linux-kernel - RE: [PATCH v2] KVM: Expose the split lock detection feature to guest VM

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Date:   Fri, 6 Jul 2018 08:13:55 +0000
From:   "Liu, Jingqi" <jingqi.liu@...el.com>
To:     Paolo Bonzini <pbonzini@...hat.com>
CC:     "rkrcmar@...hat.com" <rkrcmar@...hat.com>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "hpa@...or.com" <hpa@...or.com>, "x86@...nel.org" <x86@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "Wang, Wei W" <wei.w.wang@...el.com>,
        Robert Hoo <robert.hu@...ux.intel.com>
Subject: RE: [PATCH v2] KVM: Expose the split lock detection feature to
 guest VM

On 04/07/2018 21:37, Paolo Bonzini wrote:
> On 04/07/2018 15:06, Jingqi Liu wrote:
> > A new control bit(bit 29) in the TEST_CTRL MSR will be introduced to
> > enable detection of split locks.
> >
> > When bit 29 of the TEST_CTRL(33H) MSR is set, the processor causes an
> > #AC exception to be issued instead of suppressing LOCK on bus(during
> > split lock access). A previous control bit (bit 31) in this MSR causes
> > the processor to disable LOCK# assertion for split locked accesses
> > when set. When bits 29 and 31 are both set, bit 29 takes precedence.
> >
> > The release document ref below link:
> > https://software.intel.com/sites/default/files/managed/c5/15/\
> > architecture-instruction-set-extensions-programming-reference.pdf
> > This patch has a dependency on https://lkml.org/lkml/2018/5/27/78.
> >
> > Signed-off-by: Jingqi Liu <jingqi.liu@...el.com>
> > ---
> >  arch/x86/include/asm/kvm_host.h |  1 +
> >  arch/x86/kvm/vmx.c              | 77
> +++++++++++++++++++++++++++++++++++++++++
> >  arch/x86/kvm/x86.c              | 10 ++++++
> >  arch/x86/kvm/x86.h              |  5 +++
> >  include/uapi/linux/kvm.h        |  1 +
> >  5 files changed, 94 insertions(+)
> 
> Checking for split lock is done with the MSR_TEST_CTL too, so you should not
> use a capability to expose the availability to KVM userspace.
> Instead you should expose the contents of MSR_TEST_CTL on the host, in a
> similar way to https://marc.info/?l=kvm&m=152998661713547&w=2.
> 
> Please coordinate with Robert Hu on the QEMU patches too, because he's
> working on the infrastructure to use KVM_GET_MSR_FEATURE_INDEX_LIST in
> QEMU.
> 
Hi Paolo,
Thanks  for your review, had synced with Robert.
Need to work out a way, not impact on the old infrastructure.

Thanks
Jingqi

> Thanks,
> 
> Paolo