Re: [Xen-devel] [PATCH] xen/arm: Switch OMAP5 secondary cores into hyp mode

[Julien Grall <julien.grall@arm.com>]

Hi Andrew,

On 24/06/2019 13:03, Andrew Cooper wrote:
> On 24/06/2019 12:09, Julien Grall wrote:
>> (+ GSOC mentors and Andre)
>>
>> Hi Denis,
>>
>> Thank you for the patch.
>>
>> First of all, may I ask to CC the other mentors?
>>
>> On 6/21/19 9:02 PM, Denis Obrezkov wrote:
>>> This function allows xen to bring secondary CPU cores into non-secure
>>> HYP mode. This is done by using a Secure Monitor call.
>>>
>>> Signed-off-by: Denis Obrezkov <denisobrezkov@gmail.com>
>>> ---
>>>   xen/arch/arm/arm32/head.S             | 11 ++++++++++-
>>>   xen/arch/arm/platforms/omap5.c        |  5 +++--
>>>   xen/include/asm-arm/platforms/omap5.h |  3 +++
>>>   3 files changed, 16 insertions(+), 3 deletions(-)
>>>
>>> diff --git a/xen/arch/arm/arm32/head.S b/xen/arch/arm/arm32/head.S
>>> index 5f817d473e..120e034934 100644
>>> --- a/xen/arch/arm/arm32/head.S
>>> +++ b/xen/arch/arm/arm32/head.S
>>> @@ -36,6 +36,10 @@
>>>   #include EARLY_PRINTK_INC
>>>   #endif
>>>   +
>>> +#define API_HYP_ENTRY 0x102
>>> +#define AUX_CORE_BOOT0_PA           0x48281800
>>> +
>>
>> I have thought a bit more about the placement of the code. I think it would be 
>> best if it lives in a separate file (maybe platforms/omap5-head.S).
> 
> For something this trivial, it is easy to put straight into omap5.c
> 
> Completely untested, but this ought to work:
> 
> diff --git a/xen/arch/arm/platforms/omap5.c b/xen/arch/arm/platforms/omap5.c
> index 6b5cc15af3..1dcc92d3a4 100644
> --- a/xen/arch/arm/platforms/omap5.c
> +++ b/xen/arch/arm/platforms/omap5.c
> @@ -23,6 +23,16 @@
>   #include <xen/vmap.h>
>   #include <asm/io.h>
>   
> +void omap5_init_secondary(void);
> +asm (
> +".text                            \n\t"
> +"omap5_init_secondary:            \n\t"
> +"        ldr   r12, =0x102        \n\t" /* API_HYP_ENTRY */
> +"        adr   r0, init_secondary \n\t"

You cannot use adr on external address for Arm32. This is because the immediate 
constant needs to have a specific format (see "Modified immediate constants in 
ARM instructions" A5.2.4 in ARM DDI 406C.c).

Instead we would need something like:

omap5_init_secondary:
      ldr r12, =0x102
      adr r0, omap5_hyp
      smc #0
omap5_hyp:
      b   init_secondary

Note similar code would be needed for the stub file.

> +"        smc   #0                 \n\t"
> +"        b     init_secondary     \n\t"
> +);
> +
>   static uint16_t num_den[8][2] = {
>       {         0,          0 },  /* not used */
>       {  26 *  64,  26 *  125 },  /* 12.0 Mhz */
> 
> 
> I personally find this favourable to introducing new stub files.
> 
> Ultimately it is Julien/Stefano's decision, but I'd like to point it out as an 
> option for anyone who is unaware.

Thank you for the suggestion :). This was suggested last week, but no-one came 
back explaining how it could be implemented.

The two are fine with me.

Cheers,

-- 
Julien Grall

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