Re: [PATCH 4/5] powerpc: Define config option for processors without broadcast TLBIE

["Nicholas Piggin" <npiggin@gmail.com>]

On Wed Jan 29, 2025 at 8:53 AM AEST, Paul Mackerras wrote:
> Power ISA v3.1 implementations in the Linux Compliancy Subset and
> lower are not required to implement broadcast TLBIE, and in fact
> Microwatt doesn't.  To avoid the need to specify "disable_tlbie" on
> the kernel command line on SMP Microwatt systems, this defines a
> config option that asserts that broadcast TLBIE should never be used
> (the kernel will instead use IPIs to trigger local TLBIEs on other
> CPUs when required).
>
> Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
> ---
>  arch/powerpc/mm/book3s64/pgtable.c       | 10 ++++++++--
>  arch/powerpc/platforms/Kconfig.cputype   | 12 ++++++++++++
>  arch/powerpc/platforms/microwatt/Kconfig |  1 +
>  3 files changed, 21 insertions(+), 2 deletions(-)
>
> diff --git a/arch/powerpc/mm/book3s64/pgtable.c b/arch/powerpc/mm/book3s64/pgtable.c
> index 374542528080..14ee96e2a581 100644
> --- a/arch/powerpc/mm/book3s64/pgtable.c
> +++ b/arch/powerpc/mm/book3s64/pgtable.c
> @@ -588,10 +588,16 @@ int pmd_move_must_withdraw(struct spinlock *new_pmd_ptl,
>  }
>  #endif
>  
> +#ifndef CONFIG_PPC_RADIX_NO_BROADCAST_TLBIE

Hate to bikeshed, but would it be annoying to make this an affirmative
option?

> +#define DEFAULT_TLBIE_ENABLE	true
> +#else
> +#define DEFAULT_TLBIE_ENABLE	false
> +#endif
> +
>  /*
>   * Does the CPU support tlbie?
>   */
> -bool tlbie_capable __read_mostly = true;
> +bool tlbie_capable __read_mostly = DEFAULT_TLBIE_ENABLE;
>  EXPORT_SYMBOL(tlbie_capable);
>  
>  /*
> @@ -599,7 +605,7 @@ EXPORT_SYMBOL(tlbie_capable);
>   * address spaces? tlbie may still be used for nMMU accelerators, and for KVM
>   * guest address spaces.
>   */
> -bool tlbie_enabled __read_mostly = true;
> +bool tlbie_enabled __read_mostly = DEFAULT_TLBIE_ENABLE;
>  
>  static int __init setup_disable_tlbie(char *str)
>  {
> diff --git a/arch/powerpc/platforms/Kconfig.cputype b/arch/powerpc/platforms/Kconfig.cputype
> index 1453ccc900c4..bd2a4e46ab34 100644
> --- a/arch/powerpc/platforms/Kconfig.cputype
> +++ b/arch/powerpc/platforms/Kconfig.cputype
> @@ -449,6 +449,18 @@ config PPC_RADIX_MMU_DEFAULT
>  
>  	  If you're unsure, say Y.
>  
> +config PPC_RADIX_NO_BROADCAST_TLBIE
> +	depends on PPC_RADIX_MMU
> +	help
> +	  Power ISA v3.1 implementations in the Linux Compliancy Subset
> +	  and lower are not required to implement broadcast TLBIE
> +	  instructions, that is, a TLB invalidation instruction
> +	  performed on one CPU is not required to operate on the TLBs
> +	  in all CPUs in the system.  Instead, the kernel does an IPI
> +	  to each relevant CPU to get it to do a local TLBIE instruction.
> +	  Select this option to force global invalidations to be done via
> +	  IPIs unconditionally.

... when using radix MMU. Hash MMU requires broadcast TLBIE.

Nitpicks aside, looks okay to me.

Reviewed-by: Nicholas Piggin <npiggin@gmail.com>

> +
>  config PPC_KERNEL_PREFIXED
>  	depends on PPC_HAVE_PREFIXED_SUPPORT
>  	depends on CC_HAS_PREFIXED
> diff --git a/arch/powerpc/platforms/microwatt/Kconfig b/arch/powerpc/platforms/microwatt/Kconfig
> index 5e41adadac1f..1d5cc1ae3636 100644
> --- a/arch/powerpc/platforms/microwatt/Kconfig
> +++ b/arch/powerpc/platforms/microwatt/Kconfig
> @@ -7,6 +7,7 @@ config PPC_MICROWATT
>  	select PPC_ICP_NATIVE
>  	select PPC_UDBG_16550
>  	select COMMON_CLK
> +	select PPC_RADIX_NO_BROADCAST_TLBIE
>  	help
>            This option enables support for FPGA-based Microwatt implementations.
>