linux-kernel - [PATCH] x86-64: Do not allocate memory for the vDSO

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Message-Id: <2c4ed5c2c2e93603790229e0c3403ae506ccc0cb.1311277573.git.luto@mit.edu>
Date:	Thu, 21 Jul 2011 15:47:10 -0400
From:	Andy Lutomirski <luto@....EDU>
To:	mingo@...hat.com, wzt <wzt.wzt@...il.com>
Cc:	linux-kernel@...r.kernel.org, x86@...nel.org, ak@...ux.intel.com,
	tglx@...utronix.de, hpa@...or.com, Michal Hocko <mhocko@...e.cz>,
	Andy Lutomirski <luto@....edu>
Subject: [PATCH] x86-64: Do not allocate memory for the vDSO

We can map the vDSO straight from kernel data, saving a few page
allocations.  As an added bonus, the deleted code contained a memory
leak.

Signed-off-by: Andy Lutomirski <luto@....edu>
---
 arch/x86/vdso/vdso.S |   15 +++++++++++++--
 arch/x86/vdso/vma.c  |   25 ++++++-------------------
 2 files changed, 19 insertions(+), 21 deletions(-)

diff --git a/arch/x86/vdso/vdso.S b/arch/x86/vdso/vdso.S
index 1d3aa6b..1b979c1 100644
--- a/arch/x86/vdso/vdso.S
+++ b/arch/x86/vdso/vdso.S
@@ -1,10 +1,21 @@
+#include <asm/page_types.h>
+#include <linux/linkage.h>
 #include <linux/init.h>
 
-__INITDATA
+__PAGE_ALIGNED_DATA
 
 	.globl vdso_start, vdso_end
+	.align PAGE_SIZE
 vdso_start:
 	.incbin "arch/x86/vdso/vdso.so"
 vdso_end:
 
-__FINIT
+.previous
+
+	.globl vdso_pages
+	.bss
+	.align 8
+	.type vdso_pages, @object
+vdso_pages:
+	.zero (vdso_end - vdso_start + PAGE_SIZE - 1) / PAGE_SIZE * 8
+	.size vdso_pages, .-vdso_pages
diff --git a/arch/x86/vdso/vma.c b/arch/x86/vdso/vma.c
index ba92244..40e4cb0 100644
--- a/arch/x86/vdso/vma.c
+++ b/arch/x86/vdso/vma.c
@@ -14,13 +14,14 @@
 #include <asm/vgtod.h>
 #include <asm/proto.h>
 #include <asm/vdso.h>
+#include <asm/page.h>
 
 unsigned int __read_mostly vdso_enabled = 1;
 
 extern char vdso_start[], vdso_end[];
 extern unsigned short vdso_sync_cpuid;
 
-static struct page **vdso_pages;
+extern struct page *vdso_pages[];
 static unsigned vdso_size;
 
 static void patch_vdso(void *vdso, size_t len)
@@ -51,7 +52,7 @@ found:
 	apply_alternatives(alt_data, alt_data + alt_sec->sh_size);
 }
 
-static int __init init_vdso_vars(void)
+static int __init init_vdso(void)
 {
 	int npages = (vdso_end - vdso_start + PAGE_SIZE - 1) / PAGE_SIZE;
 	int i;
@@ -59,26 +60,12 @@ static int __init init_vdso_vars(void)
 	patch_vdso(vdso_start, vdso_end - vdso_start);
 
 	vdso_size = npages << PAGE_SHIFT;
-	vdso_pages = kmalloc(sizeof(struct page *) * npages, GFP_KERNEL);
-	if (!vdso_pages)
-		goto oom;
-	for (i = 0; i < npages; i++) {
-		struct page *p;
-		p = alloc_page(GFP_KERNEL);
-		if (!p)
-			goto oom;
-		vdso_pages[i] = p;
-		copy_page(page_address(p), vdso_start + i*PAGE_SIZE);
-	}
+	for (i = 0; i < npages; i++)
+		vdso_pages[i] = virt_to_page(vdso_start + i*PAGE_SIZE);
 
 	return 0;
-
- oom:
-	printk("Cannot allocate vdso\n");
-	vdso_enabled = 0;
-	return -ENOMEM;
 }
-subsys_initcall(init_vdso_vars);
+subsys_initcall(init_vdso);
 
 struct linux_binprm;
 
-- 
1.7.6

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