| Message ID | 20230612210423.18611-4-vishal.moola@gmail.com (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | Split ptdesc from struct page | expand |
On Mon, Jun 12, 2023 at 02:03:52PM -0700, Vishal Moola (Oracle) wrote: > s390 currently uses _refcount to identify fragmented page tables. > The page table struct already has a member pt_frag_refcount used by > powerpc, so have s390 use that instead of the _refcount field as well. > This improves the safety for _refcount and the page table tracking. > > This also allows us to simplify the tracking since we can once again use > the lower byte of pt_frag_refcount instead of the upper byte of _refcount. > > Signed-off-by: Vishal Moola (Oracle) <vishal.moola@gmail.com> One nit below, otherwise Acked-by: Mike Rapoport (IBM) <rppt@kernel.org> > --- > arch/s390/mm/pgalloc.c | 38 +++++++++++++++----------------------- > 1 file changed, 15 insertions(+), 23 deletions(-) > > diff --git a/arch/s390/mm/pgalloc.c b/arch/s390/mm/pgalloc.c > index 66ab68db9842..6b99932abc66 100644 > --- a/arch/s390/mm/pgalloc.c > +++ b/arch/s390/mm/pgalloc.c > @@ -182,20 +182,17 @@ void page_table_free_pgste(struct page *page) > * As follows from the above, no unallocated or fully allocated parent > * pages are contained in mm_context_t::pgtable_list. > * > - * The upper byte (bits 24-31) of the parent page _refcount is used > + * The lower byte (bits 0-7) of the parent page pt_frag_refcount is used > * for tracking contained 2KB-pgtables and has the following format: > * > * PP AA > - * 01234567 upper byte (bits 24-31) of struct page::_refcount > + * 01234567 upper byte (bits 0-7) of struct page::pt_frag_refcount Nit: lower > * || || > * || |+--- upper 2KB-pgtable is allocated > * || +---- lower 2KB-pgtable is allocated > * |+------- upper 2KB-pgtable is pending for removal > * +-------- lower 2KB-pgtable is pending for removal > * > - * (See commit 620b4e903179 ("s390: use _refcount for pgtables") on why > - * using _refcount is possible). > - * > * When 2KB-pgtable is allocated the corresponding AA bit is set to 1. > * The parent page is either: > * - added to mm_context_t::pgtable_list in case the second half of the > @@ -243,11 +240,12 @@ unsigned long *page_table_alloc(struct mm_struct *mm) > if (!list_empty(&mm->context.pgtable_list)) { > page = list_first_entry(&mm->context.pgtable_list, > struct page, lru); > - mask = atomic_read(&page->_refcount) >> 24; > + mask = atomic_read(&page->pt_frag_refcount); > /* > * The pending removal bits must also be checked. > * Failure to do so might lead to an impossible > - * value of (i.e 0x13 or 0x23) written to _refcount. > + * value of (i.e 0x13 or 0x23) written to > + * pt_frag_refcount. > * Such values violate the assumption that pending and > * allocation bits are mutually exclusive, and the rest > * of the code unrails as result. That could lead to > @@ -259,8 +257,8 @@ unsigned long *page_table_alloc(struct mm_struct *mm) > bit = mask & 1; /* =1 -> second 2K */ > if (bit) > table += PTRS_PER_PTE; > - atomic_xor_bits(&page->_refcount, > - 0x01U << (bit + 24)); > + atomic_xor_bits(&page->pt_frag_refcount, > + 0x01U << bit); > list_del(&page->lru); > } > } > @@ -281,12 +279,12 @@ unsigned long *page_table_alloc(struct mm_struct *mm) > table = (unsigned long *) page_to_virt(page); > if (mm_alloc_pgste(mm)) { > /* Return 4K page table with PGSTEs */ > - atomic_xor_bits(&page->_refcount, 0x03U << 24); > + atomic_xor_bits(&page->pt_frag_refcount, 0x03U); > memset64((u64 *)table, _PAGE_INVALID, PTRS_PER_PTE); > memset64((u64 *)table + PTRS_PER_PTE, 0, PTRS_PER_PTE); > } else { > /* Return the first 2K fragment of the page */ > - atomic_xor_bits(&page->_refcount, 0x01U << 24); > + atomic_xor_bits(&page->pt_frag_refcount, 0x01U); > memset64((u64 *)table, _PAGE_INVALID, 2 * PTRS_PER_PTE); > spin_lock_bh(&mm->context.lock); > list_add(&page->lru, &mm->context.pgtable_list); > @@ -323,22 +321,19 @@ void page_table_free(struct mm_struct *mm, unsigned long *table) > * will happen outside of the critical section from this > * function or from __tlb_remove_table() > */ > - mask = atomic_xor_bits(&page->_refcount, 0x11U << (bit + 24)); > - mask >>= 24; > + mask = atomic_xor_bits(&page->pt_frag_refcount, 0x11U << bit); > if (mask & 0x03U) > list_add(&page->lru, &mm->context.pgtable_list); > else > list_del(&page->lru); > spin_unlock_bh(&mm->context.lock); > - mask = atomic_xor_bits(&page->_refcount, 0x10U << (bit + 24)); > - mask >>= 24; > + mask = atomic_xor_bits(&page->pt_frag_refcount, 0x10U << bit); > if (mask != 0x00U) > return; > half = 0x01U << bit; > } else { > half = 0x03U; > - mask = atomic_xor_bits(&page->_refcount, 0x03U << 24); > - mask >>= 24; > + mask = atomic_xor_bits(&page->pt_frag_refcount, 0x03U); > } > > page_table_release_check(page, table, half, mask); > @@ -368,8 +363,7 @@ void page_table_free_rcu(struct mmu_gather *tlb, unsigned long *table, > * outside of the critical section from __tlb_remove_table() or from > * page_table_free() > */ > - mask = atomic_xor_bits(&page->_refcount, 0x11U << (bit + 24)); > - mask >>= 24; > + mask = atomic_xor_bits(&page->pt_frag_refcount, 0x11U << bit); > if (mask & 0x03U) > list_add_tail(&page->lru, &mm->context.pgtable_list); > else > @@ -391,14 +385,12 @@ void __tlb_remove_table(void *_table) > return; > case 0x01U: /* lower 2K of a 4K page table */ > case 0x02U: /* higher 2K of a 4K page table */ > - mask = atomic_xor_bits(&page->_refcount, mask << (4 + 24)); > - mask >>= 24; > + mask = atomic_xor_bits(&page->pt_frag_refcount, mask << 4); > if (mask != 0x00U) > return; > break; > case 0x03U: /* 4K page table with pgstes */ > - mask = atomic_xor_bits(&page->_refcount, 0x03U << 24); > - mask >>= 24; > + mask = atomic_xor_bits(&page->pt_frag_refcount, 0x03U); > break; > } > > -- > 2.40.1 > >
diff --git a/arch/s390/mm/pgalloc.c b/arch/s390/mm/pgalloc.c index 66ab68db9842..6b99932abc66 100644 --- a/arch/s390/mm/pgalloc.c +++ b/arch/s390/mm/pgalloc.c @@ -182,20 +182,17 @@ void page_table_free_pgste(struct page *page) * As follows from the above, no unallocated or fully allocated parent * pages are contained in mm_context_t::pgtable_list. * - * The upper byte (bits 24-31) of the parent page _refcount is used + * The lower byte (bits 0-7) of the parent page pt_frag_refcount is used * for tracking contained 2KB-pgtables and has the following format: * * PP AA - * 01234567 upper byte (bits 24-31) of struct page::_refcount + * 01234567 upper byte (bits 0-7) of struct page::pt_frag_refcount * || || * || |+--- upper 2KB-pgtable is allocated * || +---- lower 2KB-pgtable is allocated * |+------- upper 2KB-pgtable is pending for removal * +-------- lower 2KB-pgtable is pending for removal * - * (See commit 620b4e903179 ("s390: use _refcount for pgtables") on why - * using _refcount is possible). - * * When 2KB-pgtable is allocated the corresponding AA bit is set to 1. * The parent page is either: * - added to mm_context_t::pgtable_list in case the second half of the @@ -243,11 +240,12 @@ unsigned long *page_table_alloc(struct mm_struct *mm) if (!list_empty(&mm->context.pgtable_list)) { page = list_first_entry(&mm->context.pgtable_list, struct page, lru); - mask = atomic_read(&page->_refcount) >> 24; + mask = atomic_read(&page->pt_frag_refcount); /* * The pending removal bits must also be checked. * Failure to do