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Message-Id: <20210830235927.6443-5-rick.p.edgecombe@intel.com> Date: Mon, 30 Aug 2021 16:59:12 -0700 From: Rick Edgecombe <rick.p.edgecombe@...el.com> To: dave.hansen@...el.com, luto@...nel.org, peterz@...radead.org, x86@...nel.org, akpm@...ux-foundation.org, keescook@...omium.org, shakeelb@...gle.com, vbabka@...e.cz, rppt@...nel.org Cc: Rick Edgecombe <rick.p.edgecombe@...el.com>, linux-mm@...ck.org, linux-hardening@...r.kernel.org, kernel-hardening@...ts.openwall.com, ira.weiny@...el.com, dan.j.williams@...el.com, linux-kernel@...r.kernel.org Subject: [RFC PATCH v2 04/19] mm: Explicitly zero page table lock ptr In ptlock_init() there is a VM_BUG_ON_PAGE() check on the page table lock pointer. Explicitly zero the lock in ptlock_free() so a page table lock can be re-initialized without triggering the BUG_ON(). It appears this doesn't normally trigger because the private field shares the same space in struct page as ptl and page tables always return to the buddy allocator before being re-initialized as new page tables. When the page returns to the buddy allocator, private gets used to store the page order, so it inadvertently clears ptl as well. In future patches, pages will get re-initialized as page tables without returning to the buddy allocator so this is needed. Signed-off-by: Rick Edgecombe <rick.p.edgecombe@...el.com> --- mm/memory.c | 1 + 1 file changed, 1 insertion(+) diff --git a/mm/memory.c b/mm/memory.c index 25fc46e87214..e6d630463c7f 100644 --- a/mm/memory.c +++ b/mm/memory.c @@ -5465,5 +5465,6 @@ bool ptlock_alloc(struct page *page) void ptlock_free(struct page *page) { kmem_cache_free(page_ptl_cachep, page->ptl); + page->ptl = 0; } #endif -- 2.17.1
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