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Date: Wed, 28 Jul 2010 07:00:43 -0400
From: Xiaotian Feng <dfeng@...hat.com>
To: linux-mm@...ck.org, linux-nfs@...r.kernel.org,
netdev@...r.kernel.org
Cc: cl@...ux-foundation.org, a.p.zijlstra@...llo.nl,
Xiaotian Feng <dfeng@...hat.com>, lwang@...hat.com,
penberg@...helsinki.fi, davem@...emloft.net
Subject: [PATCH RHEL6 RESEND] kernel performance optimization with CONFIG_DEBUG_RODATA
backport of following commits to improve x86_64 kernel performance with
CONFIG_DEBUG_RODATA:
straightforward backport of:
commit b9af7c0d (x86-64: preserve large page mapping for 1st 2MB kernel txt with CONFIG_DEBUG_RODATA)
commit 74e08179 (x86-64: align RODATA kernel section to 2MB with CONFIG_DEBUG_RODATA)
commit d6cc1c3a (x86-64: add comment for RODATA large page retainment)
Resolves bz557364
We still have CONFIG_DEBUG_RODATA set for regular rhel6 kernel, so this fix is still needed.
There's no kabi breakage with latest rhel6 code (don't know why...)
Brew build is available at:
https://brewweb.devel.redhat.com/taskinfo?taskID=2627856
Test has been done for RHTS kernel tier1:
http://rhts.redhat.com/cgi-bin/rhts/jobs.cgi?id=168225
No regressions are introduced by this patch. Reviews and comments are welcome.
---
--- a/arch/x86/include/asm/sections.h
+++ b/arch/x86/include/asm/sections.h
@@ -2,7 +2,13 @@
#define _ASM_X86_SECTIONS_H
#include <asm-generic/sections.h>
+#include <asm/uaccess.h>
extern char __brk_base[], __brk_limit[];
+extern struct exception_table_entry __stop___ex_table[];
+
+#if defined(CONFIG_X86_64) && defined(CONFIG_DEBUG_RODATA)
+extern char __end_rodata_hpage_align[];
+#endif
#endif /* _ASM_X86_SECTIONS_H */
--- a/arch/x86/kernel/head_64.S
+++ b/arch/x86/kernel/head_64.S
@@ -262,11 +262,11 @@ ENTRY(secondary_startup_64)
.quad x86_64_start_kernel
ENTRY(initial_gs)
.quad INIT_PER_CPU_VAR(irq_stack_union)
- __FINITDATA
ENTRY(stack_start)
.quad init_thread_union+THREAD_SIZE-8
.word 0
+ __FINITDATA
bad_address:
jmp bad_address
@@ -340,6 +340,7 @@ ENTRY(name)
i = i + 1 ; \
.endr
+ .data
/*
* This default setting generates an ident mapping at address 0x100000
* and a mapping for the kernel that precisely maps virtual address
--- a/arch/x86/kernel/vmlinux.lds.S
+++ b/arch/x86/kernel/vmlinux.lds.S
@@ -41,6 +41,32 @@ ENTRY(phys_startup_64)
jiffies_64 = jiffies;
#endif
+#if defined(CONFIG_X86_64) && defined(CONFIG_DEBUG_RODATA)
+/*
+ * On 64-bit, align RODATA to 2MB so that even with CONFIG_DEBUG_RODATA
+ * we retain large page mappings for boundaries spanning kernel text, rodata
+ * and data sections.
+ *
+ * However, kernel identity mappings will have different RWX permissions
+ * to the pages mapping to text and to the pages padding (which are freed) the
+ * text section. Hence kernel identity mappings will be broken to smaller
+ * pages. For 64-bit, kernel text and kernel identity mappings are different,
+ * so we can enable protection checks that come with CONFIG_DEBUG_RODATA,
+ * as well as retain 2MB large page mappings for kernel text.
