Kernel related (?) user space crash at ARM11 MPCore

[Catalin Marinas]

On Thu, 2009-10-15 at 16:28 +0100, Russell King - ARM Linux wrote:
> On Thu, Oct 15, 2009 at 04:20:22PM +0100, Catalin Marinas wrote:
> > On Thu, 2009-10-15 at 15:57 +0100, Russell King - ARM Linux wrote:
> > > On Mon, Sep 21, 2009 at 11:07:51AM +0100, Russell King - ARM Linux wrote:
> > > > On Mon, Sep 21, 2009 at 10:44:23AM +0100, Catalin Marinas wrote:
> > > > > We would need to fix this somehow as well. We currently handle the
> > > > > I-cache in update_mmu_cache() when a page is first mapped if it has
> > > > > VM_EXEC set.
> > > > 
> > > > The reason I'm pushing you hard to separate the two issues is that the
> > > > two should be treated separately.  I think we need to consider ensuring
> > > > that freed pages do not have any I-cache lines associated with them,
> > > > rather than waiting for them to be allocated and then dealing with the
> > > > I-cache problem.
> > > 
> > > Having now benchmarked this (making flush_cache_* always invalidate
> > > the I-cache, so free'd pages are I-cache clean), and to me, the results
> > > quite look promising - please try out this patch.
> > > 
> > > diff --git a/arch/arm/mm/fault-armv.c b/arch/arm/mm/fault-armv.c
> > > index d0d17b6..b9c1cd4 100644
> > > --- a/arch/arm/mm/fault-armv.c
> > > +++ b/arch/arm/mm/fault-armv.c
> > > @@ -160,8 +160,6 @@ void update_mmu_cache(struct vm_area_struct *vma, unsigned long addr, pte_t pte)
> > >  	if (mapping) {
> > >  		if (cache_is_vivt())
> > >  			make_coherent(mapping, vma, addr, pfn);
> > > -		else if (vma->vm_flags & VM_EXEC)
> > > -			__flush_icache_all();
> > >  	}
> > >  }
> > 
> > Before trying the patch, I don't entirely agree with the approach. You
> > will get speculative fetches in the I-cache via the kernel linear
> > mapping (where NX is always cleared) on newer processors and may end up
> > with random faults in user space (not that likely but not impossible
> > either).
> 
> That means we have no option but to flush the I-cache every time a page
> is placed into userspace - we might as well make update_mmu_cache
> unconditionally flush the I-cache every time its called.

We have to look at more than one case: COW text pages, mprotext(RX),
Nitin's scenario with swap pages.

We can flush the D-cache in copy_user_page(), maybe lazily via
flush_dcache_page() and invalidate the I-cache in update_mmu_cache() if
PG_arch_1 (ignoring VM_EXEC).

-- 
Catalin