From mboxrd@z Thu Jan 1 00:00:00 1970 From: Yu-cheng Yu Subject: [RFC PATCH v9 6/7] mm: Update alloc_set_pte() for zero page Date: Wed, 5 Feb 2020 10:23:07 -0800 Message-ID: <20200205182308.4028-7-yu-cheng.yu@intel.com> References: <20200205182308.4028-1-yu-cheng.yu@intel.com> Mime-Version: 1.0 Content-Transfer-Encoding: 8bit Return-path: In-Reply-To: <20200205182308.4028-1-yu-cheng.yu@intel.com> Sender: linux-kernel-owner@vger.kernel.org To: x86@kernel.org, "H. Peter Anvin" , Thomas Gleixner , Ingo Molnar , linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org, linux-mm@kvack.org, linux-arch@vger.kernel.org, linux-api@vger.kernel.org, Arnd Bergmann , Andy Lutomirski , Balbir Singh , Borislav Petkov , Cyrill Gorcunov , Dave Hansen , Eugene Syromiatnikov , Florian Weimer , "H.J. Lu" , Jann Horn , Jonathan Corbet , Kees Cook , Mike Kravetz , Nadav Amit Cc: Yu-cheng Yu List-Id: linux-api@vger.kernel.org Update alloc_set_pte() for the zero-page case. A special mapping can also use a zero page for read. One use case is the Indirect Branch Tracking legacy code page (introduced next). Signed-off-by: Yu-cheng Yu --- mm/memory.c | 8 ++++++++ 1 file changed, 8 insertions(+) diff --git a/mm/memory.c b/mm/memory.c index 6daa28614327..58c1e4b60991 100644 --- a/mm/memory.c +++ b/mm/memory.c @@ -3447,6 +3447,12 @@ vm_fault_t alloc_set_pte(struct vm_fault *vmf, struct mem_cgroup *memcg, flush_icache_page(vma, page); entry = mk_pte(page, vma->vm_page_prot); + + if (is_zero_pfn(pte_pfn(entry))) { + entry = pte_mkspecial(entry); + goto alloc_set_pte_out; + } + if (write) entry = maybe_mkwrite(pte_mkdirty(entry), vma); /* copy-on-write page */ @@ -3459,6 +3465,8 @@ vm_fault_t alloc_set_pte(struct vm_fault *vmf, struct mem_cgroup *memcg, inc_mm_counter_fast(vma->vm_mm, mm_counter_file(page)); page_add_file_rmap(page, false); } + +alloc_set_pte_out: set_pte_at(vma->vm_mm, vmf->address, vmf->pte, entry); /* no need to invalidate: a not-present page won't be cached */ -- 2.21.0