Re: [PATCH v11 6/6] target-arm: kvm64: Handle SError interrupt for the guest OS

[gengdongjiu]

Hi peter,

> 
> On 18 August 2017 at 15:23, Dongjiu Geng <gengdongjiu@xxxxxxxxxx> wrote:
> > When guest OS happens SError interrupt(SEI), it will trap to host.
> > Host firstly calls memory failure to deal with this error and decide
> > whether it needs to deliver SIGBUS signal to userspace. The advantage
> > that using signal to notify is that it can make the notification
> > method is general, non-KVM user can also use it. when userspace gets
> > this signal and knows this is SError interrupt, it will translate the
> > delivered host VA to PA and record this PA to GHES.
> >
> > Because ARMv8.2 adds an extension to RAS to allow system software
> > insert implicit Error Synchronization Barrier operations to isolate
> > the error and allow passes specified syndrome to guest OS, so after
> > record the CPER, user space calls IOCTL to pass a specified syndrome
> > to KVM, then switch to guest OS, guest OS can use the recorded CPER
> > record and syndrome information to do the recovery.
> >
> > The steps are shown below:
> > 1. translate the host VA to guest OS PA and record this error PA to HEST table.
> > 2. set specified virtual SError syndrome and pass the value to KVM.
> >
> > Signed-off-by: Dongjiu Geng <gengdongjiu@xxxxxxxxxx>
> > Signed-off-by: Quanming Wu <wuquanming@xxxxxxxxxx>
> > ---
> >  linux-headers/linux/kvm.h |  1 +
> >  target/arm/internals.h    |  1 +
> >  target/arm/kvm64.c        | 28 ++++++++++++++++++++++++++++
> >  3 files changed, 30 insertions(+)
> >
> > diff --git a/linux-headers/linux/kvm.h b/linux-headers/linux/kvm.h
> > index 2aa176e..10dfcab 100644
> > --- a/linux-headers/linux/kvm.h
> > +++ b/linux-headers/linux/kvm.h
> > @@ -1356,6 +1356,7 @@ struct kvm_s390_ucas_mapping {
> >  /* Available with KVM_CAP_S390_CMMA_MIGRATION */
> >  #define KVM_S390_GET_CMMA_BITS      _IOWR(KVMIO, 0xb8, struct kvm_s390_cmma_log)
> >  #define KVM_S390_SET_CMMA_BITS      _IOW(KVMIO, 0xb9, struct kvm_s390_cmma_log)
> > +#define KVM_ARM_SEI                 _IO(KVMIO,   0xb10)
> >
> >  #define KVM_DEV_ASSIGN_ENABLE_IOMMU    (1 << 0)
> >  #define KVM_DEV_ASSIGN_PCI_2_3         (1 << 1)
> > diff --git a/target/arm/internals.h b/target/arm/internals.h index
> > fc0ad6d..18b1cbc 100644
> > --- a/target/arm/internals.h
> > +++ b/target/arm/internals.h
> > @@ -237,6 +237,7 @@ enum arm_exception_class {  #define ARM_EL_ISV (1
> > << ARM_EL_ISV_SHIFT)  #define ARM_EL_EC_MASK  ((0x3F) <<
> > ARM_EL_EC_SHIFT)  #define ARM_EL_FSC_TYPE (0x3C)
> > +#define ARM_EL_ISS_MASK ((1 << ARM_EL_IL_SHIFT) - 1)
> >
> >  #define FSC_SEA         (0x10)
> >  #define FSC_SEA_TTW0    (0x14)
> > diff --git a/target/arm/kvm64.c b/target/arm/kvm64.c index
> > d3bdab2..b84cb49 100644
> > --- a/target/arm/kvm64.c
> > +++ b/target/arm/kvm64.c
> > @@ -616,6 +616,22 @@ static int kvm_arm_cpreg_value(ARMCPU *cpu, ptrdiff_t fieldoffset)
> >      return -EINVAL;
> >  }
> >
> > +static int kvm_inject_arm_sei(CPUState *cs) {
> > +    ARMCPU *cpu = ARM_CPU(cs);
> > +    CPUARMState *env = &cpu->env;
> > +
> > +    unsigned long syndrome = env->exception.vaddress;
> > +    /* set virtual SError syndrome */
> > +    if (arm_feature(env, ARM_FEATURE_RAS_EXTENSION)) {
> > +        syndrome = syndrome & ARM_EL_ISS_MASK;
> > +    } else {
> > +        syndrome = 0;
> > +    }
> > +
> > +    return  kvm_vcpu_ioctl(CPU(cpu), KVM_ARM_SEI, &syndrome);
> 
> This looks odd. If we don't have the RAS extension why do we need to do anything at all here ?

This is because Qemu may need to support non-RAS extension as discussed with ARM James before.
That is to say host hardware CPU does not support RAS, but guest supports.
That is under discussion.
When host hardware supports RAS, specify the syndrome to a valid value, otherwise, set it to 0.

> 
> > +}
> > +
> >  /* Inject synchronous external abort */  static int
> > kvm_inject_arm_sea(CPUState *c)  { @@ -1007,6 +1023,15 @@ static bool
> > is_abort_sea(unsigned long syndrome)
> >      }
> >  }
> >
> > +static bool is_abort_sei(unsigned long syndrome) {
> > +    uint8_t ec = ((syndrome & ARM_EL_EC_MASK) >> ARM_EL_EC_SHIFT);
> 
> You don't need to bother masking here -- in other places in QEMU we assume that the EC field is at the top of the word, so just "syndrome >>
> ARM_EL_EC_SHIFT" is sufficient.

OK, thanks for the suggestion.

> 
> > +    if ((ec != EC_SERROR))
> > +        return false;
> > +    else
> > +        return true;
> 
> scripts/checkpatch.pl should tell you that this if needs braces (it's good to get in the habit of running it on all patches; it is not always
> correct, so judgement is required, but it will flag up some common mistakes).
> 
> In this particular case, you should just
>    return ec == EC_SERROR;
> though.

Good suggestion.

> 
> > +}
> > +
> >  void kvm_arch_on_sigbus_vcpu(CPUState *c, int code, void *addr)  {
> >      ram_addr_t ram_addr;
> > @@ -1024,6 +1049,9 @@ void kvm_arch_on_sigbus_vcpu(CPUState *c, int code, void *addr)
> >              if (is_abort_sea(env->exception.syndrome)) {
> >                  ghes_update_guest(ACPI_HEST_NOTIFY_SEA, paddr);
> >                  kvm_inject_arm_sea(c);
> > +            } else if (is_abort_sei(env->exception.syndrome)) {
> > +                ghes_update_guest(ACPI_HEST_NOTIFY_SEI, paddr);
> > +                kvm_inject_arm_sei(c);
> >              }
> >              return;
> >          }
> > --
> > 1.8.3.1
> 
> thanks
> -- PMM