Re: [PATCH?] uprobes: change uprobe_write_opcode() to modify the page directly

H. Peter Anvin
2013-12-03T23:49:05Z

On 12/03/2013 02:01 PM, Linus Torvalds wrote:
> On Tue, Dec 3, 2013 at 12:54 PM, Oleg Nesterov <oleg@redhat.com> wrote:
>>
>> So do you think the patch I sent is wrong? Why?
>
> I think the TLB shootdown should guarantee that it's ok on other
> CPU's, since that's basically what we do on mmap.
>

I think that is true for other CPUs; however, there are definitely CPUs
out there (which Linux supports) for which you have to synchronize the I
and D sides "manually" after writing code through memory, at least
through the CPU. That is at least one reason why MIPS has a
cacheflush() system call, for example.

> But looking closer at this, I think I see why the old code did what it
> did. I think it's breaking shared mmap pages on purpose rather than
> dirtying them. Which is probably the right thing to do.
>

In other words, treating them as MAP_PRIVATE? Wouldn't it be better to
throw an error if we can't honor the semantics of the mapping that we
are using?

-hpa