[PATCH v3 01/25] arm64: hyp-stub: Implement HVC_RESET_VECTORS stub hypercall

[Marc Zyngier]

On 21/03/17 17:25, James Morse wrote:
> Hi Catalin,
> 
> On 21/03/17 17:04, Catalin Marinas wrote:
>> On Mon, Mar 06, 2017 at 02:24:34PM +0000, Marc Zyngier wrote:
>>> Let's define a new stub hypercall that resets the HYP configuration
>>> to its default: hyp-stub vectors, and MMU disabled.
>>>
>>> Of course, for the hyp-stub itself, this is a trivial no-op.
>>> Hypervisors will have a bit more work to do.
>>>
>>> Signed-off-by: Marc Zyngier <marc.zyngier at arm.com>
>>> ---
>>>  arch/arm64/include/asm/virt.h |  9 +++++++++
>>>  arch/arm64/kernel/hyp-stub.S  | 13 ++++++++++++-
>>>  2 files changed, 21 insertions(+), 1 deletion(-)
>> [...]
>>> +ENTRY(__hyp_reset_vectors)
>>> +	str	lr, [sp, #-16]!
>>> +	mov	x0, #HVC_RESET_VECTORS
>>> +	hvc	#0
>>> +	ldr	lr, [sp], #16
>>> +	ret
>>> +ENDPROC(__hyp_reset_vectors)
>>
>> Why do we need to specifically preserve lr across the hvc call? Is it
>> corrupted by the EL2 code (if yes, are other caller-saved registers that
>> need preserving)? I don't see something similar in the arch/arm code.
> 
> Kexec on arm64 needed a register to clobber in the hyp-stub's el1_sync code. We
> wanted to preserve all the registers so soft_restart() could look more like a
> function call.

I don't think we need this anymore. Once we enter __cpu_soft_restart(),
there is no turning back. Or am I missing something else?

Thanks,

	M.
-- 
Jazz is not dead. It just smells funny...