• Maxim Levitsky's avatar
    KVM: SVM: fix tsc scaling cache logic · 11d39e8c
    Maxim Levitsky authored
    SVM uses a per-cpu variable to cache the current value of the
    tsc scaling multiplier msr on each cpu.
    
    Commit 1ab9287a
    ("KVM: X86: Add vendor callbacks for writing the TSC multiplier")
    broke this caching logic.
    
    Refactor the code so that all TSC scaling multiplier writes go through
    a single function which checks and updates the cache.
    
    This fixes the following scenario:
    
    1. A CPU runs a guest with some tsc scaling ratio.
    
    2. New guest with different tsc scaling ratio starts on this CPU
       and terminates almost immediately.
    
       This ensures that the short running guest had set the tsc scaling ratio just
       once when it was set via KVM_SET_TSC_KHZ. Due to the bug,
       the per-cpu cache is not updated.
    
    3. The original guest continues to run, it doesn't restore the msr
       value back to its own value, because the cache matches,
       and thus continues to run with a wrong tsc scaling ratio.
    
    Fixes: 1ab9287a ("KVM: X86: Add vendor callbacks for writing the TSC multiplier")
    Signed-off-by: default avatarMaxim Levitsky <mlevitsk@redhat.com>
    Message-Id: <20220606181149.103072-1-mlevitsk@redhat.com>
    Cc: stable@vger.kernel.org
    Signed-off-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
    11d39e8c
svm.c 135 KB