Re: [Qemu-arm] [Qemu-devel] [PATCH v2 01/14] target/arm/cpu64: Ensure kvm really supports aarch64=off

[Andrew Jones]

On Wed, Jul 24, 2019 at 02:51:15PM +0200, Auger Eric wrote:
> Hi Drew,
> 
> On 6/25/19 3:34 PM, Andrew Jones wrote:
> > On Tue, Jun 25, 2019 at 11:35:12AM +0200, Auger Eric wrote:
> >> Hi Drew,
> >>
> >> On 6/21/19 6:34 PM, Andrew Jones wrote:
> >>> If -cpu <cpu>,aarch64=off is used then KVM must also be used, and it
> >>> and the host must support running the vcpu in 32-bit mode. Also, if
> s/and it//

"and it and the host" means "and KVM and the host", as 'it' refers to the
last subject, which is KVM. I wanted to point out both the host (machine)
and KVM (version of kernel with KVM) need to support the feature.

> >>> -cpu <cpu>,aarch64=on is used, then it doesn't matter if kvm is
> >>> enabled or not.
> >>>
> >>> Signed-off-by: Andrew Jones <address@hidden>
> >>
> >>
> >>> ---
> >>>  target/arm/cpu64.c   | 12 ++++++------
> >>>  target/arm/kvm64.c   | 11 +++++++++++
> >>>  target/arm/kvm_arm.h | 14 ++++++++++++++
> >>>  3 files changed, 31 insertions(+), 6 deletions(-)
> >>>
> >>> diff --git a/target/arm/cpu64.c b/target/arm/cpu64.c
> >>> index 1901997a0645..946994838d8a 100644
> >>> --- a/target/arm/cpu64.c
> >>> +++ b/target/arm/cpu64.c
> >>> @@ -407,13 +407,13 @@ static void aarch64_cpu_set_aarch64(Object *obj, 
> >>> bool value, Error **errp)
> >>>       * restriction allows us to avoid fixing up functionality that 
> >>> assumes a
> >>>       * uniform execution state like do_interrupt.
> >>>       */> -    if (!kvm_enabled()) {
> >>> -        error_setg(errp, "'aarch64' feature cannot be disabled "
> >>> -                         "unless KVM is enabled");
> >>> -        return;
> >>> -    }
> >>> -
> >>>      if (value == false) {
> >>> +        if (!kvm_enabled() || !kvm_arm_aarch32_supported(CPU(cpu))) {
> >>> +            error_setg(errp, "'aarch64' feature cannot be disabled "
> >>> +                             "unless KVM is enabled and 32-bit EL1 "
> >>> +                             "is supported");
> >>> +            return;
> >>> +        }
> >>>          unset_feature(&cpu->env, ARM_FEATURE_AARCH64);
> >>>      } else {
> >>>          set_feature(&cpu->env, ARM_FEATURE_AARCH64);
> >>> diff --git a/target/arm/kvm64.c b/target/arm/kvm64.c
> >>> index 22d19c9aec6f..45ccda589903 100644
> >>> --- a/target/arm/kvm64.c
> >>> +++ b/target/arm/kvm64.c
> >>> @@ -24,7 +24,9 @@
> >>>  #include "exec/gdbstub.h"
> >>>  #include "sysemu/sysemu.h"
> >>>  #include "sysemu/kvm.h"
> >>> +#include "sysemu/kvm_int.h"
> >>>  #include "kvm_arm.h"
> >>> +#include "hw/boards.h"
> By the way those two new headers are not needed by this patch

Really?

current_machine is defined in hw/boards.h and KVM_STATE is defined
in sysemu/kvm_int.h.

> >>>  #include "internals.h"
> >>>  
> >>>  static bool have_guest_debug;
> >>> @@ -593,6 +595,15 @@ bool 
> >>> kvm_arm_get_host_cpu_features(ARMHostCPUFeatures *ahcf)
> >>>      return true;
> >>>  }
> >>>  
> >>> +bool kvm_arm_aarch32_supported(CPUState *cpu)
> >>> +{
> >>> +    KVMState *s = KVM_STATE(current_machine->accelerator);
> >>> +    int ret;
> >>> +
> >>> +    ret = kvm_check_extension(s, KVM_CAP_ARM_EL1_32BIT);
> >>> +    return ret > 0;
> >> nit: return kvm_check_extension() should be sufficient
> > 
> > Ah yes, I forgot kvm_check_extension() already converts negative
> > error codes to zero. I'll fix that for v3.
> > 
> >>> +}
> >>> +
> >>>  #define ARM_CPU_ID_MPIDR       3, 0, 0, 0, 5
> >>>  
> >>>  int kvm_arch_init_vcpu(CPUState *cs)
> >>> diff --git a/target/arm/kvm_arm.h b/target/arm/kvm_arm.h
> >>> index 2a07333c615f..812125f805a1 100644
> >>> --- a/target/arm/kvm_arm.h
> >>> +++ b/target/arm/kvm_arm.h
> >>> @@ -207,6 +207,15 @@ bool 
> >>> kvm_arm_get_host_cpu_features(ARMHostCPUFeatures *ahcf);
> >>>   */
> >>>  void kvm_arm_set_cpu_features_from_host(ARMCPU *cpu);
> >>>  
> >>> +/**
> >>> + * kvm_arm_aarch32_supported:
> >>> + * @cs: CPUState
> >> use kernel-doc comment style?
> > 
> > This file (kvm_arm.h) doesn't appear to have a super consistent comment
> > style. I see some use @var: for the parameters and some have 'Returns:
> > ...' lines as well. I'm happy to do whatever the maintainers prefer. For
> > now I was just trying to mimic whatever caught my eye.>
> >>> + *
> >>> + * Returns true if the KVM VCPU can enable AArch32 mode and false
> >>> + * otherwise.
> >>> + */
> >>> +bool kvm_arm_aarch32_supported(CPUState *cs);
> >>> +
> >>>  /**
> >>>   * kvm_arm_get_max_vm_ipa_size - Returns the number of bits in the
> >>>   * IPA address space supported by KVM
> >>> @@ -247,6 +256,11 @@ static inline void 
> >>> kvm_arm_set_cpu_features_from_host(ARMCPU *cpu)
> >>>      cpu->host_cpu_probe_failed = true;
> >>>  }
> >>>  
> >>> +static inline bool kvm_arm_aarch32_supported(CPUState *cs)
> >>> +{
> >>> +    return false;
> >>> +}
> >>> +
> >>>  static inline int kvm_arm_get_max_vm_ipa_size(MachineState *ms)
> >>>  {
> >>>      return -ENOENT;
> >>>
> >> Reviewed-by: Eric Auger <address@hidden>

Thanks,
drew