From: Russell King - ARM Linux <linux@xxxxxxxxxxxxxxxx>
Date: Wed, 9 Apr 2014 17:15:55 +0100
> On Wed, Apr 09, 2014 at 12:09:26PM -0400, David Miller wrote:
>> From: Russell King - ARM Linux <linux@xxxxxxxxxxxxxxxx>
>> Date: Wed, 9 Apr 2014 11:01:50 +0100
>>
>> > What has been proposed for uprobes is a uprobe specific function -
>> > flush_uprobe_xol_access() which is used after uprobes writes via the
>> > kmap_atomic() mapping of the page:
>> >
>> > + xol_page_kaddr = kmap_atomic(area->page);
>> > +
>> > + /* Initialize the slot */
>> > + memcpy(xol_page_kaddr + (xol_vaddr & ~PAGE_MASK),
>> > + &uprobe->arch.ixol,
>> > + sizeof(uprobe->arch.ixol));
>> > +
>> > + arch_uprobe_flush_xol_access(area->page, xol_vaddr,
>> > + xol_page_kaddr + (xol_vaddr & ~PAGE_MASK),
>> > + sizeof(uprobe->arch.ixol));
>> > +
>> > + kunmap_atomic(xol_page_kaddr);
>> >
>> > Comments?
>>
>> ptrace() accesses (via __access_remote_vm()) already use an existing
>> helper function for these sorts of situations, in the form of
>> copy_{to,from}_user_page(). I would suggest that uprobes uses that
>> as well.
>
> Yes, I agree with you.
>
> I made that suggestion too (because it's really the same problem)
> but uprobes people are concerned that it's too much of an overhead:
They should use it at first, then if there is a problem we can identify
exactly what can be optimized or needs to be, and expand the interface
as needed.
Let's not optimize first.
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