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Date:   Fri, 27 Sep 2019 10:23:32 -0700
From:   Sean Christopherson <sean.j.christopherson@intel.com>
To:     Paolo Bonzini <pbonzini@redhat.com>
Cc:     Jim Mattson <jmattson@google.com>,
        Xiaoyao Li <xiaoyao.li@intel.com>,
        Vitaly Kuznetsov <vkuznets@redhat.com>,
        kvm list <kvm@vger.kernel.org>,
        Eric Hankland <ehankland@google.com>,
        Peter Shier <pshier@google.com>,
        Krish Sadhukhan <krish.sadhukhan@oracle.com>
Subject: Re: [PATCH] kvm: x86: Add Intel PMU MSRs to msrs_to_save[]
Message-ID: <20190927172332.GF25513@linux.intel.com>
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On Fri, Sep 27, 2019 at 07:19:14PM +0200, Paolo Bonzini wrote:
> On 27/09/19 19:14, Sean Christopherson wrote:
> >>
> >> Perhaps we can make all MSRs supported unconditionally if
> >> host_initiated.  For unsupported performance counters it's easy to make
> >> them return 0, and allow setting them to 0, if host_initiated 
> > I don't think we need to go that far.  Allowing any ol' MSR access seems
> > like it would cause more problems than it would solve, e.g. userspace
> > could completely botch something and never know.
> 
> Well, I didn't mean really _all_ MSRs, only those returned by
> KVM_GET_MSR_INDEX_LIST.

Ah, that makes way more sense :-)

> > For the perf MSRs, could we enumerate all arch perf MSRs that are supported
> > by hardware?  That would also be the list of MSRs that host_initiated MSR
> > accesses can touch regardless of guest support.
> 
> Yes, that is easy indeed.  Any ideas about VMX?

Can you elaborate on the problem with VMX MSRs?