• Alexander Graf's avatar
    KVM: x86: Allow deflecting unknown MSR accesses to user space · 1ae09954
    Alexander Graf authored
    MSRs are weird. Some of them are normal control registers, such as EFER.
    Some however are registers that really are model specific, not very
    interesting to virtualization workloads, and not performance critical.
    Others again are really just windows into package configuration.
    
    Out of these MSRs, only the first category is necessary to implement in
    kernel space. Rarely accessed MSRs, MSRs that should be fine tunes against
    certain CPU models and MSRs that contain information on the package level
    are much better suited for user space to process. However, over time we have
    accumulated a lot of MSRs that are not the first category, but still handled
    by in-kernel KVM code.
    
    This patch adds a generic interface to handle WRMSR and RDMSR from user
    space. With this, any future MSR that is part of the latter categories can
    be handled in user space.
    
    Furthermore, it allows us to replace the existing "ignore_msrs" logic with
    something that applies per-VM rather than on the full system. That way you
    can run productive VMs in parallel to experimental ones where you don't care
    about proper MSR handling.
    Signed-off-by: default avatarAlexander Graf <graf@amazon.com>
    Reviewed-by: default avatarJim Mattson <jmattson@google.com>
    
    Message-Id: <20200925143422.21718-3-graf@amazon.com>
    Signed-off-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
    1ae09954
api.rst 204 KB