Re: [PATCH v3 30/32] arm64: KVM: enable initialization of a 32bit vcpu

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

On 24/04/13 00:02, Christoffer Dall wrote:
> On Mon, Apr 08, 2013 at 05:17:32PM +0100, Marc Zyngier wrote:
>> Wire the init of a 32bit vcpu by allowing 32bit modes in pstate,
>> and providing sensible defaults out of reset state.
>>
>> This feature is of course conditioned by the presence of 32bit
>> capability on the physical CPU, and is checked by the KVM_CAP_ARM_EL1_32BIT
>> capability.
>>
>> Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
>> ---
>>  arch/arm64/include/asm/kvm_host.h |  2 +-
>>  arch/arm64/include/uapi/asm/kvm.h |  1 +
>>  arch/arm64/kvm/guest.c            |  6 ++++++
>>  arch/arm64/kvm/reset.c            | 25 ++++++++++++++++++++++++-
>>  include/uapi/linux/kvm.h          |  1 +
>>  5 files changed, 33 insertions(+), 2 deletions(-)
>>
>> diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
>> index d44064d..c3ec107 100644
>> --- a/arch/arm64/include/asm/kvm_host.h
>> +++ b/arch/arm64/include/asm/kvm_host.h
>> @@ -34,7 +34,7 @@
>>  #include <asm/kvm_vgic.h>
>>  #include <asm/kvm_arch_timer.h>
>>  
>> -#define KVM_VCPU_MAX_FEATURES 1
>> +#define KVM_VCPU_MAX_FEATURES 2
>>  
>>  /* We don't currently support large pages. */
>>  #define KVM_HPAGE_GFN_SHIFT(x)	0
>> diff --git a/arch/arm64/include/uapi/asm/kvm.h b/arch/arm64/include/uapi/asm/kvm.h
>> index 5b1110c..5031f42 100644
>> --- a/arch/arm64/include/uapi/asm/kvm.h
>> +++ b/arch/arm64/include/uapi/asm/kvm.h
>> @@ -75,6 +75,7 @@ struct kvm_regs {
>>  #define KVM_VGIC_V2_CPU_SIZE		0x2000
>>  
>>  #define KVM_ARM_VCPU_POWER_OFF		0 /* CPU is started in OFF state */
>> +#define KVM_ARM_VCPU_EL1_32BIT		1 /* CPU running a 32bit VM */
>>  
>>  struct kvm_vcpu_init {
>>  	__u32 target;
>> diff --git a/arch/arm64/kvm/guest.c b/arch/arm64/kvm/guest.c
>> index 47d3729..74ef7d5 100644
>> --- a/arch/arm64/kvm/guest.c
>> +++ b/arch/arm64/kvm/guest.c
>> @@ -93,6 +93,12 @@ static int set_core_reg(struct kvm_vcpu *vcpu, const struct kvm_one_reg *reg)
>>  	if (off == KVM_REG_ARM_CORE_REG(regs.pstate)) {
>>  		unsigned long mode = (*(unsigned long *)valp) & COMPAT_PSR_MODE_MASK;
>>  		switch (mode) {
>> +		case COMPAT_PSR_MODE_USR:
>> +		case COMPAT_PSR_MODE_FIQ:
>> +		case COMPAT_PSR_MODE_IRQ:
>> +		case COMPAT_PSR_MODE_SVC:
>> +		case COMPAT_PSR_MODE_ABT:
>> +		case COMPAT_PSR_MODE_UND:
>>  		case PSR_MODE_EL0t:
>>  		case PSR_MODE_EL1t:
>>  		case PSR_MODE_EL1h:
>> diff --git a/arch/arm64/kvm/reset.c b/arch/arm64/kvm/reset.c
>> index bc33e76..a282d35 100644
>> --- a/arch/arm64/kvm/reset.c
>> +++ b/arch/arm64/kvm/reset.c
>> @@ -35,11 +35,27 @@ static struct kvm_regs default_regs_reset = {
>>  	.regs.pstate = PSR_MODE_EL1h | PSR_A_BIT | PSR_I_BIT | PSR_F_BIT,
>>  };
>>  
>> +static struct kvm_regs default_regs_reset32 = {
>> +	.regs.pstate = (COMPAT_PSR_MODE_SVC | COMPAT_PSR_A_BIT |
>> +			COMPAT_PSR_I_BIT | COMPAT_PSR_F_BIT),
>> +};
>> +
>> +static bool cpu_has_32bit_el1(void)
>> +{
>> +	u64 pfr0;
>> +
>> +	pfr0 = read_cpuid(ID_AA64PFR0_EL1);
>> +	return !!(pfr0 & 0x20);
> 
> again we don't need the double negation

I still hold that it makes things more readable.

>> +}
>> +
>>  int kvm_arch_dev_ioctl_check_extention(long ext)
>>  {
>>  	int r;
>>  
>>  	switch (ext) {
>> +	case KVM_CAP_ARM_EL1_32BIT:
>> +		r = cpu_has_32bit_el1();
>> +		break;
>>  	default:
>>  		r = 0;
>>  	}
>> @@ -62,7 +78,14 @@ int kvm_reset_vcpu(struct kvm_vcpu *vcpu)
>>  
>>  	switch (vcpu->arch.target) {
>>  	default:
>> -		cpu_reset = &default_regs_reset;
>> +		if (test_bit(KVM_ARM_VCPU_EL1_32BIT, vcpu->arch.features)) {
>> +			if (!cpu_has_32bit_el1())
>> +				return -EINVAL;
> 
> I'm not sure EINVAL is appropriate here, the value specified was not
> incorrect, it's that the hardware doesn't support it. ENXIO, ENODEV, and
> add that in Documentation/virtual/kvm/api.txt ?

Not sure. If you ended up here, it means you tried to start a 32bit
guest on a 64bit-only CPU, despite KVM_CAP_ARM_EL1_32BIT telling you
that your CPU is not 32bit capable.

This is clearly an invalid input, isn't it?

Thanks,

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