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

From: [email-masked] (Marc Zyngier)
Date: Tue, 07 May 2013 17:36:52 +0100

On 24/04/13 18:17, Christoffer Dall wrote:
> On Wed, Apr 24, 2013 at 6:49 AM, Marc Zyngier <[email-masked]> wrote:
>> 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 <[email-masked]>
>>>> ---
>>>>  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?
>>
> check the API documentation for this ioctl, I don't think that's the
> type of invalid input meant when describing the meaning of EINVAL. If
> you feel strongly about it of course it's no big deal, but I think
> EINVAL is so overloaded anyway that telling the user something more
> specific would be great, but I'll leave it up to you.

[bit late on this one...]

Here's what the documentation says:
<quote>
4.77 KVM_ARM_VCPU_INIT

Capability: basic
Architectures: arm, arm64
Type: vcpu ioctl
Parameters: struct struct kvm_vcpu_init (in)
Returns: 0 on success; -1 on error
Errors:
  EINVAL:    the target is unknown, or the combination of features is invalid.
  ENOENT:    a features bit specified is unknown.
</quote>

When this call fails, it is because you've requested a feature
that is invalid for this CPU. To me, that exactly fits the
EINVAL entry copied above.

Or am I completely misunderstanding it?

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