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; -- To unsubscribe from this list: send the line "unsubscribe linux-nfs" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
