Re: [Xen-devel] [PATCH for-4.12 1/8] xen/arm: Only set necessary flags when initializing HCR_EL2

[Stefano Stabellini <sstabellini@xxxxxxxxxx>]

On Wed, 28 Nov 2018, Julien Grall wrote:
> Only {A,F,I}MO are necessary to receive interrupts until a guest vCPU is
> loaded.
> 
> The rest have no effect on Xen and it is better to avoid setting them.
> 
> Signed-off-by: Julien Grall <julien.grall@xxxxxxx>
> ---
>  xen/arch/arm/traps.c | 8 ++++++--
>  1 file changed, 6 insertions(+), 2 deletions(-)
> 
> diff --git a/xen/arch/arm/traps.c b/xen/arch/arm/traps.c
> index 88ffeeb480..1eec966299 100644
> --- a/xen/arch/arm/traps.c
> +++ b/xen/arch/arm/traps.c
> @@ -181,8 +181,12 @@ void init_traps(void)
>      WRITE_SYSREG((HCPTR_CP_MASK & ~(HCPTR_CP(10) | HCPTR_CP(11))) | 
> HCPTR_TTA,
>                   CPTR_EL2);
>  
> -    /* Setup hypervisor traps */
> -    WRITE_SYSREG(get_default_hcr_flags(), HCR_EL2);
> +    /*
> +     * Configure HCR_EL2 with the bareminimum to run Xen until a guest
                                     ^ bare minimum

> +     * is scheduled. {A,I,F}MO bits are set to allow EL2 receiving
> +     * interrupts.
> +     */
> +    WRITE_SYSREG(HCR_AMO | HCR_FMO | HCR_IMO, HCR_EL2);
>      isb();
>  }

Reviewed-by: Stefano Stabellini <sstabellini@xxxxxxxxxx>

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