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[Xen-devel] [PATCH 2/3] linux 2.6.18 merge: eliminate Xen specials: alte

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Subject: [Xen-devel] [PATCH 2/3] linux 2.6.18 merge: eliminate Xen specials: alternative.c
From: "Jan Beulich" <jbeulich@xxxxxxxxxx>
Date: Mon, 05 Mar 2007 10:20:50 +0000
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The sole (x86-64 specific) difference of arch/i386/kernel/alternative-xen.c
over its native original can be eliminated by slightly adjusting x86-64's
make_readonly(), and the Xen special can then be removed.

Signed-off-by: Jan Beulich <jbeulich@xxxxxxxxxx>

Index: head-2007-02-27/arch/i386/kernel/alternative-xen.c
===================================================================
--- head-2007-02-27.orig/arch/i386/kernel/alternative-xen.c     2007-02-27 
16:22:53.000000000 +0100
+++ /dev/null   1970-01-01 00:00:00.000000000 +0000
@@ -1,389 +0,0 @@
-#include <linux/module.h>
-#include <linux/spinlock.h>
-#include <linux/list.h>
-#include <asm/alternative.h>
-#include <asm/sections.h>
-
-static int no_replacement    = 0;
-static int smp_alt_once      = 0;
-static int debug_alternative = 0;
-
-static int __init noreplacement_setup(char *s)
-{
-       no_replacement = 1;
-       return 1;
-}
-static int __init bootonly(char *str)
-{
-       smp_alt_once = 1;
-       return 1;
-}
-static int __init debug_alt(char *str)
-{
-       debug_alternative = 1;
-       return 1;
-}
-
-__setup("noreplacement", noreplacement_setup);
-__setup("smp-alt-boot", bootonly);
-__setup("debug-alternative", debug_alt);
-
-#define DPRINTK(fmt, args...) if (debug_alternative) \
-       printk(KERN_DEBUG fmt, args)
-
-#ifdef GENERIC_NOP1
-/* Use inline assembly to define this because the nops are defined
-   as inline assembly strings in the include files and we cannot
-   get them easily into strings. */
-asm("\t.data\nintelnops: "
-       GENERIC_NOP1 GENERIC_NOP2 GENERIC_NOP3 GENERIC_NOP4 GENERIC_NOP5 
GENERIC_NOP6
-       GENERIC_NOP7 GENERIC_NOP8);
-extern unsigned char intelnops[];
-static unsigned char *intel_nops[ASM_NOP_MAX+1] = {
-       NULL,
-       intelnops,
-       intelnops + 1,
-       intelnops + 1 + 2,
-       intelnops + 1 + 2 + 3,
-       intelnops + 1 + 2 + 3 + 4,
-       intelnops + 1 + 2 + 3 + 4 + 5,
-       intelnops + 1 + 2 + 3 + 4 + 5 + 6,
-       intelnops + 1 + 2 + 3 + 4 + 5 + 6 + 7,
-};
-#endif
-
-#ifdef K8_NOP1
-asm("\t.data\nk8nops: "
-       K8_NOP1 K8_NOP2 K8_NOP3 K8_NOP4 K8_NOP5 K8_NOP6
-       K8_NOP7 K8_NOP8);
-extern unsigned char k8nops[];
-static unsigned char *k8_nops[ASM_NOP_MAX+1] = {
-       NULL,
-       k8nops,
-       k8nops + 1,
-       k8nops + 1 + 2,
-       k8nops + 1 + 2 + 3,
-       k8nops + 1 + 2 + 3 + 4,
-       k8nops + 1 + 2 + 3 + 4 + 5,
-       k8nops + 1 + 2 + 3 + 4 + 5 + 6,
-       k8nops + 1 + 2 + 3 + 4 + 5 + 6 + 7,
-};
-#endif
-
-#ifdef K7_NOP1
-asm("\t.data\nk7nops: "
-       K7_NOP1 K7_NOP2 K7_NOP3 K7_NOP4 K7_NOP5 K7_NOP6
-       K7_NOP7 K7_NOP8);
-extern unsigned char k7nops[];
-static unsigned char *k7_nops[ASM_NOP_MAX+1] = {
-       NULL,
-       k7nops,
-       k7nops + 1,
-       k7nops + 1 + 2,
-       k7nops + 1 + 2 + 3,
-       k7nops + 1 + 2 + 3 + 4,
-       k7nops + 1 + 2 + 3 + 4 + 5,
-       k7nops + 1 + 2 + 3 + 4 + 5 + 6,
-       k7nops + 1 + 2 + 3 + 4 + 5 + 6 + 7,
-};
-#endif
-
-#ifdef CONFIG_X86_64
-
-extern char __vsyscall_0;
-static inline unsigned char** find_nop_table(void)
-{
-       return k8_nops;
-}
-
-#else /* CONFIG_X86_64 */
-
-static struct nop {
-       int cpuid;
-       unsigned char **noptable;
-} noptypes[] = {
-       { X86_FEATURE_K8, k8_nops },
-       { X86_FEATURE_K7, k7_nops },
-       { -1, NULL }
-};
-
-static unsigned char** find_nop_table(void)
-{
-       unsigned char **noptable = intel_nops;
-       int i;
-
-       for (i = 0; noptypes[i].cpuid >= 0; i++) {
-               if (boot_cpu_has(noptypes[i].cpuid)) {
-                       noptable = noptypes[i].noptable;
-                       break;
-               }
-       }
-       return noptable;
-}
-
-#endif /* CONFIG_X86_64 */
-
-extern struct alt_instr __alt_instructions[], __alt_instructions_end[];
-extern struct alt_instr __smp_alt_instructions[], __smp_alt_instructions_end[];
-extern u8 *__smp_locks[], *__smp_locks_end[];
-
-extern u8 __smp_alt_begin[], __smp_alt_end[];
-
-/* Replace instructions with better alternatives for this CPU type.
-   This runs before SMP is initialized to avoid SMP problems with
-   self modifying code. This implies that assymetric systems where
-   APs have less capabilities than the boot processor are not handled.
-   Tough. Make sure you disable such features by hand. */
-
-void apply_alternatives(struct alt_instr *start, struct alt_instr *end)
-{
-       unsigned char **noptable = find_nop_table();
