Re: [PATCH v2 04/40] xen/arm: add an option to define Xen start address for Armv8-R

[Julien Grall <julien@xxxxxxx>]

Hi Penny,

On 13/01/2023 05:28, Penny Zheng wrote:
> From: Wei Chen <wei.chen@xxxxxxx>
>
> On Armv8-A, Xen has a fixed virtual start address (link address
> too) for all Armv8-A platforms. In an MMU based system, Xen can
> map its loaded address to this virtual start address. So, on
> Armv8-A platforms, the Xen start address does not need to be
> configurable. But on Armv8-R platforms, there is no MMU to map
> loaded address to a fixed virtual address and different platforms
> will have very different address space layout. So Xen cannot use
> a fixed physical address on MPU based system and need to have it
> configurable.
>
> In this patch we introduce one Kconfig option for users to define
> the default Xen start address for Armv8-R. Users can enter the
> address in config time, or select the tailored platform config
> file from arch/arm/configs.
>
> And as we introduced Armv8-R platforms to Xen, that means the
> existed Arm64 platforms should not be listed in Armv8-R platform
> list, so we add !ARM_V8R dependency for these platforms.
>
> Signed-off-by: Wei Chen <wei.chen@xxxxxxx>
> Signed-off-by: Jiamei.Xie <jiamei.xie@xxxxxxx>
Your signed-off-by is missing.

> ---
> v1 -> v2:
> 1. Remove the platform header fvp_baser.h.
> 2. Remove the default start address for fvp_baser64.
> 3. Remove the description of default address from commit log.
> 4. Change HAS_MPU to ARM_V8R for Xen start address dependency.
>     No matter Arm-v8r board has MPU or not, it always need to
>     specify the start address.
I don't quite understand the last sentence. Are you saying that it is 
possible to have an ARMv8-R system with an MPU nor a page-table?
> ---
>   xen/arch/arm/Kconfig           |  8 ++++++++
>   xen/arch/arm/platforms/Kconfig | 16 +++++++++++++---
>   2 files changed, 21 insertions(+), 3 deletions(-)
>
> diff --git a/xen/arch/arm/Kconfig b/xen/arch/arm/Kconfig
> index ace7178c9a..c6b6b612d1 100644
> --- a/xen/arch/arm/Kconfig
> +++ b/xen/arch/arm/Kconfig
> @@ -145,6 +145,14 @@ config TEE
>           This option enables generic TEE mediators support. It allows guests
>           to access real TEE via one of TEE mediators implemented in XEN.
>   
> +config XEN_START_ADDRESS
> +       hex "Xen start address: keep default to use platform defined address"
> +       default 0
> +       depends on ARM_V8R
It is still pretty unclear to me what would be the difference between 
HAS_MPU and ARM_V8R.
> +       help
> +         This option allows to set the customized address at which Xen will be
> +         linked on MPU systems. This address must be aligned to a page size.
> +
>   source "arch/arm/tee/Kconfig"
>   
>   config STATIC_SHM
> diff --git a/xen/arch/arm/platforms/Kconfig b/xen/arch/arm/platforms/Kconfig
> index c93a6b2756..0904793a0b 100644
> --- a/xen/arch/arm/platforms/Kconfig
> +++ b/xen/arch/arm/platforms/Kconfig
> @@ -1,6 +1,7 @@
>   choice
>         prompt "Platform Support"
>         default ALL_PLAT
> +       default FVP_BASER if ARM_V8R
>         ---help---
>         Choose which hardware platform to enable in Xen.
>   
> @@ -8,13 +9,14 @@ choice
>   
>   config ALL_PLAT
>         bool "All Platforms"
> +       depends on !ARM_V8R
>         ---help---
>         Enable support for all available hardware platforms. It doesn't
>         automatically select any of the related drivers.
>   
>   config QEMU
>         bool "QEMU aarch virt machine support"
> -       depends on ARM_64
> +       depends on ARM_64 && !ARM_V8R
>         select GICV3
>         select HAS_PL011
>         ---help---
> @@ -23,7 +25,7 @@ config QEMU
>   
>   config RCAR3
>         bool "Renesas RCar3 support"
> -       depends on ARM_64
> +       depends on ARM_64 && !ARM_V8R
>         select HAS_SCIF
>         select IPMMU_VMSA
>         ---help---
> @@ -31,14 +33,22 @@ config RCAR3
>   
>   config MPSOC
>         bool "Xilinx Ultrascale+ MPSoC support"
> -       depends on ARM_64
> +       depends on ARM_64 && !ARM_V8R
>         select HAS_CADENCE_UART
>         select ARM_SMMU
>         ---help---
>         Enable all the required drivers for Xilinx Ultrascale+ MPSoC
>   
> +config FVP_BASER
> +       bool "Fixed Virtual Platform BaseR support"
> +       depends on ARM_V8R
> +       help
> +         Enable platform specific configurations for Fixed Virtual
> +         Platform BaseR
This seems unrelated to this patch.

> +
>   config NO_PLAT
>         bool "No Platforms"
> +       depends on !ARM_V8R
>         ---help---
>         Do not enable specific support for any platform.
>   
Cheers,

--
Julien Grall