Re: [Qemu-devel] [PATCH v2] ppc: Fix support for odd MSR combinations

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

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On Sat, Jul 09, 2016 at 01:41:31PM +1000, Benjamin Herrenschmidt wrote:
> MacOS uses an architecturally illegal MSR combination that
> seems nonetheless supported by 32-bit processors, which is
> to have MSR[PR]=1 and one or more of MSR[DR/IR/EE]=0.
> 
> This adds support for it. To work properly we need to also
> properly include support for PR=1,{I,D}R=0 to the MMU index
> used by the qemu TLB.
> 
> Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

Applied to ppc-for-2.7, thanks.


> ---
> 
> v2. Use the correct flags
> 
>  target-ppc/helper_regs.h | 46 ++++++++++++++++++++++------------------------
>  1 file changed, 22 insertions(+), 24 deletions(-)
> 
> diff --git a/target-ppc/helper_regs.h b/target-ppc/helper_regs.h
> index 8fdfa5c..466ad67 100644
> --- a/target-ppc/helper_regs.h
> +++ b/target-ppc/helper_regs.h
> @@ -41,17 +41,19 @@ static inline void hreg_swap_gpr_tgpr(CPUPPCState *env)
>  
>  static inline void hreg_compute_mem_idx(CPUPPCState *env)
>  {
> -    /* This is our encoding for server processors
> +    /* This is our encoding for server processors. The architecture
> +     * specifies that there is no such thing as userspace with
> +     * translation off, however it appears that MacOS does it and
> +     * some 32-bit CPUs support it. Weird...
>       *
>       *   0 = Guest User space virtual mode
>       *   1 = Guest Kernel space virtual mode
> -     *   2 = Guest Kernel space real mode
> -     *   3 = HV User space virtual mode
> -     *   4 = HV Kernel space virtual mode
> -     *   5 = HV Kernel space real mode
> -     *
> -     * The combination PR=1 IR&DR=0 is invalid, we will treat
> -     * it as IR=DR=1
> +     *   2 = Guest User space real mode
> +     *   3 = Guest Kernel space real mode
> +     *   4 = HV User space virtual mode
> +     *   5 = HV Kernel space virtual mode
> +     *   6 = HV User space real mode
> +     *   7 = HV Kernel space real mode
>       *
>       * For BookE, we need 8 MMU modes as follow:
>       *
> @@ -71,20 +73,11 @@ static inline void hreg_compute_mem_idx(CPUPPCState *env)
>          env->immu_idx += msr_gs ? 4 : 0;
>          env->dmmu_idx += msr_gs ? 4 : 0;
>      } else {
> -        /* First calucalte a base value independent of HV */
> -        if (msr_pr != 0) {
> -            /* User space, ignore IR and DR */
> -            env->immu_idx = env->dmmu_idx = 0;
> -        } else {
> -            /* Kernel, setup a base I/D value */
> -            env->immu_idx = msr_ir ? 1 : 2;
> -            env->dmmu_idx = msr_dr ? 1 : 2;
> -        }
> -        /* Then offset it for HV */
> -        if (msr_hv) {
> -            env->immu_idx += 3;
> -            env->dmmu_idx += 3;
> -        }
> +        env->immu_idx = env->dmmu_idx = msr_pr ? 0 : 1;
> +        env->immu_idx += msr_ir ? 0 : 2;
> +        env->dmmu_idx += msr_dr ? 0 : 2;
> +        env->immu_idx += msr_hv ? 4 : 0;
> +        env->dmmu_idx += msr_hv ? 4 : 0;
>      }
>  }
>  
> @@ -136,8 +129,13 @@ static inline int hreg_store_msr(CPUPPCState *env, target_ulong value,
>          /* Change the exception prefix on PowerPC 601 */
>          env->excp_prefix = ((value >> MSR_EP) & 1) * 0xFFF00000;
>      }
> -    /* If PR=1 then EE, IR and DR must be 1 */
> -    if ((value >> MSR_PR) & 1) {
> +    /* If PR=1 then EE, IR and DR must be 1
> +     *
> +     * Note: We only enforce this on 64-bit processors. It appears that
> +     * 32-bit implementations supports PR=1 and EE/DR/IR=0 and MacOS
> +     * exploits it.
> +     */
> +    if ((env->insns_flags & PPC_64B) && ((value >> MSR_PR) & 1)) {
>          value |= (1 << MSR_EE) | (1 << MSR_DR) | (1 << MSR_IR);
>      }
>  #endif
> 
> 

-- 
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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