Re: [Qemu-devel] [PATCH 2/2] ppc: Fix tlb invalidations on 6xx/7xx/7xxx 32-bit processors

[David Gibson <david@gibson.dropbear.id.au>]

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On Mon, Jun 06, 2016 at 07:52:48PM +1000, Benjamin Herrenschmidt wrote:
> The processor only uses some bits of the address and invalidates an
> entire congruence class. Some OSes such as Darwin and HelenOS take
> advantage of this and occasionally invalidate the entire TLB by just
> doing a series of 64 consecutive tlbie for example.
> 
> Our code tries to be too smart here only invalidating a segment
> congruence class (ie, allowing more address bits to be relevant
> in the invalidation), this fails miserably on those OSes.
> 
> Instead don't bother, do like ppc64 and blow the whole tlb when tlbie
> is executed.
> 
> Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

Ugh, this patch too is showing as corrupt for me.  I suspect the
problem is on my end, but I have no idea what, yet.


The concept looks good here, but I don't see much point to keeping the
old broken code around under the #if 0.  I'll rewite accordingly and merge.

> ---
>  target-ppc/mmu_helper.c | 8 ++++++++
>  1 file changed, 8 insertions(+)
> 
> diff --git a/target-ppc/mmu_helper.c b/target-ppc/mmu_helper.c
> index f5c4e69..a5e3878 100644
> --- a/target-ppc/mmu_helper.c
> +++ b/target-ppc/mmu_helper.c
> @@ -1969,6 +1969,11 @@ void ppc_tlb_invalidate_one(CPUPPCState *env, target_ulong addr)
>          /* XXX: this case should be optimized,
>           * giving a mask to tlb_flush_page
>           */
> +        /* This is broken, some CPUs invalidate a whole congruence
> +         * class on an even smaller subset of bits and some OSes take
> +         * advantage of this. Just blow the whole thing away.
> +         */
> +#if 0
>          tlb_flush_page(cs, addr | (0x0 << 28));
>          tlb_flush_page(cs, addr | (0x1 << 28));
>          tlb_flush_page(cs, addr | (0x2 << 28));
> @@ -1985,6 +1990,9 @@ void ppc_tlb_invalidate_one(CPUPPCState *env, target_ulong addr)
>          tlb_flush_page(cs, addr | (0xD << 28));
>          tlb_flush_page(cs, addr | (0xE << 28));
>          tlb_flush_page(cs, addr | (0xF << 28));
> +#else
> +        tlb_flush(cs, 1);
> +#endif
>          break;
>  #if defined(TARGET_PPC64)
>      case POWERPC_MMU_64B:
> 
> 

-- 
David Gibson			| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you.  NOT _the_ _other_
				| _way_ _around_!
http://www.ozlabs.org/~dgibson

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