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s390/ftrace: Avoid trampolines if possible

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When a sequential instruction fetching facility is present, it is safe
to patch ftrace NOPs in function prologues. All of them are 8-byte
aligned.

Reviewed-by: Heiko Carstens <hca@linux.ibm.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>
This commit is contained in:
Vasily Gorbik
2024-08-28 19:06:55 +02:00
parent 30799152c3
commit efd9cd019e
1 changed files with 53 additions and 6 deletions
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59
arch/s390/kernel/ftrace.c
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@@ -69,7 +69,7 @@ static const char *ftrace_shared_hotpatch_trampoline(const char **end)
bool ftrace_need_init_nop(void)
{
return true;
return !MACHINE_HAS_SEQ_INSN;
}
int ftrace_init_nop(struct module *mod, struct dyn_ftrace *rec)
@@ -139,8 +139,35 @@ static struct ftrace_hotpatch_trampoline *ftrace_get_trampoline(struct dyn_ftrac
return trampoline;
}
int ftrace_modify_call(struct dyn_ftrace *rec, unsigned long old_addr,
unsigned long addr)
static inline struct ftrace_insn
ftrace_generate_branch_insn(unsigned long ip, unsigned long target)
{
/* brasl r0,target or brcl 0,0 */
return (struct ftrace_insn){ .opc = target ? 0xc005 : 0xc004,
.disp = target ? (target - ip) / 2 : 0 };
}
static int ftrace_patch_branch_insn(unsigned long ip, unsigned long old_target,
unsigned long target)
{
struct ftrace_insn orig = ftrace_generate_branch_insn(ip, old_target);
struct ftrace_insn new = ftrace_generate_branch_insn(ip, target);
struct ftrace_insn old;
if (!IS_ALIGNED(ip, 8))
return -EINVAL;
if (copy_from_kernel_nofault(&old, (void *)ip, sizeof(old)))
return -EFAULT;
/* Verify that the to be replaced code matches what we expect. */
if (memcmp(&orig, &old, sizeof(old)))
return -EINVAL;
s390_kernel_write((void *)ip, &new, sizeof(new));
return 0;
}
static int ftrace_modify_trampoline_call(struct dyn_ftrace *rec,
unsigned long old_addr,
unsigned long addr)
{
struct ftrace_hotpatch_trampoline *trampoline;
u64 old;
@@ -156,6 +183,15 @@ int ftrace_modify_call(struct dyn_ftrace *rec, unsigned long old_addr,
return 0;
}
int ftrace_modify_call(struct dyn_ftrace *rec, unsigned long old_addr,
unsigned long addr)
{
if (MACHINE_HAS_SEQ_INSN)
return ftrace_patch_branch_insn(rec->ip, old_addr, addr);
else
return ftrace_modify_trampoline_call(rec, old_addr, addr);
}
static int ftrace_patch_branch_mask(void *addr, u16 expected, bool enable)
{
u16 old;
@@ -174,11 +210,14 @@ static int ftrace_patch_branch_mask(void *addr, u16 expected, bool enable)
int ftrace_make_nop(struct module *mod, struct dyn_ftrace *rec,
unsigned long addr)
{
/* Expect brcl 0xf,... */
return ftrace_patch_branch_mask((void *)rec->ip, 0xc0f4, false);
/* Expect brcl 0xf,... for the !MACHINE_HAS_SEQ_INSN case */
if (MACHINE_HAS_SEQ_INSN)
return ftrace_patch_branch_insn(rec->ip, addr, 0);
else
return ftrace_patch_branch_mask((void *)rec->ip, 0xc0f4, false);
}
int ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr)
static int ftrace_make_trampoline_call(struct dyn_ftrace *rec, unsigned long addr)
{
struct ftrace_hotpatch_trampoline *trampoline;
@@ -190,6 +229,14 @@ int ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr)
return ftrace_patch_branch_mask((void *)rec->ip, 0xc004, true);
}
int ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr)
{
if (MACHINE_HAS_SEQ_INSN)
return ftrace_patch_branch_insn(rec->ip, 0, addr);
else
return ftrace_make_trampoline_call(rec, addr);
}
int ftrace_update_ftrace_func(ftrace_func_t func)
{
ftrace_func = func;