powerpc/mm: Don't kmap_atomic() in pte_offset_map() on PPC32 (6453f9ed) · Commits · 戴 / test

On PPC32, pte_offset_map() does a kmap_atomic() in order to support page tables allocated in high memory, just like ARM and x86/32. But since at least 2008 and commit ("powerpc: Remove dead CONFIG_HIGHPTE"), page tables are never allocated in high memory. When the page is in low mem, kmap_atomic() just returns the page address but still disable preemption and pagefault. And it is not an inlined function, so we suffer function call for no reason. Make pte_offset_map() the same as pte_offset_kernel() and make pte_unmap() void, in the same way as PPC64 which doesn't have HIGHMEM. Signed-off-by:

Christophe Leroy <christophe.leroy@c-s.fr> Signed-off-by:

Michael Ellerman <mpe@ellerman.id.au> Link: https://lore.kernel.org/r/03c97f0f6b3790d164822563be80f2fd4713a955.1581932480.git.christophe.leroy@c-s.fr

arch/powerpc/include/asm/book3s/32/pgtable.h

+2 −4

Original line number	Diff line number	Diff line
		@@ -366,10 +366,8 @@ static inline void __ptep_set_access_flags(struct vm_area_struct *vma,
		(((address) >> PAGE_SHIFT) & (PTRS_PER_PTE - 1))
		#define pte_offset_kernel(dir, addr) \
		((pte_t ) pmd_page_vaddr((dir)) + pte_index(addr))
		#define pte_offset_map(dir, addr) \
		((pte_t )(kmap_atomic(pmd_page((dir))) + \
		(pmd_page_vaddr(*(dir)) & ~PAGE_MASK)) + pte_index(addr))
		#define pte_unmap(pte) kunmap_atomic(pte)
		#define pte_offset_map(dir, addr) pte_offset_kernel((dir), (addr))
		static inline void pte_unmap(pte_t *pte) { }

		/*
		* Encode and decode a swap entry.

arch/powerpc/include/asm/nohash/32/pgtable.h

+2 −4

Original line number	Diff line number	Diff line
		@@ -372,10 +372,8 @@ static inline int pte_young(pte_t pte)
		#define pte_offset_kernel(dir, addr) \
		(pmd_bad((dir)) ? NULL : (pte_t )pmd_page_vaddr(*(dir)) + \
		pte_index(addr))
		#define pte_offset_map(dir, addr) \
		((pte_t )(kmap_atomic(pmd_page((dir))) + \
		(pmd_page_vaddr(*(dir)) & ~PAGE_MASK)) + pte_index(addr))
		#define pte_unmap(pte) kunmap_atomic(pte)
		#define pte_offset_map(dir, addr) pte_offset_kernel((dir), (addr))
		static inline void pte_unmap(pte_t *pte) { }

		/*
		* Encode and decode a swap entry.

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