 25 May 2020 15:19:42 +0800
From:   Zhenyu Ye <yezhenyu2@...wei.com>
To:     Catalin Marinas <catalin.marinas@....com>
CC:     <peterz@...radead.org>, <mark.rutland@....com>, <will@...nel.org>,
        <aneesh.kumar@...ux.ibm.com>, <akpm@...ux-foundation.org>,
        <npiggin@...il.com>, <arnd@...db.de>, <rostedt@...dmis.org>,
        <maz@...nel.org>, <suzuki.poulose@....com>, <tglx@...utronix.de>,
        <yuzhao@...gle.com>, <Dave.Martin@....com>, <steven.price@....com>,
        <broonie@...nel.org>, <guohanjun@...wei.com>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>, <linux-arch@...r.kernel.org>,
        <linux-mm@...ck.org>, <arm@...nel.org>, <xiexiangyou@...wei.com>,
        <prime.zeng@...ilicon.com>, <zhangshaokun@...ilicon.com>,
        <kuhn.chenqun@...wei.com>
Subject: Re: [PATCH v2 5/6] mm: tlb: Provide flush_*_tlb_range wrappers

On 2020/5/22 23:42, Catalin Marinas wrote:
> On Thu, Apr 23, 2020 at 09:56:55PM +0800, Zhenyu Ye wrote:
>> diff --git a/mm/pgtable-generic.c b/mm/pgtable-generic.c
>> index 3d7c01e76efc..3eff199d3507 100644
>> --- a/mm/pgtable-generic.c
>> +++ b/mm/pgtable-generic.c
>> @@ -101,6 +101,28 @@ pte_t ptep_clear_flush(struct vm_area_struct *vma, unsigned long address,
>>  
>>  #ifdef CONFIG_TRANSPARENT_HUGEPAGE
>>  
>> +#ifndef __HAVE_ARCH_FLUSH_PMD_TLB_RANGE
>> +
>> +#define FLUSH_Pxx_TLB_RANGE(_pxx)					\
>> +void flush_##_pxx##_tlb_range(struct vm_area_struct *vma,		\
>> +			      unsigned long addr, unsigned long end)	\
>> +{									\
>> +		struct mmu_gather tlb;					\
>> +									\
>> +		tlb_gather_mmu(&tlb, vma->vm_mm, addr, end);		\
>> +		tlb_start_vma(&tlb, vma);				\
>> +		tlb_flush_##_pxx##_range(&tlb, addr, end - addr);	\
>> +		tlb_end_vma(&tlb, vma);					\
>> +		tlb_finish_mmu(&tlb, addr, end);			\
>> +}
> 
> I may have confused myself (flush_p??_tlb_* vs. tlb_flush_p??_*) but do
> actually need this whole tlb_gather thing here? IIUC (by grep'ing),
> flush_p?d_tlb_range() is only called on huge pages, so we should know
> the level already.
> 

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)

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]

[1] https://lore.kernel.org/linux-arm-kernel/20200331142927.1237-1-yezhenyu2@huawei.com/

Thanks,
Zhenyu