Re: [PATCHv9 11/16] x86/traps: Communicate a LASS violation in #GP message

[Kirill A. Shutemov]

On Wed, Jul 09, 2025 at 11:36:27AM +0200, Geert Uytterhoeven wrote:
> Hi Kirill,
> 
> On Wed, 9 Jul 2025 at 11:31, Kirill A. Shutemov
> <kirill.shutemov@xxxxxxxxxxxxxxx> wrote:
> > On Tue, Jul 08, 2025 at 07:40:35PM -0700, Sohil Mehta wrote:
> > > > @@ -664,14 +673,23 @@ static enum kernel_gp_hint get_kernel_gp_address(struct pt_regs *regs,
> > > >             return GP_NO_HINT;
> > > >
> > > >  #ifdef CONFIG_X86_64
> > >
> > > Might as well get rid of the #ifdef in C code, if possible.
> > >
> > > if (!IS_ENABLED(CONFIG_X86_64)
> > >       return GP_CANONICAL;
> > >
> > > or combine it with the next check.
> >
> > I tried this before. It triggers compiler error on 32-bit:
> >
> > arch/x86/kernel/traps.c:673:16: error: shift count >= width of type [-Werror,-Wshift-count-overflow]
> >   673 |         if (*addr >= ~__VIRTUAL_MASK)
> >       |                       ^~~~~~~~~~~~~~
> >
> > __VIRTUAL_MASK is not usable on 32-bit configs.
> 
> arch/x86/include/asm/page_32_types.h:#define __VIRTUAL_MASK_SHIFT       32
> arch/x86/include/asm/page_32_types.h:#define __VIRTUAL_MASK_SHIFT       32
> arch/x86/include/asm/page_64_types.h:#define __VIRTUAL_MASK_SHIFT
>  (pgtable_l5_enabled() ? 56 : 47)
> arch/x86/include/asm/page_types.h:#define __VIRTUAL_MASK
>  ((1UL << __VIRTUAL_MASK_SHIFT) - 1)
> 
> Given __VIRTUAL_MASK_SHIFT is 32 on 32-bit platforms, perhaps
> __VIRTUAL_MASK should just be changed to shift 1ULL instead?
> Or better, use GENMASK(__VIRTUAL_MASK_SHIFT - 1, 0), so the
> resulting type is still unsigned long.

Making __VIRTUAL_MASK unsigned long long is no-go. Virtual address are
unsigned long. I guess GENMASK() would work.

I think re-defining __VIRTUAL_MASK is out-of-scope for the patchset. Feel
free to prepare a separate patch to do it.

-- 
  Kiryl Shutsemau / Kirill A. Shutemov