-       struct alt_instr *a;
-       u8 *instr;
-       int diff, i, k;
-
-       DPRINTK("%s: alt table %p -> %p\n", __FUNCTION__, start, end);
-       for (a = start; a < end; a++) {
-               BUG_ON(a->replacementlen > a->instrlen);
-               if (!boot_cpu_has(a->cpuid))
-                       continue;
-               instr = a->instr;
-#ifdef CONFIG_X86_64
-               /* vsyscall code is not mapped yet. resolve it manually. */
-               if (instr >= (u8 *)VSYSCALL_START && instr < (u8*)VSYSCALL_END) 
{
-                       instr -= VSYSCALL_START - (unsigned long)&__vsyscall_0;
-                       DPRINTK("%s: vsyscall fixup: %p => %p\n",
-                               __FUNCTION__, a->instr, instr);
-               }
-#endif
-               memcpy(instr, a->replacement, a->replacementlen);
-               diff = a->instrlen - a->replacementlen;
-               /* Pad the rest with nops */
-               for (i = a->replacementlen; diff > 0; diff -= k, i += k) {
-                       k = diff;
-                       if (k > ASM_NOP_MAX)
-                               k = ASM_NOP_MAX;
-                       memcpy(a->instr + i, noptable[k], k);
-               }
-       }
-}
-
-#ifdef CONFIG_SMP
-
-static void alternatives_smp_save(struct alt_instr *start, struct alt_instr 
*end)
-{
-       struct alt_instr *a;
-
-       DPRINTK("%s: alt table %p-%p\n", __FUNCTION__, start, end);
-       for (a = start; a < end; a++) {
-               memcpy(a->replacement + a->replacementlen,
-                      a->instr,
-                      a->instrlen);
-       }
-}
-
-static void alternatives_smp_apply(struct alt_instr *start, struct alt_instr 
*end)
-{
-       struct alt_instr *a;
-
-       for (a = start; a < end; a++) {
-               memcpy(a->instr,
-                      a->replacement + a->replacementlen,
-                      a->instrlen);
-       }
-}
-
-static void alternatives_smp_lock(u8 **start, u8 **end, u8 *text, u8 *text_end)
-{
-       u8 **ptr;
-
-       for (ptr = start; ptr < end; ptr++) {
-               if (*ptr < text)
-                       continue;
-               if (*ptr > text_end)
-                       continue;
-               **ptr = 0xf0; /* lock prefix */
-       };
-}
-
-static void alternatives_smp_unlock(u8 **start, u8 **end, u8 *text, u8 
*text_end)
-{
-       unsigned char **noptable = find_nop_table();
-       u8 **ptr;
-
-       for (ptr = start; ptr < end; ptr++) {
-               if (*ptr < text)
-                       continue;
-               if (*ptr > text_end)
-                       continue;
-               **ptr = noptable[1][0];
-       };
-}
-
-struct smp_alt_module {
-       /* what is this ??? */
-       struct module   *mod;
-       char            *name;
-
-       /* ptrs to lock prefixes */
-       u8              **locks;
-       u8              **locks_end;
-
-       /* .text segment, needed to avoid patching init code ;) */
-       u8              *text;
-       u8              *text_end;
-
-       struct list_head next;
-};
-static LIST_HEAD(smp_alt_modules);
-static DEFINE_SPINLOCK(smp_alt);
-
-void alternatives_smp_module_add(struct module *mod, char *name,
-                                void *locks, void *locks_end,
-                                void *text,  void *text_end)
-{
-       struct smp_alt_module *smp;
-       unsigned long flags;
-
-       if (no_replacement)
-               return;
-
-       if (smp_alt_once) {
-               if (boot_cpu_has(X86_FEATURE_UP))
-                       alternatives_smp_unlock(locks, locks_end,
-                                               text, text_end);
-               return;
-       }
-
-       smp = kzalloc(sizeof(*smp), GFP_KERNEL);
-       if (NULL == smp)
-               return; /* we'll run the (safe but slow) SMP code then ... */
-
-       smp->mod        = mod;
-       smp->name       = name;
-       smp->locks      = locks;
-       smp->locks_end  = locks_end;
-       smp->text       = text;
-       smp->text_end   = text_end;
-       DPRINTK("%s: locks %p -> %p, text %p -> %p, name %s\n",
-               __FUNCTION__, smp->locks, smp->locks_end,
-               smp->text, smp->text_end, smp->name);
-
-       spin_lock_irqsave(&smp_alt, flags);
-       list_add_tail(&smp->next, &smp_alt_modules);
-       if (boot_cpu_has(X86_FEATURE_UP))
-               alternatives_smp_unlock(smp->locks, smp->locks_end,
-                                       smp->text, smp->text_end);
-       spin_unlock_irqrestore(&smp_alt, flags);
-}
-
-void alternatives_smp_module_del(struct module *mod)
-{
-       struct smp_alt_module *item;
-       unsigned long flags;
-
-       if (no_replacement || smp_alt_once)
-               return;
-
-       spin_lock_irqsave(&smp_alt, flags);
