Re: [PATCH v6 19/26] arm64: KVM: Move stashing of x0/x1 into the vector code itself

[Marc Zyngier <marc.zyngier@arm.com>]

On 16/03/18 16:22, Catalin Marinas wrote:
> On Wed, Mar 14, 2018 at 04:50:42PM +0000, Marc Zyngier wrote:
>> All our useful entry points into the hypervisor are starting by
>> saving x0 and x1 on the stack. Let's move those into the vectors
>> by introducing macros that annotate whether a vector is valid or
>> not, thus indicating whether we want to stash registers or not.
>>
>> The only drawback is that we now also stash registers for el2_error,
>> but this should never happen, and we pop them back right at the
>> start of the handling sequence.
>>
>> Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
>> ---
>>  arch/arm64/kvm/hyp/hyp-entry.S | 56 ++++++++++++++++++++++++------------------
>>  1 file changed, 32 insertions(+), 24 deletions(-)
>>
>> diff --git a/arch/arm64/kvm/hyp/hyp-entry.S b/arch/arm64/kvm/hyp/hyp-entry.S
>> index f36464bd57c5..0f62b5f76aa5 100644
>> --- a/arch/arm64/kvm/hyp/hyp-entry.S
>> +++ b/arch/arm64/kvm/hyp/hyp-entry.S
>> @@ -55,7 +55,6 @@ ENTRY(__vhe_hyp_call)
>>  ENDPROC(__vhe_hyp_call)
>>  
>>  el1_sync:				// Guest trapped into EL2
>> -	stp	x0, x1, [sp, #-16]!
>>  
>>  alternative_if_not ARM64_HAS_VIRT_HOST_EXTN
>>  	mrs	x1, esr_el2
>> @@ -137,18 +136,18 @@ alternative_else_nop_endif
>>  	b	__guest_exit
>>  
>>  el1_irq:
>> -	stp     x0, x1, [sp, #-16]!
>>  	ldr	x1, [sp, #16 + 8]
>>  	mov	x0, #ARM_EXCEPTION_IRQ
>>  	b	__guest_exit
>>  
>>  el1_error:
>> -	stp     x0, x1, [sp, #-16]!
>>  	ldr	x1, [sp, #16 + 8]
>>  	mov	x0, #ARM_EXCEPTION_EL1_SERROR
>>  	b	__guest_exit
>>  
>>  el2_error:
>> +	ldp	x0, x1, [sp], #16
>> +
> 
> Nitpick: you don't need a memory access here, just:
> 
> 	add	sp, sp, #16
> 
> (unless el2_error has changed somewhere before this patch)

At this point in the series, I agree. But starting with patch 22, we
start messing with x0 if HARDEN_EL2_VECTORS is valid, meaning we really
need to restore it in order to preserve the guest state.

Thanks,

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