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4239c198e8
To support fast gup, the commit 69be3fb111 ("riscv: enable
MMU_GATHER_RCU_TABLE_FREE for SMP && MMU") did the following:
1) use tlb_remove_page_ptdesc() for those platforms which use IPI to
perform TLB shootdown
2) use tlb_remove_ptdesc() for those platforms which use SBI to perform
TLB shootdown
The tlb_remove_page_ptdesc() is the wrapper of the tlb_remove_page(). By
design, the tlb_remove_page() should be used to remove a normal page from
a page table entry, and should not be used for page table pages.
The tlb_remove_ptdesc() is the wrapper of the tlb_remove_table(), which is
designed specifically for freeing page table pages. If the
CONFIG_MMU_GATHER_TABLE_FREE is enabled, the tlb_remove_table() will use
semi RCU to free page table pages, that is:
- batch table freeing: asynchronous free by RCU
- single table freeing: IPI + synchronous free
If the CONFIG_MMU_GATHER_TABLE_FREE is disabled, the tlb_remove_table()
will fall back to pagetable_dtor() + tlb_remove_page().
For case 1), since we need to perform TLB shootdown before freeing the
page table page, the local_irq_save() in fast gup can block the freeing
and protect the fast gup page walker. Therefore we can ensure safety by
just using tlb_remove_page_ptdesc(). In addition, we can also the
tlb_remove_ptdesc()/tlb_remove_table() to achieve it, and it doesn't
matter whether CONFIG_MMU_GATHER_RCU_TABLE_FREE is selected. And in
theory, the performance of freeing pages asynchronously via RCU will not
be lower than synchronous free.
For case 2), since local_irq_save() only disable S-privilege IPI irq but
not M-privilege's, which is used by the SBI implementation to perform TLB
shootdown, so we must select CONFIG_MMU_GATHER_RCU_TABLE_FREE and use
tlb_remove_ptdesc() to ensure safety. The riscv selects this config for
SMP && MMU, the CONFIG_RISCV_SBI is dependent on MMU. Therefore, only the
UP system may have the situation where CONFIG_MMU_GATHER_RCU_TABLE_FREE is
disabled but CONFIG_RISCV_SBI is enabled. But there is no freeing vs fast
gup race in the UP system.
So, in summary, we can use tlb_remove_ptdesc() to support fast gup in all
cases, and this interface is specifically designed for page table pages.
So let's use it unconditionally.
Link: https://lkml.kernel.org/r/9025595e895515515c95e48db54b29afa489c41d.1740454179.git.zhengqi.arch@bytedance.com
Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com>
Suggested-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Alexandre Ghiti <alexghiti@rivosinc.com>
Cc: "Aneesh Kumar K.V" <aneesh.kumar@kernel.org>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Hugh Dickens <hughd@google.com>
Cc: Jann Horn <jannh@google.com>
Cc: Kevin Brodsky <kevin.brodsky@arm.com>
Cc: Matthew Wilcow (Oracle) <willy@infradead.org>
Cc: "Mike Rapoport (IBM)" <rppt@kernel.org>
Cc: Muchun Song <muchun.song@linux.dev>
Cc: Nicholas Piggin <npiggin@gmail.com>
Cc: Rik van Riel <riel@surriel.com>
Cc: Vishal Moola (Oracle) <vishal.moola@gmail.com>
Cc: Will Deacon <will@kernel.org>
Cc: Yu Zhao <yuzhao@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
140 lines
3.2 KiB
C
140 lines
3.2 KiB
C
/* SPDX-License-Identifier: GPL-2.0-only */
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/*
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* Copyright (C) 2009 Chen Liqin <liqin.chen@sunplusct.com>
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* Copyright (C) 2012 Regents of the University of California
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*/
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#ifndef _ASM_RISCV_PGALLOC_H
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#define _ASM_RISCV_PGALLOC_H
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#include <linux/mm.h>
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#include <asm/sbi.h>
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#include <asm/tlb.h>
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#ifdef CONFIG_MMU
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#define __HAVE_ARCH_PUD_FREE
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#include <asm-generic/pgalloc.h>
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static inline void pmd_populate_kernel(struct mm_struct *mm,
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pmd_t *pmd, pte_t *pte)
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{
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unsigned long pfn = virt_to_pfn(pte);
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set_pmd(pmd, __pmd((pfn << _PAGE_PFN_SHIFT) | _PAGE_TABLE));
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}
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static inline void pmd_populate(struct mm_struct *mm,
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pmd_t *pmd, pgtable_t pte)
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{
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unsigned long pfn = virt_to_pfn(page_address(pte));
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set_pmd(pmd, __pmd((pfn << _PAGE_PFN_SHIFT) | _PAGE_TABLE));
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}
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#ifndef __PAGETABLE_PMD_FOLDED
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static inline void pud_populate(struct mm_struct *mm, pud_t *pud, pmd_t *pmd)
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{
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unsigned long pfn = virt_to_pfn(pmd);
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set_pud(pud, __pud((pfn << _PAGE_PFN_SHIFT) | _PAGE_TABLE));
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}
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static inline void p4d_populate(struct mm_struct *mm, p4d_t *p4d, pud_t *pud)
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{
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if (pgtable_l4_enabled) {
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unsigned long pfn = virt_to_pfn(pud);
