linux-kernel - Re: [patch 2/9] x86/process: Unify copy_thread

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Date:   Fri, 8 Nov 2019 14:31:47 -0800
From:   Andy Lutomirski <luto@...nel.org>
To:     Thomas Gleixner <tglx@...utronix.de>,
        LKML <linux-kernel@...r.kernel.org>
Cc:     x86@...nel.org, Stephen Hemminger <stephen@...workplumber.org>,
        Willy Tarreau <w@....eu>, Juergen Gross <jgross@...e.com>,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        "H. Peter Anvin" <hpa@...or.com>
Subject: Re: [patch 2/9] x86/process: Unify copy_thread_tls()

On 11/6/19 11:35 AM, Thomas Gleixner wrote:
> While looking at the TSS io bitmap it turned out that any change in that
> area would require identical changes to copy_thread_tls(). The 32 and 64
> bit variants share sufficient code to consolidate them into a common
> function to avoid duplication of upcoming modifications.
> 
> Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
> ---
>  arch/x86/include/asm/ptrace.h    |    6 ++
>  arch/x86/include/asm/switch_to.h |   10 ++++
>  arch/x86/kernel/process.c        |   94 +++++++++++++++++++++++++++++++++++++++
>  arch/x86/kernel/process_32.c     |   68 ----------------------------
>  arch/x86/kernel/process_64.c     |   75 -------------------------------
>  5 files changed, 110 insertions(+), 143 deletions(-)
> 
> --- a/arch/x86/include/asm/ptrace.h
> +++ b/arch/x86/include/asm/ptrace.h
> @@ -361,5 +361,11 @@ extern int do_get_thread_area(struct tas
>  extern int do_set_thread_area(struct task_struct *p, int idx,
>  			      struct user_desc __user *info, int can_allocate);
>  
> +#ifdef CONFIG_X86_64
> +# define do_set_thread_area_64(p, s, t)	do_arch_prctl_64(p, s, t)
> +#else
> +# define do_set_thread_area_64(p, s, t)	(0)
> +#endif
> +
>  #endif /* !__ASSEMBLY__ */
>  #endif /* _ASM_X86_PTRACE_H */
> --- a/arch/x86/include/asm/switch_to.h
> +++ b/arch/x86/include/asm/switch_to.h
> @@ -103,7 +103,17 @@ static inline void update_task_stack(str
>  	if (static_cpu_has(X86_FEATURE_XENPV))
>  		load_sp0(task_top_of_stack(task));
>  #endif
> +}
>  
> +static inline void kthread_frame_init(struct inactive_task_frame *frame,
> +				      unsigned long fun, unsigned long arg)
> +{
> +	frame->bx = fun;
> +#ifdef CONFIG_X86_32
> +	frame->di = arg;
> +#else
> +	frame->r12 = arg;
> +#endif
>  }
>  
>  #endif /* _ASM_X86_SWITCH_TO_H */
> --- a/arch/x86/kernel/process.c
> +++ b/arch/x86/kernel/process.c
> @@ -132,6 +132,100 @@ void exit_thread(struct task_struct *tsk
>  	fpu__drop(fpu);
>  }
>  
> +static int set_new_tls(struct task_struct *p, unsigned long tls)
> +{
> +	struct user_desc __user *utls = (struct user_desc __user *)tls;
> +
> +	if (in_ia32_syscall())
> +		return do_set_thread_area(p, -1, utls, 0);
> +	else
> +		return do_set_thread_area_64(p, ARCH_SET_FS, tls);
> +}
> +
> +static inline int copy_io_bitmap(struct task_struct *tsk)
> +{
> +	if (likely(!test_tsk_thread_flag(current, TIF_IO_BITMAP)))
> +		return 0;
> +
> +	tsk->thread.io_bitmap_ptr = kmemdup(current->thread.io_bitmap_ptr,
> +					    IO_BITMAP_BYTES, GFP_KERNEL);

tsk->thread.io_bitmap_max = current->thread.io_bitmap_max?

I realize you inherited this from the code you're refactoring, but it
does seem to be missing.

> +	if (!tsk->thread.io_bitmap_ptr) {
> +		tsk->thread.io_bitmap_max = 0;
> +		return -ENOMEM;
> +	}
> +	set_tsk_thread_flag(tsk, TIF_IO_BITMAP);
> +	return 0;
> +}
> +
> +static inline void free_io_bitmap(struct task_struct *tsk)
> +{
> +	if (tsk->thread.io_bitmap_ptr) {
> +		kfree(tsk->thread.io_bitmap_ptr);
> +		tsk->thread.io_bitmap_ptr = NULL;
> +		tsk->thread.io_bitmap_max = 0;
> +	}
> +}
> +
> +int copy_thread_tls(unsigned long clone_flags, unsigned long sp,
> +		    unsigned long arg, struct task_struct *p, unsigned long tls)
> +{
> +	struct inactive_task_frame *frame;
> +	struct fork_frame *fork_frame;
> +	struct pt_regs *childregs;
> +	int ret;
> +
> +	childregs = task_pt_regs(p);
> +	fork_frame = container_of(childregs, struct fork_frame, regs);
> +	frame = &fork_frame->frame;
> +
> +	frame->bp = 0;
> +	frame->ret_addr = (unsigned long) ret_from_fork;
> +	p->thread.sp = (unsigned long) fork_frame;
> +	p->thread.io_bitmap_ptr = NULL;
> +	memset(p->thread.ptrace_bps, 0, sizeof(p->thread.ptrace_bps));
> +
> +#ifdef CONFIG_X86_64
> +	savesegment(gs, p->thread.gsindex);
> +	p->thread.gsbase = p->thread.gsindex ? 0 : current->thread.gsbase;
> +	savesegment(fs, p->thread.fsindex);
> +	p->thread.fsbase = p->thread.fsindex ? 0 : current->thread.fsbase;
> +	savesegment(es, p->thread.es);
> +	savesegment(ds, p->thread.ds);
> +#else
> +	/* Clear all status flags including IF and set fixed bit. */
> +	frame->flags = X86_EFLAGS_FIXED;
> +#endif

Want to do another commit to make the eflags fixup unconditional?  I'm
wondering if we have a bug.

Other than these questions:

Acked-by: Andy Lutomirski <luto@...nel.org>