-       list_for_each_entry(item, &smp_alt_modules, next) {
-               if (mod != item->mod)
-                       continue;
-               list_del(&item->next);
-               spin_unlock_irqrestore(&smp_alt, flags);
-               DPRINTK("%s: %s\n", __FUNCTION__, item->name);
-               kfree(item);
-               return;
-       }
-       spin_unlock_irqrestore(&smp_alt, flags);
-}
-
-void alternatives_smp_switch(int smp)
-{
-       struct smp_alt_module *mod;
-       unsigned long flags;
-
-#ifdef CONFIG_LOCKDEP
-       /*
-        * A not yet fixed binutils section handling bug prevents
-        * alternatives-replacement from working reliably, so turn
-        * it off:
-        */
-       printk("lockdep: not fixing up alternatives.\n");
-       return;
-#endif
-
-       if (no_replacement || smp_alt_once)
-               return;
-       BUG_ON(!smp && (num_online_cpus() > 1));
-
-       spin_lock_irqsave(&smp_alt, flags);
-       if (smp) {
-               printk(KERN_INFO "SMP alternatives: switching to SMP code\n");
-               clear_bit(X86_FEATURE_UP, boot_cpu_data.x86_capability);
-               clear_bit(X86_FEATURE_UP, cpu_data[0].x86_capability);
-               alternatives_smp_apply(__smp_alt_instructions,
-                                      __smp_alt_instructions_end);
-               list_for_each_entry(mod, &smp_alt_modules, next)
-                       alternatives_smp_lock(mod->locks, mod->locks_end,
-                                             mod->text, mod->text_end);
-       } else {
-               printk(KERN_INFO "SMP alternatives: switching to UP code\n");
-               set_bit(X86_FEATURE_UP, boot_cpu_data.x86_capability);
-               set_bit(X86_FEATURE_UP, cpu_data[0].x86_capability);
-               apply_alternatives(__smp_alt_instructions,
-                                  __smp_alt_instructions_end);
-               list_for_each_entry(mod, &smp_alt_modules, next)
-                       alternatives_smp_unlock(mod->locks, mod->locks_end,
-                                               mod->text, mod->text_end);
-       }
-       spin_unlock_irqrestore(&smp_alt, flags);
-}
-
-#endif
-
-void __init alternative_instructions(void)
-{
-       if (no_replacement) {
-               printk(KERN_INFO "(SMP-)alternatives turned off\n");
-               free_init_pages("SMP alternatives",
-                               (unsigned long)__smp_alt_begin,
-                               (unsigned long)__smp_alt_end);
-               return;
-       }
-       apply_alternatives(__alt_instructions, __alt_instructions_end);
-
-       /* switch to patch-once-at-boottime-only mode and free the
-        * tables in case we know the number of CPUs will never ever
-        * change */
-#ifdef CONFIG_HOTPLUG_CPU
-       if (num_possible_cpus() < 2)
-               smp_alt_once = 1;
-#else
-       smp_alt_once = 1;
-#endif
-
-#ifdef CONFIG_SMP
-       if (smp_alt_once) {
-               if (1 == num_possible_cpus()) {
-                       printk(KERN_INFO "SMP alternatives: switching to UP 
code\n");
-                       set_bit(X86_FEATURE_UP, boot_cpu_data.x86_capability);
-                       set_bit(X86_FEATURE_UP, cpu_data[0].x86_capability);
-                       apply_alternatives(__smp_alt_instructions,
-                                          __smp_alt_instructions_end);
-                       alternatives_smp_unlock(__smp_locks, __smp_locks_end,
-                                               _text, _etext);
-               }
-               free_init_pages("SMP alternatives",
-                               (unsigned long)__smp_alt_begin,
-                               (unsigned long)__smp_alt_end);
-       } else {
-               alternatives_smp_save(__smp_alt_instructions,
-                                     __smp_alt_instructions_end);
-               alternatives_smp_module_add(NULL, "core kernel",
-                                           __smp_locks, __smp_locks_end,
-                                           _text, _etext);
-               alternatives_smp_switch(0);
-       }
-#endif
-}
Index: head-2007-02-27/arch/x86_64/kernel/Makefile
===================================================================
--- head-2007-02-27.orig/arch/x86_64/kernel/Makefile    2007-02-27 
16:27:18.000000000 +0100
+++ head-2007-02-27/arch/x86_64/kernel/Makefile 2007-02-27 16:27:27.000000000 
+0100
@@ -62,7 +62,6 @@ time-y                                += 
../../i386/kernel/time-xen.
 pci-dma-y                      += ../../i386/kernel/pci-dma-xen.o
 microcode-$(subst m,y,$(CONFIG_MICROCODE))  := 
../../i386/kernel/microcode-xen.o
 quirks-y                       := ../../i386/kernel/quirks-xen.o
-alternative-y                  := ../../i386/kernel/alternative-xen.o
 
