From: Minchan Kim Date: Wed, 11 Jan 2017 00:57:51 +0000 (-0800) Subject: mm: pmd dirty emulation in page fault handler X-Git-Url: https://git.karo-electronics.de/?a=commitdiff_plain;h=20f664aabeb88d582b623a625f83b0454fa34f07;p=linux-beck.git mm: pmd dirty emulation in page fault handler Andreas reported [1] made a test in jemalloc hang in THP mode in arm64: http://lkml.kernel.org/r/mvmmvfy37g1.fsf@hawking.suse.de The problem is currently page fault handler doesn't supports dirty bit emulation of pmd for non-HW dirty-bit architecture so that application stucks until VM marked the pmd dirty. How the emulation work depends on the architecture. In case of arm64, when it set up pte firstly, it sets pte PTE_RDONLY to get a chance to mark the pte dirty via triggering page fault when store access happens. Once the page fault occurs, VM marks the pmd dirty and arch code for setting pmd will clear PTE_RDONLY for application to proceed. IOW, if VM doesn't mark the pmd dirty, application hangs forever by repeated fault(i.e., store op but the pmd is PTE_RDONLY). This patch enables pmd dirty-bit emulation for those architectures. [1] b8d3c4c3009d, mm/huge_memory.c: don't split THP page when MADV_FREE syscall is called Fixes: b8d3c4c3009d ("mm/huge_memory.c: don't split THP page when MADV_FREE syscall is called") Link: http://lkml.kernel.org/r/1482506098-6149-1-git-send-email-minchan@kernel.org Signed-off-by: Minchan Kim Reported-by: Andreas Schwab Tested-by: Andreas Schwab Acked-by: Kirill A. Shutemov Acked-by: Michal Hocko Cc: Jason Evans Cc: Will Deacon Cc: Catalin Marinas Cc: [4.5+] Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- diff --git a/mm/huge_memory.c b/mm/huge_memory.c index 72339a646fb1..9a6bd6c8d55a 100644 --- a/mm/huge_memory.c +++ b/mm/huge_memory.c @@ -883,15 +883,17 @@ void huge_pmd_set_accessed(struct vm_fault *vmf, pmd_t orig_pmd) { pmd_t entry; unsigned long haddr; + bool write = vmf->flags & FAULT_FLAG_WRITE; vmf->ptl = pmd_lock(vmf->vma->vm_mm, vmf->pmd); if (unlikely(!pmd_same(*vmf->pmd, orig_pmd))) goto unlock; entry = pmd_mkyoung(orig_pmd); + if (write) + entry = pmd_mkdirty(entry); haddr = vmf->address & HPAGE_PMD_MASK; - if (pmdp_set_access_flags(vmf->vma, haddr, vmf->pmd, entry, - vmf->flags & FAULT_FLAG_WRITE)) + if (pmdp_set_access_flags(vmf->vma, haddr, vmf->pmd, entry, write)) update_mmu_cache_pmd(vmf->vma, vmf->address, vmf->pmd); unlock: