Re: [PATCH v4 25/28] ARM: decompressor: Remove __hyp_get_vectors usage

Marc Zyngier
2017-03-24T15:26:15Z

On Fri, Mar 24 2017 at 2:34:40 pm GMT, Christoffer Dall <cdall@linaro.org> wrote:
> On Tue, Mar 21, 2017 at 07:20:55PM +0000, Marc Zyngier wrote:
>> When the compressed image needs to be relocated to avoid being
>> overwritten by the decompression process, we need to relocate
>> the hyp vectors as well so that we can find them once the
>> decompression has taken effect.
>>
>> For that, we perform the following calculation:
>> u32 v = __hyp_get_vectors();
>> v += offset;
>> __hyp_set_vectors(v);
>>
>> But we're guaranteed that the initial value of v as returned by
>> __hyp_get_vectors is always __hyp_stub_vectors, because we have
>> just set it by calling __hyp_stub_install.
>>
>> So let's remove the use of __hyp_get_vectors, and directly use
>> __hyp_stub_vectors instead.
>>
>> Acked-by: Russell King <rmk+kernel@armlinux.org.uk>
>> Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
>> ---
>> arch/arm/boot/compressed/head.S | 5 ++++-
>> 1 file changed, 4 insertions(+), 1 deletion(-)
>>
>> diff --git a/arch/arm/boot/compressed/head.S b/arch/arm/boot/compressed/head.S
>> index 9150f9732785..d58bb104c6e8 100644
>> --- a/arch/arm/boot/compressed/head.S
>> +++ b/arch/arm/boot/compressed/head.S
>> @@ -422,7 +422,10 @@ dtb_check_done:
>> cmp r0, #HYP_MODE
>> bne 1f
>>
>> - bl __hyp_get_vectors
>> +0: adr r0, 0b
>> + movw r1, #:lower16:__hyp_stub_vectors - 0b
>> + movt r1, #:upper16:__hyp_stub_vectors - 0b
>> + add r0, r0, r1
>
> nit: you could add a comment explaining what r0 ends up containing,
> because I'm pretty sure this will feel obscure when not read in the
> context of this series with your commit message above.

Sure. This is "Ard's magic stuff" - I'll document that.

Thanks,

M.
--
Jazz is not dead, it just smell funny.