Re: [PATCH 2/2] arm/xen: Add misuse warning to virt_to_gfn

[Stefano Stabellini <sstabellini@xxxxxxxxxx>]

On Tue, 25 Aug 2020, Jan Beulich wrote:
> On 25.08.2020 11:31, Simon Leiner wrote:
> > --- a/include/xen/arm/page.h
> > +++ b/include/xen/arm/page.h
> > @@ -76,7 +76,11 @@ static inline unsigned long bfn_to_pfn(unsigned long bfn)
> >  #define bfn_to_local_pfn(bfn)      bfn_to_pfn(bfn)
> >  
> >  /* VIRT <-> GUEST conversion */
> > -#define virt_to_gfn(v)             (pfn_to_gfn(virt_to_phys(v) >> 
> > XEN_PAGE_SHIFT))
> > +#define virt_to_gfn(v)                                                     
> >     \
> > +   ({                                                                     \
> > +           WARN_ON_ONCE(is_vmalloc_addr(v));                              \
> > +           pfn_to_gfn(virt_to_phys(v) >> XEN_PAGE_SHIFT);                 \
> > +   })
> 
> Shouldn't such a check cover more than just the vmalloc range,
> i.e. everything outside of what __va() can validly return?

Keep in mind that this patch is meant as sister patch to
https://marc.info/?l=xen-devel&m=159834800203817
so it makes sense to check for vmalloc addresses specifically.

That said, I am not aware of a good way to implement the __va test you
are suggesting.