 n-obj-xen := i8259.o reboot.o i8237.o smpboot.o trampoline.o
 
Index: head-2007-02-27/arch/x86_64/mm/init-xen.c
===================================================================
--- head-2007-02-27.orig/arch/x86_64/mm/init-xen.c      2007-03-05 
10:00:18.000000000 +0100
+++ head-2007-02-27/arch/x86_64/mm/init-xen.c   2007-03-05 10:13:48.000000000 
+0100
@@ -404,6 +404,7 @@ static inline void __set_pte(pte_t *dst,
 
 static inline int make_readonly(unsigned long paddr)
 {
+       extern char __vsyscall_0;
        int readonly = 0;
 
        /* Make new page tables read-only. */
@@ -420,9 +421,12 @@ static inline int make_readonly(unsigned
        /*
         * No need for writable mapping of kernel image. This also ensures that
         * page and descriptor tables embedded inside don't have writable
-        * mappings. 
+        * mappings. Exclude the vsyscall area here, allowing alternative
+        * instruction patching to work.
         */
-       if ((paddr >= __pa_symbol(&_text)) && (paddr < __pa_symbol(&_end)))
+       if ((paddr >= __pa_symbol(&_text)) && (paddr < __pa_symbol(&_end))
+           && !(paddr >= __pa_symbol(&__vsyscall_0)
+                && paddr < __pa_symbol(&__vsyscall_0) + PAGE_SIZE))
                readonly = 1;
 
        return readonly;



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