+ */
+#define X64_ALIGN_DEBUG_RODATA_BEGIN . = ALIGN(HPAGE_SIZE);
+
+#define X64_ALIGN_DEBUG_RODATA_END \
+ . = ALIGN(HPAGE_SIZE); \
+ __end_rodata_hpage_align = .;
+
+#else
+
+#define X64_ALIGN_DEBUG_RODATA_BEGIN
+#define X64_ALIGN_DEBUG_RODATA_END
+
+#endif
+
PHDRS {
text PT_LOAD FLAGS(5); /* R_E */
data PT_LOAD FLAGS(7); /* RWE */
@@ -90,7 +116,9 @@ SECTIONS
EXCEPTION_TABLE(16) :text = 0x9090
+ X64_ALIGN_DEBUG_RODATA_BEGIN
RO_DATA(PAGE_SIZE)
+ X64_ALIGN_DEBUG_RODATA_END
/* Data */
.data : AT(ADDR(.data) - LOAD_OFFSET) {
--- a/arch/x86/mm/init_64.c
+++ b/arch/x86/mm/init_64.c
@@ -761,7 +761,7 @@ static int kernel_set_to_readonly;
void set_kernel_text_rw(void)
{
- unsigned long start = PFN_ALIGN(_stext);
+ unsigned long start = PFN_ALIGN(_text);
unsigned long end = PFN_ALIGN(__start_rodata);
if (!kernel_set_to_readonly)
@@ -775,7 +775,7 @@ void set_kernel_text_rw(void)
void set_kernel_text_ro(void)
{
- unsigned long start = PFN_ALIGN(_stext);
+ unsigned long start = PFN_ALIGN(_text);
unsigned long end = PFN_ALIGN(__start_rodata);
if (!kernel_set_to_readonly)
@@ -789,9 +789,13 @@ void set_kernel_text_ro(void)
void mark_rodata_ro(void)
{
- unsigned long start = PFN_ALIGN(_stext), end = PFN_ALIGN(__end_rodata);
+ unsigned long start = PFN_ALIGN(_text);
unsigned long rodata_start =
((unsigned long)__start_rodata + PAGE_SIZE - 1) & PAGE_MASK;
+ unsigned long end = (unsigned long) &__end_rodata_hpage_align;
+ unsigned long text_end = PAGE_ALIGN((unsigned long) &__stop___ex_table);
+ unsigned long rodata_end = PAGE_ALIGN((unsigned long) &__end_rodata);
+ unsigned long data_start = (unsigned long) &_sdata;
printk(KERN_INFO "Write protecting the kernel read-only data: %luk\n",
(end - start) >> 10);
@@ -814,6 +818,14 @@ void mark_rodata_ro(void)
printk(KERN_INFO "Testing CPA: again\n");
set_memory_ro(start, (end-start) >> PAGE_SHIFT);
#endif
+
+ free_init_pages("unused kernel memory",
+ (unsigned long) page_address(virt_to_page(text_end)),
+ (unsigned long)
+ page_address(virt_to_page(rodata_start)));
+ free_init_pages("unused kernel memory",
+ (unsigned long) page_address(virt_to_page(rodata_end)),
+ (unsigned long) page_address(virt_to_page(data_start)));
}
#endif
--- a/arch/x86/mm/pageattr.c
+++ b/arch/x86/mm/pageattr.c
@@ -279,6 +279,20 @@ static inline pgprot_t static_protections(pgprot_t prot, unsigned long address,
__pa((unsigned long)__end_rodata) >> PAGE_SHIFT))
pgprot_val(forbidden) |= _PAGE_RW;
+#if defined(CONFIG_X86_64) && defined(CONFIG_DEBUG_RODATA)
+ /*
+ * Kernel text mappings for the large page aligned .rodata section
+ * will be read-only. For the kernel identity mappings covering
+ * the holes caused by this alignment can be anything.
+ *
+ * This will preserve the large page mappings for kernel text/data
+ * at no extra cost.
+ */
+ if (within(address, (unsigned long)_text,
+ (unsigned long)__end_rodata_hpage_align))
+ pgprot_val(forbidden) |= _PAGE_RW;
+#endif
+
prot = __pgprot(pgprot_val(prot) & ~pgprot_val(forbidden));
return prot;
--
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