Re: [Qemu-devel] [PATCH 05/17] ppc: Fix hreg_store_msr() so that non-HV mode cannot alter MSR:HV

[Thomas Huth <thuth@redhat.com>]

On 14.03.2016 17:56, Cédric Le Goater wrote:
> From: Benjamin Herrenschmidt <benh@kernel.crashing.org>
> 
> This helper is only used by the various instructions that can alter
> MSR and not interrupts. Add a comment to that effect to the interrupt
> code as well in case somebody wants to change this
> 
> Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
> Reviewed-by: David Gibson <david@gibson.dropbear.id.au>
> ---
>  target-ppc/excp_helper.c | 8 ++++++--
>  target-ppc/helper_regs.h | 4 ++--
>  2 files changed, 8 insertions(+), 4 deletions(-)
> 
> diff --git a/target-ppc/excp_helper.c b/target-ppc/excp_helper.c
> index c890853d861b..37d4721db63b 100644
> --- a/target-ppc/excp_helper.c
> +++ b/target-ppc/excp_helper.c
> @@ -666,8 +666,12 @@ static inline void powerpc_excp(PowerPCCPU *cpu, int excp_model, int excp)
>          }
>      }
>  #endif
> -    /* XXX: we don't use hreg_store_msr here as already have treated
> -     *      any special case that could occur. Just store MSR and update hflags
> +    /* We don't use hreg_store_msr here as already have treated
> +     * any special case that could occur. Just store MSR and update hflags
> +     *
> +     * Note: We *MUST* not use hreg_store_msr() as-is anyway because it
> +     * will prevent setting of the HV bit which some exceptions might need
> +     * to do.
>       */
>      env->msr = new_msr & env->msr_mask;
>      hreg_compute_hflags(env);
> diff --git a/target-ppc/helper_regs.h b/target-ppc/helper_regs.h
> index 271fddf17f0a..844240d1a755 100644
> --- a/target-ppc/helper_regs.h
> +++ b/target-ppc/helper_regs.h
> @@ -75,8 +75,8 @@ static inline int hreg_store_msr(CPUPPCState *env, target_ulong value,
>      excp = 0;
>      value &= env->msr_mask;
>  #if !defined(CONFIG_USER_ONLY)
> -    if (!alter_hv) {
> -        /* mtmsr cannot alter the hypervisor state */
> +    /* Neither mtmsr nor guest state can alter HV */
> +    if (!alter_hv || !(env->msr & MSR_HVB)) {
>          value &= ~MSR_HVB;
>          value |= env->msr & MSR_HVB;
>      }

Reviewed-by: Thomas Huth <thuth@redhat.com>