bug fix patch

bug fix patch

[Kip Macy]

The following patch fixes 3 recent regressions and works around a 4th.

- when debugger trap entry was re-factored the new code neglected to
clear the trace bit in eflags on a trace trap, xc_ptrace now does that
in user-land before continuing

- a merge somewhere along the line removed a validation of the info
pointer in xc_domain_getfullinfo thus causing a seg fault when called
without info (xc_ptrace only wants the cpu context)

- the page not validated case in get_page_type needs to be last, in
the shadow mode code merge it was moved before the general type
checking case - when one tried to do an L2 pin on a page with a
self-reference xen would spin forever in cpu_relax. This patch returns
it to the last case.

 - xen has started to use anonymous unions - this is not c99
compliant. As a workaround freebsd is no longer compiled with -std=c99


http://www.fsmware.com/xen/patches/050417/fixes

RE: bug fix patch

[Ian Pratt]

> - the page not validated case in get_page_type needs to be 
> last, in the shadow mode code merge it was moved before the 
> general type checking case - when one tried to do an L2 pin 
> on a page with a self-reference xen would spin forever in 
> cpu_relax. This patch returns it to the last case.

Your proposal introduces a potantial SMP race, but we're discussing a
better fix.

However, I'm not entirely sure we want to fully support the behaviour
that you are relying on. Why can't you pin the L2 page when its empty
(as we do on Linux), before it contains the linear mapping? 

To fully support this behaviour in the general case, we'd need to handle
arbitrary promotion of pages (e.g. L1->L2 when a linear mapping has been
created to another L2 that has yet to be pinned). We have to do this for
the shadow mode code to support uncooperative OSes, but I'm not sure we
want to support this in the paravirtualized case as it complicates the
code. Special casing self-referential linear mappings (which is what's
causing you the immediate problems) might be OK, but is there any reason
why you can't just do the pinning earlier? 

BTW: if its easy for you, please could you send the other patches
through as separate bk export patches rather than bk send -- our scripts
aren't geared to handle the latter. 

Thanks,
Ian

Re: bug fix patch

[Kip Macy]

> Your proposal introduces a potantial SMP race, but we're discussing a
> better fix.
> 
> However, I'm not entirely sure we want to fully support the behaviour
> that you are relying on. Why can't you pin the L2 page when its empty
> (as we do on Linux), before it contains the linear mapping?

I can and will. It was supported previously so I used it.

> why you can't just do the pinning earlier?
I can.

Per your request I've removed the change to mm.c in:
http://www.fsmware.com/xen/patches/050417/fixes