Re: [PATCH] Add memory clobber to hypercalls (v2)

[Hollis Blanchard <hollisb@us.ibm.com>]

On Sat, 2008-06-28 at 06:43 +0300, Avi Kivity wrote:
> Anthony Liguori wrote:
> > Hypercalls can modify arbitrary regions of memory.  Make sure to indicate this
> > in the clobber list.  This fixes a hang when using KVM_GUEST kernel built with
> > GCC 4.3.0.
> >
> > This was originally spotted and analyzed by Marcelo.
> >
> > Since v1, I've also added a "m" constraint for the inputs to the hypercall.
> > This was suggested by Christian since it's not entirely clear whether a memory
> > clobber will force the data to be in memory before the asm statement.  In the
> > very least, it helps to be more conservative.
> >
> > Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>
> >
> > @@ -80,7 +81,9 @@ static inline long kvm_hypercall1(unsigned int nr, unsigned long p1)
> >  	long ret;
> >  	asm volatile(KVM_HYPERCALL
> >  		     : "=a"(ret)
> > -		     : "a"(nr), "b"(p1));
> > +		     : "a"(nr), "b"(p1),
> > +		       "m"(*(char *)p1)
> > +		     : "memory");
> >  	return ret;
> >  }
> >  
> >   
> 
> Those are physical addresses, not virtual, and on i386 the addresses are 
> split across multiple registers.
> 
> However a small test program shows that the memory clobber does work 
> with gcc 4.3, so I'll pick the earlier patch.

What about gcc 4.4? 4.5? 5.0?

-- 
Hollis Blanchard
IBM Linux Technology Center