linux-kernel - Re: [PATCH 2/2] KVM: x86: Allow userspace to define what's the microcode version

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Date:   Mon, 27 Nov 2017 09:02:46 +0800
From:   Wanpeng Li <kernellwp@...il.com>
To:     Filippo Sironi <sironi@...zon.de>
Cc:     Paolo Bonzini <pbonzini@...hat.com>,
        Radim Krcmar <rkrcmar@...hat.com>, kvm <kvm@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/2] KVM: x86: Allow userspace to define what's the
 microcode version

2017-11-27 0:41 GMT+08:00 Filippo Sironi <sironi@...zon.de>:
> ... that the guest should see.
> Guest operating systems may check the microcode version to decide whether
> to disable certain features that are known to be buggy up to certain
> microcode versions.  Address the issue by making the microcode version
> that the guest should see settable.
> The rationale for having userspace specifying the microcode version, rather
> than having the kernel picking it, is to ensure consistency for live-migrated
> instances; we don't want them to see a microcode version increase without a
> reset.

Is there a scenario which needs to refresh the microcode in the guest
instead of on the host?

Regards,
Wanpeng Li

>
> Signed-off-by: Filippo Sironi <sironi@...zon.de>
> ---
>  arch/x86/kvm/x86.c       | 23 +++++++++++++++++++++++
>  include/uapi/linux/kvm.h |  3 +++
>  2 files changed, 26 insertions(+)
>
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 925c3e29cad3..741588f27ebc 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -4033,6 +4033,29 @@ long kvm_arch_vm_ioctl(struct file *filp,
>         } u;
>
>         switch (ioctl) {
> +       case KVM_GET_MICROCODE_VERSION: {
> +               r = -EFAULT;
> +               if (copy_to_user(argp,
> +                                &kvm->arch.microcode_version,
> +                                sizeof(kvm->arch.microcode_version)))
> +                       goto out;
> +               break;
> +       }
> +       case KVM_SET_MICROCODE_VERSION: {
> +               u32 microcode_version;
> +
> +               r = -EFAULT;
> +               if (copy_from_user(&microcode_version,
> +                                  argp,
> +                                  sizeof(microcode_version)))
> +                       goto out;
> +               r = -EINVAL;
> +               if (!microcode_version)
> +                       goto out;
> +               kvm->arch.microcode_version = microcode_version;
> +               r = 0;
> +               break;
> +       }
>         case KVM_SET_TSS_ADDR:
>                 r = kvm_vm_ioctl_set_tss_addr(kvm, arg);
>                 break;
> diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
> index 282d7613fce8..e11887758e29 100644
> --- a/include/uapi/linux/kvm.h
> +++ b/include/uapi/linux/kvm.h
> @@ -1192,6 +1192,9 @@ struct kvm_s390_ucas_mapping {
>  #define KVM_S390_UCAS_UNMAP      _IOW(KVMIO, 0x51, struct kvm_s390_ucas_mapping)
>  #define KVM_S390_VCPU_FAULT     _IOW(KVMIO, 0x52, unsigned long)
>
> +#define KVM_GET_MICROCODE_VERSION _IOR(KVMIO, 0x5e, __u32)
> +#define KVM_SET_MICROCODE_VERSION _IOW(KVMIO, 0x5f, __u32)
> +
>  /* Device model IOC */
>  #define KVM_CREATE_IRQCHIP        _IO(KVMIO,   0x60)
>  #define KVM_IRQ_LINE              _IOW(KVMIO,  0x61, struct kvm_irq_level)
> --
> 2.7.4
>