From 645d5ce2f7d6cb4dcf6a4e087fb550e238d24283 Mon Sep 17 00:00:00 2001 From: "Aneesh Kumar K.V" Date: Thu, 9 Jul 2020 18:49:22 +0530 Subject: [PATCH] powerpc/mm/radix: Fix PTE/PMD fragment count for early page table mappings We can hit the following BUG_ON during memory unplug: kernel BUG at arch/powerpc/mm/book3s64/pgtable.c:342! Oops: Exception in kernel mode, sig: 5 [#1] LE PAGE_SIZE=64K MMU=Radix SMP NR_CPUS=2048 NUMA pSeries NIP [c000000000093308] pmd_fragment_free+0x48/0xc0 LR [c00000000147bfec] remove_pagetable+0x578/0x60c Call Trace: 0xc000008050000000 (unreliable) remove_pagetable+0x384/0x60c radix__remove_section_mapping+0x18/0x2c remove_section_mapping+0x1c/0x3c arch_remove_memory+0x11c/0x180 try_remove_memory+0x120/0x1b0 __remove_memory+0x20/0x40 dlpar_remove_lmb+0xc0/0x114 dlpar_memory+0x8b0/0xb20 handle_dlpar_errorlog+0xc0/0x190 pseries_hp_work_fn+0x2c/0x60 process_one_work+0x30c/0x810 worker_thread+0x98/0x540 kthread+0x1c4/0x1d0 ret_from_kernel_thread+0x5c/0x74 This occurs when unplug is attempted for such memory which has been mapped using memblock pages as part of early kernel page table setup. We wouldn't have initialized the PMD or PTE fragment count for those PMD or PTE pages. This can be fixed by allocating memory in PAGE_SIZE granularity during early page table allocation. This makes sure a specific page is not shared for another memblock allocation and we can free them correctly on removing page-table pages. Since we now do PAGE_SIZE allocations for both PUD table and PMD table (Note that PTE table allocation is already of PAGE_SIZE), we end up allocating more memory for the same amount of system RAM. Here is a comparision of how much more we need for a 64T and 2G system after this patch: 1. 64T system ------------- 64T RAM would need 64G for vmemmap with struct page size being 64B. 128 PUD tables for 64T memory (1G mappings) 1 PUD table and 64 PMD tables for 64G vmemmap (2M mappings) With default PUD[PMD]_TABLE_SIZE(4K), (128+1+64)*4K=772K With PAGE_SIZE(64K) table allocations, (128+1+64)*64K=12352K 2. 2G system ------------ 2G RAM would need 2M for vmemmap with struct page size being 64B. 1 PUD table for 2G memory (1G mapping) 1 PUD table and 1 PMD table for 2M vmemmap (2M mappings) With default PUD[PMD]_TABLE_SIZE(4K), (1+1+1)*4K=12K With new PAGE_SIZE(64K) table allocations, (1+1+1)*64K=192K Signed-off-by: Bharata B Rao Signed-off-by: Aneesh Kumar K.V Signed-off-by: Michael Ellerman Link: https://lore.kernel.org/r/20200709131925.922266-2-aneesh.kumar@linux.ibm.com --- arch/powerpc/include/asm/book3s/64/pgalloc.h | 16 +++++++++++++++- arch/powerpc/mm/book3s64/pgtable.c | 5 ++++- arch/powerpc/mm/book3s64/radix_pgtable.c | 15 +++++++++++---- arch/powerpc/mm/pgtable-frag.c | 3 +++ 4 files changed, 33 insertions(+), 6 deletions(-) diff --git a/arch/powerpc/include/asm/book3s/64/pgalloc.h b/arch/powerpc/include/asm/book3s/64/pgalloc.h index 69c5b05..e1af0b3 100644 --- a/arch/powerpc/include/asm/book3s/64/pgalloc.h +++ b/arch/powerpc/include/asm/book3s/64/pgalloc.h @@ -107,9 +107,23 @@ static inline pud_t *pud_alloc_one(struct mm_struct *mm, unsigned long addr) return pud; } +static inline void __pud_free(pud_t *pud) +{ + struct page *page = virt_to_page(pud); + + /* + * Early