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riscv: mm: Implement pmdp_collapse_flush for THP 

When THP is enabled, 4K pages are collapsed into a single huge
page using the generic pmdp_collapse_flush() which will further
use flush_tlb_range() to shoot-down stale TLB entries. Unfortunately,
the generic pmdp_collapse_flush() only invalidates cached leaf PTEs
using address specific SFENCEs which results in repetitive (or
unpredictable) page faults on RISC-V implementations which cache
non-leaf PTEs.

Provide a RISC-V specific pmdp_collapse_flush() which ensures both
cached leaf and non-leaf PTEs are invalidated by using non-address
specific SFENCEs as recommended by the RISC-V privileged specification.

Fixes: e88b333142 ("riscv: mm: add THP support on 64-bit")
Signed-off-by: Mayuresh Chitale <mchitale@ventanamicro.com>
Link: https://lore.kernel.org/r/20230130074815.1694055-1-mchitale@ventanamicro.com
Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>
This commit is contained in:
Mayuresh Chitale 2023-01-30 13:18:15 +05:30 committed by Palmer Dabbelt
parent 2f394c0e7d
commit f0293cd1f4
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2 changed files with 24 additions and 0 deletions
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4
arch/riscv/include/asm/pgtable.h
View File

@ -721,6 +721,10 @@ static inline pmd_t pmdp_establish(struct vm_area_struct *vma,
page_table_check_pmd_set(vma->vm_mm, address, pmdp, pmd);
return __pmd(atomic_long_xchg((atomic_long_t *)pmdp, pmd_val(pmd)));
}
#define pmdp_collapse_flush pmdp_collapse_flush
extern pmd_t pmdp_collapse_flush(struct vm_area_struct *vma,
unsigned long address, pmd_t *pmdp);
#endif /* CONFIG_TRANSPARENT_HUGEPAGE */
/*

20
arch/riscv/mm/pgtable.c
View File

@ -81,3 +81,23 @@ int pmd_free_pte_page(pmd_t *pmd, unsigned long addr)
}
#endif /* CONFIG_HAVE_ARCH_HUGE_VMAP */
#ifdef CONFIG_TRANSPARENT_HUGEPAGE
pmd_t pmdp_collapse_flush(struct vm_area_struct *vma,
unsigned long address, pmd_t *pmdp)
{
pmd_t pmd = pmdp_huge_get_and_clear(vma->vm_mm, address, pmdp);
VM_BUG_ON(address & ~HPAGE_PMD_MASK);
VM_BUG_ON(pmd_trans_huge(*pmdp));
/*
* When leaf PTE entries (regular pages) are collapsed into a leaf
* PMD entry (huge page), a valid non-leaf PTE is converted into a
* valid leaf PTE at the level 1 page table. Since the sfence.vma
* forms that specify an address only apply to leaf PTEs, we need a
* global flush here. collapse_huge_page() assumes these flushes are
* eager, so just do the fence here.
*/
flush_tlb_mm(vma->vm_mm);
return pmd;
}
#endif /* CONFIG_TRANSPARENT_HUGEPAGE */