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

From: [email-masked] (Christoffer Dall)
Date: Mon, 13 May 2013 08:46:44 -0700

On Mon, May 13, 2013 at 10:01:57AM +0100, Marc Zyngier wrote:
> On 11/05/13 01:38, Christoffer Dall wrote:
> > On Tue, May 07, 2013 at 05:36:52PM +0100, Marc Zyngier wrote:
> >> 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?
> >>
> > I read the EINVAL to say that you supplied something which is invalid
> > for the software interface and you should fix your user space code.
> 
> Exactly. The code should have checked for the corresponding capability
> before blindly requesting that feature. That's exactly why we have
> capabilities.
> 
> > The fact that you're requesting a feature that your hardware doesn't
> > support is a different thing IMHO.
> 
> Well, if you're allowed to call into this without checking the
> capabilities, then I suggest we remove them, because they are clearly
> superfluous.
> 
I still see a useful distinction, but I don't care enough to keep
arguing.

-Christoffer