On Thu, Mar 4, 2021 at 2:16 PM Andy Lutomirski <l...@kernel.org> wrote:
>
> ret_from_fork is written in asm, slightly differently, for x86_32 and
> x86_64. Convert it to C.
>
> This is a straight conversion without any particular cleverness. As a
> further cleanup, the code that sets up the ret_from_fork argument registers
> could be adjusted to put the arguments in the correct registers.
An alternative would be to stash the function pointer and argument in
the pt_regs of the new kthread task, and test for PF_KTHREAD instead.
That would eliminate the need to pass those two values to the C
version of ret_from_fork().
> This will cause the ORC unwinder to find pt_regs even for kernel threads on
> x86_64. This seems harmless.
>
> The 32-bit comment above the now-deleted schedule_tail_wrapper was
> obsolete: the encode_frame_pointer mechanism (see copy_thread()) solves the
> same problem more cleanly.
>
> Cc: Josh Poimboeuf <jpoim...@redhat.com>
> Signed-off-by: Andy Lutomirski <l...@kernel.org>
> ---
> arch/x86/entry/common.c | 23 ++++++++++++++
> arch/x86/entry/entry_32.S | 51 +++++---------------------------
> arch/x86/entry/entry_64.S | 33 +++++----------------
> arch/x86/include/asm/switch_to.h | 2 +-
> arch/x86/kernel/process.c | 2 +-
> arch/x86/kernel/process_32.c | 2 +-
> arch/x86/kernel/unwind_orc.c | 2 +-
> 7 files changed, 43 insertions(+), 72 deletions(-)
>
> diff --git a/arch/x86/entry/common.c b/arch/x86/entry/common.c
> index 95776f16c1cb..ef1c65938a6b 100644
> --- a/arch/x86/entry/common.c
> +++ b/arch/x86/entry/common.c
> @@ -214,6 +214,29 @@ SYSCALL_DEFINE0(ni_syscall)
> return -ENOSYS;
> }
>
> +void ret_from_fork(struct task_struct *prev,
> + int (*kernel_thread_fn)(void *),
> + void *kernel_thread_arg,
> + struct pt_regs *user_regs);
> +
> +__visible void noinstr ret_from_fork(struct task_struct *prev,
> + int (*kernel_thread_fn)(void *),
> + void *kernel_thread_arg,
> + struct pt_regs *user_regs)
> +{
> + instrumentation_begin();
> +
> + schedule_tail(prev);
> +
> + if (kernel_thread_fn) {
This should have an unlikely(), as kernel threads should be the rare case.
--
Brian Gerst
