linux-kernel - [RFC PATCH v9 6/7] mm: Update alloc_set

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Date:   Wed,  5 Feb 2020 10:23:07 -0800
From:   Yu-cheng Yu <yu-cheng.yu@...el.com>
To:     x86@...nel.org, "H. Peter Anvin" <hpa@...or.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org,
        linux-doc@...r.kernel.org, linux-mm@...ck.org,
        linux-arch@...r.kernel.org, linux-api@...r.kernel.org,
        Arnd Bergmann <arnd@...db.de>,
        Andy Lutomirski <luto@...nel.org>,
        Balbir Singh <bsingharora@...il.com>,
        Borislav Petkov <bp@...en8.de>,
        Cyrill Gorcunov <gorcunov@...il.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Eugene Syromiatnikov <esyr@...hat.com>,
        Florian Weimer <fweimer@...hat.com>,
        "H.J. Lu" <hjl.tools@...il.com>, Jann Horn <jannh@...gle.com>,
        Jonathan Corbet <corbet@....net>,
        Kees Cook <keescook@...omium.org>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        Nadav Amit <nadav.amit@...il.com>,
        Oleg Nesterov <oleg@...hat.com>, Pavel Machek <pavel@....cz>,
        Peter Zijlstra <peterz@...radead.org>,
        Randy Dunlap <rdunlap@...radead.org>,
        "Ravi V. Shankar" <ravi.v.shankar@...el.com>,
        Vedvyas Shanbhogue <vedvyas.shanbhogue@...el.com>,
        Dave Martin <Dave.Martin@....com>, x86-patch-review@...el.com
Cc:     Yu-cheng Yu <yu-cheng.yu@...el.com>
Subject: [RFC PATCH v9 6/7] mm: Update alloc_set_pte() for zero page

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 <yu-cheng.yu@...el.com>
---
 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