Re: [PATCH] target/ppc/spapr: Update H_GET_CPU_CHARACTERISTICS L1D cache flush bits

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

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On Tue, Jun 15, 2021 at 02:41:07PM +1000, Nicholas Piggin wrote:
> There are several new L1D cache flush bits added to the hcall which reflect
> hardware security features for speculative cache access issues.
> 
> These behaviours are now being specified as negative in order to simplify
> patched kernel compatibility with older firmware (a new problem found in
> existing systems would automatically be vulnerable).

I don't really understand all the consequences of that.  What I need
to know here, is if it's safe to unconditionally enable these bits,
even for older machine types.

> Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
> ---
>  hw/ppc/spapr_hcall.c   | 2 ++
>  include/hw/ppc/spapr.h | 3 +++
>  2 files changed, 5 insertions(+)
> 
> diff --git a/hw/ppc/spapr_hcall.c b/hw/ppc/spapr_hcall.c
> index f25014afda..dfd9df469d 100644
> --- a/hw/ppc/spapr_hcall.c
> +++ b/hw/ppc/spapr_hcall.c
> @@ -1299,6 +1299,8 @@ static target_ulong h_get_cpu_characteristics(PowerPCCPU *cpu,
>          behaviour |= H_CPU_BEHAV_L1D_FLUSH_PR;
>          break;
>      case SPAPR_CAP_FIXED:
> +        behaviour |= H_CPU_BEHAV_NO_L1D_FLUSH_ENTRY;
> +        behaviour |= H_CPU_BEHAV_NO_L1D_FLUSH_UACCESS;
>          break;
>      default: /* broken */
>          assert(safe_cache == SPAPR_CAP_BROKEN);
> diff --git a/include/hw/ppc/spapr.h b/include/hw/ppc/spapr.h
> index f05219f75e..0f25d081a8 100644
> --- a/include/hw/ppc/spapr.h
> +++ b/include/hw/ppc/spapr.h
> @@ -398,10 +398,13 @@ struct SpaprMachineState {
>  #define H_CPU_CHAR_THR_RECONF_TRIG              PPC_BIT(6)
>  #define H_CPU_CHAR_CACHE_COUNT_DIS              PPC_BIT(7)
>  #define H_CPU_CHAR_BCCTR_FLUSH_ASSIST           PPC_BIT(9)
> +
>  #define H_CPU_BEHAV_FAVOUR_SECURITY             PPC_BIT(0)
>  #define H_CPU_BEHAV_L1D_FLUSH_PR                PPC_BIT(1)
>  #define H_CPU_BEHAV_BNDS_CHK_SPEC_BAR           PPC_BIT(2)
>  #define H_CPU_BEHAV_FLUSH_COUNT_CACHE           PPC_BIT(5)
> +#define H_CPU_BEHAV_NO_L1D_FLUSH_ENTRY          PPC_BIT(7)
> +#define H_CPU_BEHAV_NO_L1D_FLUSH_UACCESS        PPC_BIT(8)
>  
>  /* Each control block has to be on a 4K boundary */
>  #define H_CB_ALIGNMENT     4096

-- 
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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