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 14:32:33 +0800
From: Muchun Song <muchun.song@...ux.dev>
To: Nanyong Sun <sunnanyong@...wei.com>
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 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.