Re: [PATCH] kvm: x86: mmu: Add cast to negated bitmasks in update_permission_bitmask()

[Joe Perches]

On Tue, 2018-06-19 at 19:35 +0200, Paolo Bonzini wrote:
> On 19/06/2018 19:23, Joe Perches wrote:
> > On Tue, 2018-06-19 at 10:08 -0700, Nick Desaulniers wrote:
> > > On Tue, Jun 19, 2018 at 8:19 AM Paolo Bonzini <pbonzini@xxxxxxxxxx> wrote:
> > > > 
> > > > On 15/06/2018 20:45, Nick Desaulniers wrote:
> > > > > > 
> > > > > > > In any case I think it it preferable to fix the code over disabling
> > > > > > > the warning, unless the warning is bogus or there are just too many
> > > > > > > occurrences.
> > > > > > 
> > > > > > Maybe.
> > > > > 
> > > > > Spurious warning today, actual bug tomorrow?  I prefer to not to
> > > > > disable warnings wholesale.  They don't need to find actual bugs to be
> > > > > useful.  Flagging code that can be further specified does not hurt.
> > > > > Part of the effort to compile the kernel with different compilers is
> > > > > to add warning coverage, not remove it.  That said, there may be
> > > > > warnings that are never useful (or at least due to some invariant that
> > > > > only affects the kernel).  I cant think of any off the top of my head,
> > > > > but I'm also not sure this is one.
> > > > 
> > > > This one really makes the code uglier though, so I'm not really inclined
> > > > to applying the patch.
> > > 
> > > Note that of the three variables (w, u, x), only u is used later on.
> > > What about declaring them as negated with the cast, that way there's
> > > no cast in a ternary?
> > 
> > It'd be simpler to cast in the BYTE_MASK macro itself
> 
> I don't think that would work, as the ~ would be done on a zero-extended
> signed int.

True, but the whole concept is dubious.
The implicit casts are all over the place,
not just in the file.