Re: [Qemu-devel] [PATCH v5 0/4] Add QEMU support for Intel local MCE

[Laszlo Ersek <lersek@redhat.com>]

On 06/22/16 08:56, Haozhong Zhang wrote:
> Changes in v5:
>  * v4 Patch 1&2 are now merged into v5 Patch 1. (Paolo Bonzini)
>  * Add a separate Patch 3 to automatically enable LMCE for "-cpu host"
>    if host does support. (Eduardo Habkost)
>  * Move the sanity check of misconfiguration of LMCE to a separate
>    Patch 4. I'm fine to drop it if it's considered to be
>    unnecessary. (Eduardo Habkost)
>  * Move check of MCG_LMCE_P capability to the existing code in
>    kvm_arch_init_vcpu(). The difference is that if LMCE is not
>    supported by host but MCG_LMCE_P is included in env->mcg_cap,
>    kvm_arch_init_vcpu() return with error instead of just reporting a
>    warning. (Eduardo Habkost)
>  * Fix setting has_msr_feature_control in kvm_arch_init_vcpu(). (Paolo
>    Bonzini)
>  * Fix the type error in fw_cfg file "etc/msr_feature_control".
> 
> Changes in v4:
>  * Abort starting QEMU if lmce option is present but host does support
>    LMCE. (Eduardo Habkost)
>  * Remove setting MSR_IA32_FEATURE_CONTROL, which should be left to
>    guest. (Radim Krčmá, Paolo Bonzini
>  * Adjust error messages in mce_init(). (Boris Petkov)
>  * Move adding option 'lmce' to patch 1. (Eduardo Habkost, Paolo Bonzini)
>  * Adjust LMCE error message in cpu_post_load(). (Eduardo Habkost)
>  * (Patch 3) Add a fw_cfg file 'etc/msr_feature_control' to advise
>    bits should be set in MSR_IA32_FEATURE_CONTROL. (Paolo Bonzini)
>  * Fix SOB chain in patch 1.
> 
> Changes in v3:
>  * LMCE can be enabled only for non-intel guests.
>  * LMCE is disabled by default and a cpu option 'lmce=on/off' is added
>    to explicitly enable/disable LMCE.
>  * LMCE is disabled if KVM does not support (even though 'lmce=on').
>  * VM on LMCE-enabled QEMU can be only migrated to LMCE-enabled QEMU.
>  * MCG_LMCE_P is not included in MCE_CAP_DEF and instead added to
>    env->mcg_cap if LMCE is enabled.
>  * Code style fix.
> 
> This QEMU patch series along with the corresponding KVM patch series
> (sent via another email with title "[PATCH v3 0/3] Add KVM support for
> Intel local MCE") enables Intel local MCE feature for guest.
> 
> Intel Local MCE (LMCE) is a feature on Intel Skylake Server CPU that
> can deliver MCE to a single processor thread instead of broadcasting
> to all threads, which can reduce software's load when processing MCE
> on machines with a large number of processor threads.
> 
> The technical details of LMCE can be found in Intel SDM Vol 3, Chapter
> "Machine-Check Architecture" (search for 'LMCE'). Basically,
>  * The capability of LMCE is indicated by bit 27 (MCG_LMCE_P) of
>    MSR_IA32_MCG_CAP.
>  * LMCE is enabled by setting bit 20 (MSR_IA32_FEATURE_CONTROL_LMCE)
>    of MSR_IA32_FEATURE_CONTROL and bit 0 (MCG_EXT_CTL_LMCE_EN) of
>    MSR_IA32_MCG_EXT_CTL.
>  * Software can determine if a MCE is local to the current processor
>    thread by checking bit 2 (MCG_STATUS_LMCE) of MSR_IA32_MCG_STATUS.
> 
> Ashok Raj (1):
>   target-i386: KVM: add basic Intel LMCE support
> 
> Haozhong Zhang (3):
>   i386: publish advised value of MSR_IA32_FEATURE_CONTROL via fw_cfg
>   target-i386: enable LMCE for '-cpu host' if supported by host
>   target-i386: abort migration if LMCE config mismatch
> 
>  hw/i386/pc.c          | 29 +++++++++++++++++++++++++++++
>  target-i386/cpu.c     | 19 ++++++++++++++++++-
>  target-i386/cpu.h     | 16 ++++++++++++++++
>  target-i386/kvm.c     | 36 +++++++++++++++++++++++++++++++++---
>  target-i386/machine.c | 25 +++++++++++++++++++++++++
>  5 files changed, 121 insertions(+), 4 deletions(-)
> 

How can I test this series?

I'm trying to satisfy the conditions in pc_build_feature_control_file(), so that "etc/msr_feature_control" is created. However, I cannot even trigger

    if (ecx & CPUID_EXT_VMX) {
        feature_control_bits |= FEATURE_CONTROL_VMXON_ENABLED_OUTSIDE_SMX;
    }

I tried various -cpu switches (with and without -enable-kvm); nothing seems to work. When I add "+vmx", QEMU always complains that vmx is not available. Any hints?

(My laptop does support VMX, and it has FEATURE_CONTROL_VMXON_ENABLED_OUTSIDE_SMX set in the corresponding host MSR.)

Thanks
Laszlo