Re: [PATCH 3/6] target/ppc: 4xx don't flush TLB for a newly written software TLB entry

[Cédric Le Goater]

On 1/17/24 16:12, Nicholas Piggin wrote:
> BookE software TLB is implemented by flushing old translations from the
> relevant TCG TLB whenever software TLB entries change. This means a new
> software TLB entry should not have any corresponding cached TCG TLB
> translations, so there is nothing to flush. The exception is multiple
> software TLBs that cover the same address and address space, but that
> is a programming error and results in undefined behaviour, and flushing
> does not give an obviously better outcome in that case either.
>
> Remove the unnecessary flush of a newly written software TLB entry.
>
> Signed-off-by: Nicholas Piggin <npiggin@gmail.com>


Acked-by: Cédric Le Goater <clg@kaod.org>

Thanks,

C.


> ---
>   target/ppc/mmu_helper.c | 7 -------
>   1 file changed, 7 deletions(-)
>
> diff --git a/target/ppc/mmu_helper.c b/target/ppc/mmu_helper.c
> index 949ae87f4f..68632bf54e 100644
> --- a/target/ppc/mmu_helper.c
> +++ b/target/ppc/mmu_helper.c
> @@ -808,13 +808,6 @@ void helper_4xx_tlbwe_hi(CPUPPCState *env, target_ulong 
> entry,
>                     tlb->prot & PAGE_WRITE ? 'w' : '-',
>                     tlb->prot & PAGE_EXEC ? 'x' : '-',
>                     tlb->prot & PAGE_VALID ? 'v' : '-', (int)tlb->PID);
> -    /* Invalidate new TLB (if valid) */
> -    if (tlb->prot & PAGE_VALID) {
> -        qemu_log_mask(CPU_LOG_MMU, "%s: invalidate TLB %d start "
> -                      TARGET_FMT_lx " end " TARGET_FMT_lx "\n", __func__,
> -                      (int)entry, tlb->EPN, tlb->EPN + tlb->size);
> -        ppcemb_tlb_flush(cs, tlb);
> -    }
>   }
>   
>   void helper_4xx_tlbwe_lo(CPUPPCState *env, target_ulong entry,