Re: [PATCH v3 18/26] arm64: Introduce asm/vdso/processor.h

Mark Rutland
2020-03-16T10:29:58Z

On Mon, Mar 16, 2020 at 10:26:22AM +0000, Catalin Marinas wrote:
> On Mon, Mar 16, 2020 at 10:22:15AM +0000, Mark Rutland wrote:
> > On Mon, Mar 16, 2020 at 09:42:32AM +0000, Vincenzo Frascino wrote:
> > > On 3/15/20 6:30 PM, Catalin Marinas wrote:
> > > > On Fri, Mar 13, 2020 at 03:43:37PM +0000, Vincenzo Frascino wrote:
> > > >> +#ifdef CONFIG_COMPAT
> > > >> +#if defined(CONFIG_ARM64_64K_PAGES) && defined(CONFIG_KUSER_HELPERS)
> > > >> +/*
> > > >> + * With CONFIG_ARM64_64K_PAGES enabled, the last page is occupied
> > > >> + * by the compat vectors page.
> > > >> + */
> > > >> +#define TASK_SIZE_32 UL(0x100000000)
> > > >> +#else
> > > >> +#define TASK_SIZE_32 (UL(0x100000000) - PAGE_SIZE)
> > > >> +#endif /* CONFIG_ARM64_64K_PAGES */
> > > >> +#endif /* CONFIG_COMPAT */
> > > >
> > > > Just curious, what's TASK_SIZE_32 used for in the vDSO code? You don't
> > > > seem to move TASK_SIZE.
> > >
> > > I tried to fine grain the headers as much as I could in order to avoid
> > > unneeded/unwanted inclusions:
> > > * TASK_SIZE_32 is used to verify ABI consistency on vdso32 (please refer to
> > > arch/arm64/kernel/vdso32/vgettimeofday.c).
> > > * TASK_SIZE is not required by the vdso library hence it is not present in
> > > these headers.
> >
> > It would be worth noting the former point in the commit message, since
> > it can be surprising.
> >
> > I also think it's worth keeping the definitions together if that's easy,
> > as it makes it easier to navigate the codebase, even if TASK_SIZE isn't
> > necessary for the VDSO itself.
>
> It won't work as TASK_SIZE requires (on arm64) test_thread_flag() which
> can't be made available to the vDSO.

Ah; fair enough.

Thanks,
Mark.