Christophe Leroy wrote:
+ S390 people
Le 15/02/2022 à 15:28, Christophe Leroy a écrit :
Le 15/02/2022 à 14:36, Naveen N. Rao a écrit :
Michael Ellerman wrote:
Christophe Leroy <christophe.leroy@xxxxxxxxxx> writes:
Le 14/02/2022 à 16:25, Naveen N. Rao a écrit :
Christophe Leroy wrote:
Implement CONFIG_DYNAMIC_FTRACE_WITH_ARGS. It accelerates the call
of livepatching.
Also note that powerpc being the last one to convert to
CONFIG_DYNAMIC_FTRACE_WITH_ARGS, it will now be possible to remove
klp_arch_set_pc() on all architectures.
Signed-off-by: Christophe Leroy <christophe.leroy@xxxxxxxxxx>
---
arch/powerpc/Kconfig | 1 +
arch/powerpc/include/asm/ftrace.h | 17 +++++++++++++++++
arch/powerpc/include/asm/livepatch.h | 4 +---
3 files changed, 19 insertions(+), 3 deletions(-)
diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
index cdac2115eb00..e2b1792b2aae 100644
--- a/arch/powerpc/Kconfig
+++ b/arch/powerpc/Kconfig
@@ -210,6 +210,7 @@ config PPC
select HAVE_DEBUG_KMEMLEAK
select HAVE_DEBUG_STACKOVERFLOW
select HAVE_DYNAMIC_FTRACE
+ select HAVE_DYNAMIC_FTRACE_WITH_ARGS if MPROFILE_KERNEL ||
PPC32
select HAVE_DYNAMIC_FTRACE_WITH_REGS if MPROFILE_KERNEL ||
PPC32
select HAVE_EBPF_JIT
select HAVE_EFFICIENT_UNALIGNED_ACCESS if
!(CPU_LITTLE_ENDIAN && POWER7_CPU)
diff --git a/arch/powerpc/include/asm/ftrace.h
b/arch/powerpc/include/asm/ftrace.h
index b3f6184f77ea..45c3d6f11daa 100644
--- a/arch/powerpc/include/asm/ftrace.h
+++ b/arch/powerpc/include/asm/ftrace.h
@@ -22,6 +22,23 @@ static inline unsigned long
ftrace_call_adjust(unsigned long addr)
struct dyn_arch_ftrace {
struct module *mod;
};
+
+#ifdef CONFIG_DYNAMIC_FTRACE_WITH_ARGS
+struct ftrace_regs {
+ struct pt_regs regs;
+};
+
+static __always_inline struct pt_regs
*arch_ftrace_get_regs(struct ftrace_regs *fregs)
+{
+ return &fregs->regs;
+}
I think this is wrong. We need to differentiate between
ftrace_caller() and ftrace_regs_caller() here, and only return
pt_regs if coming in through ftrace_regs_caller() (i.e.,
FL_SAVE_REGS is set).
Not sure I follow you.
This is based on 5740a7c71ab6 ("s390/ftrace: add
HAVE_DYNAMIC_FTRACE_WITH_ARGS support")
It's all the point of HAVE_DYNAMIC_FTRACE_WITH_ARGS, have the regs
also with ftrace_caller().
Sure you only have the params, but that's the same on s390, so what
did I miss ?
Steven has explained the rationale for this in his other response:
https://lore.kernel.org/all/20220215093849.556d5444@xxxxxxxxxxxxxxxxxx/
It looks like s390 is special since it apparently saves all registers
even for ftrace_caller:
https://lore.kernel.org/all/YbipdU5X4HNDWIni@osiris/
It is not what I understand from their code, see
https://elixir.bootlin.com/linux/v5.17-rc3/source/arch/s390/kernel/mcount.S#L37
They have a common macro called with argument 'allregs' which is set to
0 for ftrace_caller() and 1 for ftrace_regs_caller().
When allregs == 1, the macro seems to save more.
But ok, I can do like x86, but I need a trick to know whether
FL_SAVE_REGS is set or not, like they do with fregs->regs.cs
Any idea what the condition can be for powerpc ?
We'll need to explicitly zero-out something in pt_regs in
ftrace_caller(). We can probably use regs->msr since we don't expect it
to be zero when saved from ftrace_regs_caller().
Finally, it looks like this change is done via commit 894979689d3a
("s390/ftrace: provide separate ftrace_caller/ftrace_regs_caller
implementations") four hours the same day after the implementation of
arch_ftrace_get_regs()
They may have forgotten to change arch_ftrace_get_regs() which was added
in commit 5740a7c71ab6 ("s390/ftrace: add HAVE_DYNAMIC_FTRACE_WITH_ARGS
support") with the assumption that ftrace_caller and ftrace_regs_caller
where identical.
Indeed, good find!
Thanks,
Naveen