pud pages allocated via memblock allocator + * can't be directly freed to slab + */ + if (PageReserved(page)) + free_reserved_page(page); + else + kmem_cache_free(PGT_CACHE(PUD_CACHE_INDEX), pud); +} + static inline void pud_free(struct mm_struct *mm, pud_t *pud) { - kmem_cache_free(PGT_CACHE(PUD_CACHE_INDEX), pud); + return __pud_free(pud); } static inline void pud_populate(struct mm_struct *mm, pud_t *pud, pmd_t *pmd) diff --git a/arch/powerpc/mm/book3s64/pgtable.c b/arch/powerpc/mm/book3s64/pgtable.c index c58ad10..85de5b5 100644 --- a/arch/powerpc/mm/book3s64/pgtable.c +++ b/arch/powerpc/mm/book3s64/pgtable.c @@ -339,6 +339,9 @@ void pmd_fragment_free(unsigned long *pmd) { struct page *page = virt_to_page(pmd); + if (PageReserved(page)) + return free_reserved_page(page); + BUG_ON(atomic_read(&page->pt_frag_refcount) <= 0); if (atomic_dec_and_test(&page->pt_frag_refcount)) { pgtable_pmd_page_dtor(page); @@ -356,7 +359,7 @@ static inline void pgtable_free(void *table, int index) pmd_fragment_free(table); break; case PUD_INDEX: - kmem_cache_free(PGT_CACHE(PUD_CACHE_INDEX), table); + __pud_free(table); break; #if defined(CONFIG_PPC_4K_PAGES) && defined(CONFIG_HUGETLB_PAGE) /* 16M hugepd directory at pud level */ diff --git a/arch/powerpc/mm/book3s64/radix_pgtable.c b/arch/powerpc/mm/book3s64/radix_pgtable.c index bb00e0c..85806a6 100644 --- a/arch/powerpc/mm/book3s64/radix_pgtable.c +++ b/arch/powerpc/mm/book3s64/radix_pgtable.c @@ -56,6 +56,13 @@ static __ref void *early_alloc_pgtable(unsigned long size, int nid, return ptr; } +/* + * When allocating pud or pmd pointers, we allocate a complete page + * of PAGE_SIZE rather than PUD_TABLE_SIZE or PMD_TABLE_SIZE. This + * is to ensure that the page obtained from the memblock allocator + * can be completely used as page table page and can be freed + * correctly when the page table entries are removed. + */ static int early_map_kernel_page(unsigned long ea, unsigned long pa, pgprot_t flags, unsigned int map_page_size, @@ -72,8 +79,8 @@ static int early_map_kernel_page(unsigned long ea, unsigned long pa, pgdp = pgd_offset_k(ea); p4dp = p4d_offset(pgdp, ea); if (p4d_none(*p4dp)) { - pudp = early_alloc_pgtable(PUD_TABLE_SIZE, nid, - region_start, region_end); + pudp = early_alloc_pgtable(PAGE_SIZE, nid, + region_start, region_end); p4d_populate(&init_mm, p4dp, pudp); } pudp = pud_offset(p4dp, ea); @@ -82,8 +89,8 @@ static int early_map_kernel_page(unsigned long ea, unsigned long pa, goto set_the_pte; } if (pud_none(*pudp)) { - pmdp = early_alloc_pgtable(PMD_TABLE_SIZE, nid, - region_start, region_end); + pmdp = early_alloc_pgtable(PAGE_SIZE, nid, region_start, + region_end); pud_populate(&init_mm, pudp, pmdp); } pmdp = pmd_offset(pudp, ea); diff --git a/arch/powerpc/mm/pgtable-frag.c b/arch/powerpc/mm/pgtable-frag.c index ee4bd6d..97ae493 100644 --- a/arch/powerpc/mm/pgtable-frag.c +++ b/arch/powerpc/mm/pgtable-frag.c @@ -110,6 +110,9 @@ void pte_fragment_free(unsigned long *table, int kernel) { struct page *page = virt_to_page(table); + if (PageReserved(page)) + return free_reserved_page(page); + BUG_ON(atomic_read(&page->pt_frag_refcount) <= 0); if (atomic_dec_and_test(&page->pt_frag_refcount)) { if (!kernel) -- 2.7.4