Re: [PATCH v4 05/28] arm64: KVM: Implement HVC_RESET_VECTORS stub hypercall in the init code

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

On 24/03/17 14:33, Christoffer Dall wrote:
> On Tue, Mar 21, 2017 at 07:20:35PM +0000, Marc Zyngier wrote:
>> In order to restore HYP mode to its original condition, KVM currently
>> implements __kvm_hyp_reset(). As we're moving towards a hyp-stub
>> defined API, it becomes necessary to implement HVC_RESET_VECTORS.
>>
>> This patch adds the HVC_RESET_VECTORS hypercall to the KVM init
>> code, which so far lacked any form of hypercall support.
>>
>> Reviewed-by: James Morse <james.morse@arm.com>
>> Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
>> ---
>>  arch/arm64/kvm/hyp-init.S | 12 ++++++++++++
>>  1 file changed, 12 insertions(+)
>>
>> diff --git a/arch/arm64/kvm/hyp-init.S b/arch/arm64/kvm/hyp-init.S
>> index 6b29d3d9e1f2..6cf98ccd10f2 100644
>> --- a/arch/arm64/kvm/hyp-init.S
>> +++ b/arch/arm64/kvm/hyp-init.S
>> @@ -22,6 +22,7 @@
>>  #include <asm/kvm_mmu.h>
>>  #include <asm/pgtable-hwdef.h>
>>  #include <asm/sysreg.h>
>> +#include <asm/virt.h>
>>  
>>  	.text
>>  	.pushsection	.hyp.idmap.text, "ax"
>> @@ -58,6 +59,9 @@ __invalid:
>>  	 * x2: HYP vectors
>>  	 */
>>  __do_hyp_init:
>> +	/* Check for a stub HVC call */
>> +	cmp	x0, #HVC_STUB_HCALL_NR
>> +	b.lo	__kvm_handle_stub_hvc
>>  
>>  	msr	ttbr0_el2, x0
>>  
>> @@ -119,6 +123,9 @@ __do_hyp_init:
>>  	eret
>>  ENDPROC(__kvm_hyp_init)
>>  
>> +ENTRY(__kvm_handle_stub_hvc)
>> +	cmp	x0, #HVC_RESET_VECTORS
>> +	b.ne	1f
>>  	/*
>>  	 * Reset kvm back to the hyp stub.
>>  	 */
>> @@ -133,9 +140,14 @@ ENTRY(__kvm_hyp_reset)
>>  	/* Install stub vectors */
>>  	adr_l	x0, __hyp_stub_vectors
>>  	msr	vbar_el2, x0
>> +	b	exit
>>  
>> +1:	mov	x0, #-1
> 
> nit: do we have the -1 return value documented somewhere and should we
> define it as HVC_SUB_ERR_RETURN or something like that?

Indeed, this is something that is a bit dodgy. arm64 returns
ARM_EXCEPTION_HYP_GONE, which is really a KVM exception code (and isn't
-1 either). I'll try to tighten this up a bit.

Thanks,

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