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Message-ID: <9c75a85e-5d80-0286-1ce5-89479d49170e@huawei.com>
Date: Tue, 31 Mar 2020 16:15:49 +0800
From: Zhenyu Ye <yezhenyu2@...wei.com>
To: Peter Zijlstra <peterz@...radead.org>, <schwidefsky@...ibm.com>
CC: <npiggin@...il.com>, <will.deacon@....com>, <mingo@...nel.org>,
<torvalds@...ux-foundation.org>, <akpm@...ux-foundation.org>,
<luto@...nel.org>, <bp@...en8.de>, Marc Zyngier <maz@...nel.org>,
<linux-arm-kernel@...ts.infradead.org>,
<linux-kernel@...r.kernel.org>, <linux-arch@...r.kernel.org>,
<arm@...nel.org>, <xiexiangyou@...wei.com>
Subject: Re: [RFC][Qusetion] the value of cleared_(ptes|pmds|puds|p4ds) in
struct mmu_gather
Hi Peter,
On 2020/3/30 20:16, Peter Zijlstra wrote:
> On Sat, Mar 28, 2020 at 12:30:50PM +0800, Zhenyu Ye wrote:
>> Hi all,
>>
>> commit a6d60245 "Track which levels of the page tables have been cleared"
>> added cleared_(ptes|pmds|puds|p4ds) in struct mmu_gather, and the values
>> of them are set in some places. For example:
>>
>> In include/asm-generic/tlb.h, pte_free_tlb() set the tlb->cleared_pmds:
>> ---8<---
>> #ifndef pte_free_tlb
>> #define pte_free_tlb(tlb, ptep, address) \
>> do { \
>> __tlb_adjust_range(tlb, address, PAGE_SIZE); \
>> tlb->freed_tables = 1; \
>> tlb->cleared_pmds = 1; \
>> __pte_free_tlb(tlb, ptep, address); \
>> } while (0)
>> #endif
>> ---8<---
>>
>>
>> However, in arch/s390/include/asm/tlb.h, pte_free_tlb() set the tlb->cleared_ptes:
>> ---8<---
>> static inline void pte_free_tlb(struct mmu_gather *tlb, pgtable_t pte,
>> unsigned long address)
>> {
>> __tlb_adjust_range(tlb, address, PAGE_SIZE);
>> tlb->mm->context.flush_mm = 1;
>> tlb->freed_tables = 1;
>> tlb->cleared_ptes = 1;
>> /*
>> * page_table_free_rcu takes care of the allocation bit masks
>> * of the 2K table fragments in the 4K page table page,
>> * then calls tlb_remove_table.
>> */
>> page_table_free_rcu(tlb, (unsigned long *) pte, address);
>> }
>> ---8<---
>>
>>
>> In my view, the cleared_(ptes|pmds|puds) and (pte|pmd|pud)_free_tlb
>> correspond one-to-one. So we should set cleared_ptes in pte_free_tlb(),
>> then use it when needed.
>
> So pte_free_tlb() clears a table of PTE entries, or a PMD level entity,
> also see free_pte_range(). So the generic code makes sense to me. The
> PTE level invalidations will have happened on tlb_remove_tlb_entry().
>
Thanks for your explanation. I can understand now.
>> I'm very confused about this. Which is wrong? Or is there something
>> I understand wrong?
>
> I agree the s390 case is puzzling, Martin does s390 need a PTE level
> invalidate for removing a PTE table or was this a mistake?
>
Then we should wait for @ Martin's reply. Though s390 has never used
this value, I think we still should correct it if this is a mistake.
Thanks,
Zhenyu
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