Subject: [PATCH] arm/arm64: KVM: detect CPU reset on CPU_PM_EXIT

From: [email-masked] (Marc Zyngier)
Date: Fri, 21 Feb 2014 11:43:19 +0000

On 21/02/14 01:23, Christoffer Dall wrote:
> On Thu, Feb 20, 2014 at 03:26:54PM +0000, Marc Zyngier wrote:
>> Commit 1fcf7ce0c602 (arm: kvm: implement CPU PM notifier) added
>> support for CPU power-management, using a cpu_nofigier to re-init
>> KVM on a CPU that entered CPU idle.
>>
>> The code assumed that a CPU entering idle would actually be powered
>> off, loosing its state entierely, and would then need to be
>> reinitialized. It turns out that this is not always the case, and
>> some HW performs CPU PM without actually killing the core. In this
>> case, we try to reinitialize KVM while it still live. It ends up
>> badly, as reported by Andre Przywara (using a Calxeda Midway):
>>
>> [    3.663897] Kernel panic - not syncing: unexpected prefetch abort in Hyp mode at: 0x685760
>> [    3.663897] unexpected data abort in Hyp mode at: 0xc067d150
>> [    3.663897] unexpected HVC/SVC trap in Hyp mode at: 0xc0901dd0
>>
>> The trick here is to detect if we've been through a full re-init or
>> not by looking at HVBAR (VBAR_EL2 on arm64). This involves
>> implementing the backend for __hyp_get_vectors in the main KVM HYP
>> code (rather small), and checking the return value against the
>> default one when the CPU notifier is called on CPU_PM_EXIT.
> 
> This definitely looks correct and is a good solution, so
> 
> Acked-by: Christoffer Dall <[email-masked]>
> 
> But see my usual request below.
> 
>>
>> Reported-by: Andre Przywara <[email-masked]>
>> Cc: Lorenzo Pieralisi <[email-masked]>
>> Cc: Rob Herring <[email-masked]>
>> Signed-off-by: Marc Zyngier <[email-masked]>
>> ---
>>  arch/arm/kvm/arm.c        | 3 ++-
>>  arch/arm/kvm/interrupts.S | 7 ++++++-
>>  arch/arm64/kvm/hyp.S      | 9 +++++++--
>>  3 files changed, 15 insertions(+), 4 deletions(-)
>>
>> diff --git a/arch/arm/kvm/arm.c b/arch/arm/kvm/arm.c
>> index 1d8248e..bd18bb8 100644
>> --- a/arch/arm/kvm/arm.c
>> +++ b/arch/arm/kvm/arm.c
>> @@ -878,7 +878,8 @@ static int hyp_init_cpu_pm_notifier(struct notifier_block *self,
>>  				    unsigned long cmd,
>>  				    void *v)
>>  {
>> -	if (cmd == CPU_PM_EXIT) {
>> +	if (cmd == CPU_PM_EXIT &&
>> +	    __hyp_get_vectors() == hyp_default_vectors) {
>>  		cpu_init_hyp_mode(NULL);
>>  		return NOTIFY_OK;
>>  	}
>> diff --git a/arch/arm/kvm/interrupts.S b/arch/arm/kvm/interrupts.S
>> index ddc1553..9b0ff68 100644
>> --- a/arch/arm/kvm/interrupts.S
>> +++ b/arch/arm/kvm/interrupts.S
>> @@ -363,6 +363,11 @@ hyp_hvc:
>>  host_switch_to_hyp:
>>  	pop	{r0, r1, r2}
>>  
>> +	/* Check for __hyp_get_vectors */
>> +	cmp	r0, #-1
>> +	mrceq	p15, 4, r0, c12, c0, 0	@ get HVBAR
>> +	beq	1f
>> +
> 
> I hate to be a stickler about this, but I think the comment explaining
> the KVM/ARM Hypervisor ABI needs to be tweaked (it may have been too
> verbose to begin with), but it should be updated at least to specify the
> special-case handling of r0.  I think a small comment somewhere on the
> arm64 part would be similarly nice, but it's not something that should
> hold this patch back.

Good point. I'll add it and repost the patch.

Thanks,

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