linux-kernel - Re: [PATCH v2 2/3] arm64: mm: HVO: support BBM of vmemmap pgtable safely

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Date: Wed, 20 Dec 2023 21:37:52 +0800
From: Nanyong Sun <sunnanyong@...wei.com>
To: Muchun Song <muchun.song@...ux.dev>
CC: Catalin Marinas <catalin.marinas@....com>, Will Deacon <will@...nel.org>,
	Mike Kravetz <mike.kravetz@...cle.com>, Andrew Morton
	<akpm@...ux-foundation.org>, Anshuman Khandual <anshuman.khandual@....com>,
	"Matthew Wilcox (Oracle)" <willy@...radead.org>, Kefeng Wang
	<wangkefeng.wang@...wei.com>, <linux-arm-kernel@...ts.infradead.org>, LKML
	<linux-kernel@...r.kernel.org>, Linux-MM <linux-mm@...ck.org>
Subject: Re: [PATCH v2 2/3] arm64: mm: HVO: support BBM of vmemmap pgtable
 safely

On 2023/12/20 14:32, Muchun Song wrote:

>
>> On Dec 20, 2023, at 13:18, Nanyong Sun <sunnanyong@...wei.com> wrote:
>>
>> Implement vmemmap_update_pmd and vmemmap_update_pte on arm64 to do
>> BBM(break-before-make) logic when change the page table of vmemmap
>> address, they will under the init_mm.page_table_lock.
>> If a translation fault of vmemmap address concurrently happened after
>> pte/pmd cleared, vmemmap page fault handler will acquire the
>> init_mm.page_table_lock to wait for vmemmap update to complete,
>> by then the virtual address is valid again, so PF can return and
>> access can continue.
>> In other case, do the traditional kernel fault.
>>
>> Implement vmemmap_flush_tlb_all/range on arm64 with nothing
>> to do because tlb already flushed in every single BBM.
>>
>> Signed-off-by: Nanyong Sun <sunnanyong@...wei.com>
>> ---
>> arch/arm64/include/asm/esr.h |  4 ++
>> arch/arm64/include/asm/mmu.h | 20 +++++++++
>> arch/arm64/mm/fault.c        | 78 ++++++++++++++++++++++++++++++++++--
>> arch/arm64/mm/mmu.c          | 28 +++++++++++++
>> 4 files changed, 127 insertions(+), 3 deletions(-)
>>
>> diff --git a/arch/arm64/include/asm/esr.h b/arch/arm64/include/asm/esr.h
>> index ae35939f395b..1c63256efd25 100644
>> --- a/arch/arm64/include/asm/esr.h
>> +++ b/arch/arm64/include/asm/esr.h
>> @@ -116,6 +116,10 @@
>> #define ESR_ELx_FSC_SERROR (0x11)
>> #define ESR_ELx_FSC_ACCESS (0x08)
>> #define ESR_ELx_FSC_FAULT (0x04)
>> +#define ESR_ELx_FSC_FAULT_L0    (0x04)
>> +#define ESR_ELx_FSC_FAULT_L1    (0x05)
>> +#define ESR_ELx_FSC_FAULT_L2    (0x06)
>> +#define ESR_ELx_FSC_FAULT_L3    (0x07)
>> #define ESR_ELx_FSC_PERM (0x0C)
>> #define ESR_ELx_FSC_SEA_TTW0 (0x14)
>> #define ESR_ELx_FSC_SEA_TTW1 (0x15)
>> diff --git a/arch/arm64/include/asm/mmu.h b/arch/arm64/include/asm/mmu.h
>> index 2fcf51231d6e..b553bc37c925 100644
>> --- a/arch/arm64/include/asm/mmu.h
>> +++ b/arch/arm64/include/asm/mmu.h
>> @@ -76,5 +76,25 @@ extern bool kaslr_requires_kpti(void);
>> #define INIT_MM_CONTEXT(name) \
>> .pgd = init_pg_dir,
>>
>> +#ifdef CONFIG_HUGETLB_PAGE_OPTIMIZE_VMEMMAP
>> +void vmemmap_update_pmd(unsigned long addr, pmd_t *pmdp, pte_t *ptep);
>> +#define vmemmap_update_pmd vmemmap_update_pmd
>> +void vmemmap_update_pte(unsigned long addr, pte_t *ptep, pte_t pte);
>> +#define vmemmap_update_pte vmemmap_update_pte
>> +
>> +static inline void vmemmap_flush_tlb_all(void)
>> +{
>> + 	/* do nothing, already flushed tlb in every single BBM */
>> +}
>> +#define vmemmap_flush_tlb_all vmemmap_flush_tlb_all
>> +
>> +static inline void vmemmap_flush_tlb_range(unsigned long start,
>> +   unsigned long end)
>> +{
>> + 	/* do nothing, already flushed tlb in every single BBM */
>> +}
>> +#define vmemmap_flush_tlb_range vmemmap_flush_tlb_range
>> +#endif
> I think those declaration related to TLB flushing should be moved
> to arch/arm64/include/asm/tlbflush.h since we do not include
> <asm/mmu.h> explicitly in hugetlb_vmemmap.c and its functionality
> is to flush TLB. Luckily, <asm/tlbflush.h> is included by hugetlb_vmemmap.c.
>
> Additionally, vmemmap_update_pmd/pte helpers should be moved to
> arch/arm64/include/asm/pgtable.h since it is really pgtable related
> operations.
>
> Thanks.

Yes，I will move them in next version.

Thanks for your time.

>
>
>
>
> .