linux-kernel - Re: [PATCH 2/7] uretprobes: extract fill_page() and trampoline implementation

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Date:	Sun, 24 Mar 2013 15:41:44 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	Anton Arapov <anton@...hat.com>
Cc:	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Josh Stone <jistone@...hat.com>,
	Frank Eigler <fche@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...e.hu>,
	Ananth N Mavinakayanahalli <ananth@...ibm.com>,
	adrian.m.negreanu@...el.com, Torsten.Polle@....de
Subject: Re: [PATCH 2/7] uretprobes: extract fill_page() and trampoline
	implementation

On 03/22, Anton Arapov wrote:
>
> +static void fill_page(struct page *page, unsigned long offset, uprobe_opcode_t *insn)
                                                                  ^^^^^^^^^^^^^^^
Well, it should be "u8 *insn" or "char *".

xol_get_insn_slot() passes arch.insn, and this is not uprobe_opcode_t
in general (see arch/powerpc/include/asm/uprobes.h)

> +{
> +	void *vaddr;
> +
> +	vaddr = kmap_atomic(page);
> +	memcpy(vaddr + offset, insn, MAX_UINSN_BYTES);
                                     ^^^^^^^^^^^^^^^
OK, but see below...

> +	kunmap_atomic(vaddr);
> +
> +	/*
> +	 * We probably need flush_icache_user_range() but it needs vma.
> +	 * This should work on supported architectures too.
> +	 */
> +	flush_dcache_page(page);
> +}

Please do not move flush_dcache_page() from xol_get_insn_slot(),
this is not needed.

Unlike xol_get_insn_slot(), get_xol_area() calls fill_page() before
xol_add_vma().

>  static int xol_add_vma(struct xol_area *area)
>  {
> @@ -1122,6 +1137,7 @@ static struct xol_area *get_xol_area(void)
>  {
>  	struct mm_struct *mm = current->mm;
>  	struct xol_area *area;
> +	uprobe_opcode_t insn = UPROBE_SWBP_INSN;
>
>  	area = mm->uprobes_state.xol_area;
>  	if (area)
> @@ -1139,6 +1155,10 @@ static struct xol_area *get_xol_area(void)
>  	if (!area->page)
>  		goto free_bitmap;
>
> +	/* pre-allocate for return probes */
> +	set_bit(0, area->bitmap);
> +	fill_page(area->page, 0, &insn);

sizeof(insn) == UPROBE_SWBP_INSN_SIZE != MAX_UINSN_BYTES. See also the
comments above.

Oleg.

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