[U-Boot] ARM64: How to protect spin-table code from U-Boot?

[Alexander Graf]

On 07.05.16 09:12, Masahiro Yamada wrote:
> Hi.
> 
> I assume the following code in
> arch/arm/cpu/armv8/start.S is for spin-table.
> 
> 
> 
> #ifdef CONFIG_ARMV8_MULTIENTRY
>        branch_if_master x0, x1, master_cpu
> 
>        /*
>         * Slave CPUs
>         */
> slave_cpu:
>        wfe
>        ldr x1, =CPU_RELEASE_ADDR
>        ldr x0, [x1]
>        cbz x0, slave_cpu
>        br x0 /* branch to the given address */
> master_cpu:
>        /* On the master CPU */
> #endif /* CONFIG_ARMV8_MULTIENTRY */
> 
> 
> 
> As Documentation/arm64/booting.txt of Linux says,
> slave CPUs should spin outside of the kernel in a
> reserved area of memory.
> 
> U-Boot generally works on DRAM, so the code for spin-table
> should be reserved in Device Tree.
> 
> Otherwise, the code above and the variable "CPU_RELEASE_ADDR"
> has been destroyed by the kernel by the time slave CPUs are kicked.
> 
> Now, I locally work-around this problem by pre-fetching necessary code
> to the I-cache, but this solution is unstable.
> 
> 
> My question is, is there a solution to protect spin-table code already?
> (or on-going work to solve the problem?)
> 
> One problem specific for U-Boot is that,
> U-Boot relocates itself to the tail of DRAM.
> So, it is difficult to reserve the code statically at the compile time of DT.

I assume your SoC has working EL3? If so, why don't you just provide the
respective PSCI cpu wakeup calls via ATF instead of using spin tables?


Alex