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set_p4d(p4d, __p4d((pfn << _PAGE_PFN_SHIFT) | _PAGE_TABLE));
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}
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}
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static inline void p4d_populate_safe(struct mm_struct *mm, p4d_t *p4d,
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pud_t *pud)
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{
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if (pgtable_l4_enabled) {
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unsigned long pfn = virt_to_pfn(pud);
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set_p4d_safe(p4d,
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__p4d((pfn << _PAGE_PFN_SHIFT) | _PAGE_TABLE));
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}
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}
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static inline void pgd_populate(struct mm_struct *mm, pgd_t *pgd, p4d_t *p4d)
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{
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if (pgtable_l5_enabled) {
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unsigned long pfn = virt_to_pfn(p4d);
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set_pgd(pgd, __pgd((pfn << _PAGE_PFN_SHIFT) | _PAGE_TABLE));
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}
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}
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static inline void pgd_populate_safe(struct mm_struct *mm, pgd_t *pgd,
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p4d_t *p4d)
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{
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if (pgtable_l5_enabled) {
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unsigned long pfn = virt_to_pfn(p4d);
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set_pgd_safe(pgd,
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__pgd((pfn << _PAGE_PFN_SHIFT) | _PAGE_TABLE));
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}
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}
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#define pud_free pud_free
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static inline void pud_free(struct mm_struct *mm, pud_t *pud)
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{
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if (pgtable_l4_enabled)
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__pud_free(mm, pud);
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}
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static inline void __pud_free_tlb(struct mmu_gather *tlb, pud_t *pud,
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unsigned long addr)
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{
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if (pgtable_l4_enabled)
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tlb_remove_ptdesc(tlb, virt_to_ptdesc(pud));
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}
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static inline void __p4d_free_tlb(struct mmu_gather *tlb, p4d_t *p4d,
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unsigned long addr)
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{
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if (pgtable_l5_enabled)
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tlb_remove_ptdesc(tlb, virt_to_ptdesc(p4d));
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}
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#endif /* __PAGETABLE_PMD_FOLDED */
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static inline void sync_kernel_mappings(pgd_t *pgd)
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{
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memcpy(pgd + USER_PTRS_PER_PGD,
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init_mm.pgd + USER_PTRS_PER_PGD,
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(PTRS_PER_PGD - USER_PTRS_PER_PGD) * sizeof(pgd_t));
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}
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static inline pgd_t *pgd_alloc(struct mm_struct *mm)
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{
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pgd_t *pgd;
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pgd = __pgd_alloc(mm, 0);
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if (likely(pgd != NULL)) {
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/* Copy kernel mappings */
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sync_kernel_mappings(pgd);
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}
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return pgd;
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}
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#ifndef __PAGETABLE_PMD_FOLDED
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static inline void __pmd_free_tlb(struct mmu_gather *tlb, pmd_t *pmd,
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unsigned long addr)
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{
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tlb_remove_ptdesc(tlb, virt_to_ptdesc(pmd));
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}
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#endif /* __PAGETABLE_PMD_FOLDED */
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static inline void __pte_free_tlb(struct mmu_gather *tlb, pgtable_t pte,
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unsigned long addr)
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{
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tlb_remove_ptdesc(tlb, page_ptdesc(pte));
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}
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#endif /* CONFIG_MMU */
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#endif /* _ASM_RISCV_PGALLOC_H */
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