Re: [uml-devel] a question about sigsetjmp() in copy_from/to_user()

[Blaisorblade <blaisorblade@yahoo.it>]

On Wednesday 28 September 2005 18:09, Jeff Dike wrote:
> On Wed, Sep 28, 2005 at 01:59:48PM +0200, Blaisorblade wrote:

> > That wasn't the original reason - this is fine too, but as I explained in
> > the other mail, cat /dev/kmem will cause a copy_to_user() with invalid
> > kernel ("from") address. I remember because I discussed this with you at
> > length.

> Oh yeah.  I was thinking there was a different (and better) reason, but I
> couldn't remember what it was.

> Also, my reason isn't that good anyway.  I had a different fix a while ago,
> but it got lost somewhere.  I added an arch hook to get_free_pages which
> touched each allocated page under the cover of a setjmp.  If a page
> couldn't be allocated on the host, then it is put on a "bad pages" list,
> and another page is allocated instead.
I'm not sure that would help anyway - if the host memory is full, it's full. 
It's just matter of waiting and retrying.

I don't think the host would SIGBUS again on the same page specifically - or 
better, I'm almost sure this is not done.
So, I don't see the reason for that. Catching SIGSEGV/SIGBUS is ok, taking 
another page is bad.
-- 
Inform me of my mistakes, so I can keep imitating Homer Simpson's "Doh!".
Paolo Giarrusso, aka Blaisorblade (Skype ID "PaoloGiarrusso", ICQ 215621894)
http://www.user-mode-linux.org/~blaisorblade

	

	
		
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