Re: [Xen-devel] [PATCH] xen: arm: setup sane EL1 state while building domain 0.

[Fu Wei <fu.wei@xxxxxxxxxx>]

On 03/17/2014 11:31 PM, Ian Campbell wrote:
> The address translation functions used while building dom0 rely on certain EL1
> state being configured. In particular they are subject to the behaviour of
> SCTLR_EL1.M (stage 1 MMU enabled).
> 
> The Xen (and Linux) boot protocol require that the kernel be entered with the
> MMU disabled but they don't say anything explicitly about exception levels
> other than the one which is active when entering the kernels. Arguably the
> protocol could be said to apply to all exception levels but in any case we
> should cope with this and setup the EL1 state as necessary.
> 
> Fu Wei discovered this when booting Xen from grub.efi over UEFI, it's not
> clear whether grub or UEFI is responsible for leaving stage 1 MMU enabled.
> 
> Reported-by: Fu Wei <fu.wei@xxxxxxxxxx>
> Signed-off-by: Ian Campbell <ian.campbell@xxxxxxxxxx>
> Cc: Fu Wei <fu.wei@xxxxxxxxxx>
> ---
> Fu Wei, can I add your Tested-by here?

Yes, Thanks!
I have tested this with my GRUB binary, it works fine.

> ---
>  xen/arch/arm/domain_build.c |    7 +++++++
>  1 file changed, 7 insertions(+)
> 
> diff --git a/xen/arch/arm/domain_build.c b/xen/arch/arm/domain_build.c
> index 5ca2f15..ea47af5 100644
> --- a/xen/arch/arm/domain_build.c
> +++ b/xen/arch/arm/domain_build.c
> @@ -1022,6 +1022,13 @@ int construct_dom0(struct domain *d)
>  
>      /* The following loads use the domain's p2m */
>      p2m_load_VTTBR(d);
> +    /* Various EL2 operations, such as guest address translations used
> +     * part of the domain build, rely on EL1 state (i.e. whether the
> +     * guest has paging enabled). Since the bootloader may have left
> +     * this state in an arbitrary configuration set it to something
> +     * safe here.
> +     */
> +    WRITE_SYSREG32(SCTLR_GUEST_INIT, SCTLR_EL1);
>  #ifdef CONFIG_ARM_64
>      d->arch.type = kinfo.type;
>      if ( is_pv32_domain(d) )
> 


-- 
Best regards,

Fu Wei
LAVA Engineer From Red Hat
LAVA Team
Linaro.org | Open source software for ARM SoCs
Ph: +86 186 2020 4684 (mobile)
IRC: fuwei
Skype: tekkamanninja
Room 1512, Regus One Corporate Avenue,Level 15,
One Corporate Avenue,222 Hubin Road,Huangpu District,
Shanghai,China 200021 

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