On Thu, Feb 09, 2023 at 03:21:55PM +0100, Ard Biesheuvel wrote: > On Wed, 8 Feb 2023 at 15:36, Ard Biesheuvel <ardb@xxxxxxxxxx> wrote: > > On Wed, 8 Feb 2023 at 15:25, Mark Rutland <mark.rutland@xxxxxxx> wrote: > > > I believe that there's no issue with mismatched CPUs, but there *might* might > > > be a different issue with the ordering of feature detection and usage of the > > > cap: > > > > > > * If CONFIG_ARM64_BTI_KERNEL=y, then the ARM64_BTI cap is detected as a strict > > > boot cpu feature, and secondaries without it will be rejected. > > > > > > * If CONFIG_ARM64_BTI_KERNEL=n then the ARM64_BTI cap is detected as a system > > > feature, and so we only set the cap bit after bringing all secondary CPUs > > > online, and only when *all* CPUs support it. > > > > > > The happens under setup_cpu_features(), called from smp_cpus_done(). > > > > > > So there's no issue with mismatch, but if system_supports_bti is called before > > > smp_cpus_done() on a CONFIG_ARM64_BTI_KERNEL kernel it will return false. When > > > do we set up the EFI mappings relative to that? > > > > > > > Currently it is an early initcall so before SMP, but that is not > > really necessary - the EFI table that carries this annotation is an > > overlay that could easily be applied later. > > > > OTOH, what is the penalty for setting the GP attribute and using the > > translation table on a core that does not implement BTI? > > I'll merge this with the CONFIG_ARM64_BTI_KERNEL check re-added, if > nobody minds? That make sense to me; with the CONFIG_ARM64_BTI_KERNEL check: Acked-by: Mark Rutland <mark.rutland@xxxxxxx> Mark.
