On Mon, Jul 23, 2018 at 8:42 PM, Fenghua Yu <fenghua...@intel.com> wrote: > On Mon, Jul 23, 2018 at 06:48:00PM -0700, Andy Lutomirski wrote: >> On 07/23/2018 05:55 AM, Fenghua Yu wrote: >> >The instructions can be implemented in intrinsic functions in future >> >GCC. But the vDSO interfaces are available to user without the >> I'm not convinced that any of this belongs in the vDSO at all. You could >> just add AT_HWCAP (or AT_HWCAP2) flags for the new instructions. Or user > > Thomas asked to use vDSO. Please see the discussion thread: > https://lkml.org/lkml/2018/6/19/316
I think he meant that, if these helpers belong in the kernel at all, then they belong in the vDSO. But I think they mostly don't belong in the kernel. > >> code could use CPUID just like for any other new instruction. But, if there >> really is some compelling reason to add this to the vDSO, then see below: >> >+notrace bool __vdso_movdiri_supported(void) >> >+{ >> >+ return _vdso_funcs_data->movdiri_supported; >> return static_cpu_has(X86_FEATURE_MOVDIRI); > > But boot_cpu_data (used in static_cpu_has) cannot be accessed by user > unless mapped in VVAR. So this change cannot be compiled. The underlying alternative infrastructure works in the vDSO. You'd need to introduce an alternate version of _static_cpu_has if BUILD_VDSO that skips the boot_cpu_has fallback.