so might lead to an impossible - * value of (i.e 0x13 or 0x23) written to _refcount. + * value of (i.e 0x13 or 0x23) written to + * pt_frag_refcount. * Such values violate the assumption that pending and * allocation bits are mutually exclusive, and the rest * of the code unrails as result. That could lead to @@ -259,8 +257,8 @@ unsigned long *page_table_alloc(struct mm_struct *mm) bit = mask & 1; /* =1 -> second 2K */ if (bit) table += PTRS_PER_PTE; - atomic_xor_bits(&page->_refcount, - 0x01U << (bit + 24)); + atomic_xor_bits(&page->pt_frag_refcount, + 0x01U << bit); list_del(&page->lru); } } @@ -281,12 +279,12 @@ unsigned long *page_table_alloc(struct mm_struct *mm) table = (unsigned long *) page_to_virt(page); if (mm_alloc_pgste(mm)) { /* Return 4K page table with PGSTEs */ - atomic_xor_bits(&page->_refcount, 0x03U << 24); + atomic_xor_bits(&page->pt_frag_refcount, 0x03U); memset64((u64 *)table, _PAGE_INVALID, PTRS_PER_PTE); memset64((u64 *)table + PTRS_PER_PTE, 0, PTRS_PER_PTE); } else { /* Return the first 2K fragment of the page */ - atomic_xor_bits(&page->_refcount, 0x01U << 24); + atomic_xor_bits(&page->pt_frag_refcount, 0x01U); memset64((u64 *)table, _PAGE_INVALID, 2 * PTRS_PER_PTE); spin_lock_bh(&mm->context.lock); list_add(&page->lru, &mm->context.pgtable_list); @@ -323,22 +321,19 @@ void page_table_free(struct mm_struct *mm, unsigned long *table) * will happen outside of the critical section from this * function or from __tlb_remove_table() */ - mask = atomic_xor_bits(&page->_refcount, 0x11U << (bit + 24)); - mask >>= 24; + mask = atomic_xor_bits(&page->pt_frag_refcount, 0x11U << bit); if (mask & 0x03U) list_add(&page->lru, &mm->context.pgtable_list); else list_del(&page->lru); spin_unlock_bh(&mm->context.lock); - mask = atomic_xor_bits(&page->_refcount, 0x10U << (bit + 24)); - mask >>= 24; + mask = atomic_xor_bits(&page->pt_frag_refcount, 0x10U << bit); if (mask != 0x00U) return; half = 0x01U << bit; } else { half = 0x03U; - mask = atomic_xor_bits(&page->_refcount, 0x03U << 24); - mask >>= 24; + mask = atomic_xor_bits(&page->pt_frag_refcount, 0x03U); } page_table_release_check(page, table, half, mask); @@ -368,8 +363,7 @@ void page_table_free_rcu(struct mmu_gather *tlb, unsigned long *table, * outside of the critical section from __tlb_remove_table() or from * page_table_free() */ - mask = atomic_xor_bits(&page->_refcount, 0x11U << (bit + 24)); - mask >>= 24; + mask = atomic_xor_bits(&page->pt_frag_refcount, 0x11U << bit); if (mask & 0x03U) list_add_tail(&page->lru, &mm->context.pgtable_list); else @@ -391,14 +385,12 @@ void __tlb_remove_table(void *_table) return; case 0x01U: /* lower 2K of a 4K page table */ case 0x02U: /* higher 2K of a 4K page table */ - mask = atomic_xor_bits(&page->_refcount, mask << (4 + 24)); - mask >>= 24; + mask = atomic_xor_bits(&page->pt_frag_refcount, mask << 4); if (mask != 0x00U) return; break; case 0x03U: /* 4K page table with pgstes */ - mask = atomic_xor_bits(&page->_refcount, 0x03U << 24); - mask >>= 24; + mask = atomic_xor_bits(&page->pt_frag_refcount, 0x03U); break; }
s390 currently uses _refcount to identify fragmented page tables. The page table struct already has a member pt_frag_refcount used by powerpc, so have s390 use that instead of the _refcount field as well. This improves the safety for _refcount and the page table tracking. This also allows us to simplify the tracking since we can once again use the lower byte of pt_frag_refcount instead of the upper byte of _refcount. Signed-off-by: Vishal Moola (Oracle) <vishal.moola@gmail.com> --- arch/s390/mm/pgalloc.c | 38 +++++++++++++++----------------------- 1 file changed, 15 insertions(+), 23 deletions(-)