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    Subject[PATCH v2 14/14] KVM: SVM: Skip SEV cache flush if no ASIDs have been used
    From
    Skip SEV's expensive WBINVD and DF_FLUSH if there are no SEV ASIDs
    waiting to be reclaimed, e.g. if SEV was never used. This "fixes" an
    issue where the DF_FLUSH fails during hardware teardown if the original
    SEV_INIT failed. Ideally, SEV wouldn't be marked as enabled in KVM if
    SEV_INIT fails, but that's a problem for another day.

    Signed-off-by: Sean Christopherson <seanjc@google.com>
    ---
    arch/x86/kvm/svm/sev.c | 22 ++++++++++------------
    1 file changed, 10 insertions(+), 12 deletions(-)

    diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c
    index 23a4bead4a82..e71bc742d8da 100644
    --- a/arch/x86/kvm/svm/sev.c
    +++ b/arch/x86/kvm/svm/sev.c
    @@ -56,9 +56,14 @@ struct enc_region {
    unsigned long size;
    };

    -static int sev_flush_asids(void)
    +static int sev_flush_asids(int min_asid, int max_asid)
    {
    - int ret, error = 0;
    + int ret, pos, error = 0;
    +
    + /* Check if there are any ASIDs to reclaim before performing a flush */
    + pos = find_next_bit(sev_reclaim_asid_bitmap, max_sev_asid, min_asid);
    + if (pos >= max_asid)
    + return -EBUSY;

    /*
    * DEACTIVATE will clear the WBINVD indicator causing DF_FLUSH to fail,
    @@ -80,14 +85,7 @@ static int sev_flush_asids(void)
    /* Must be called with the sev_bitmap_lock held */
    static bool __sev_recycle_asids(int min_asid, int max_asid)
    {
    - int pos;
    -
    - /* Check if there are any ASIDs to reclaim before performing a flush */
    - pos = find_next_bit(sev_reclaim_asid_bitmap, max_sev_asid, min_asid);
    - if (pos >= max_asid)
    - return false;
    -
    - if (sev_flush_asids())
    + if (sev_flush_asids(min_asid, max_asid))
    return false;

    /* The flush process will flush all reclaimable SEV and SEV-ES ASIDs */
    @@ -1323,10 +1321,10 @@ void sev_hardware_teardown(void)
    if (!sev_enabled)
    return;

    + sev_flush_asids(0, max_sev_asid);
    +
    bitmap_free(sev_asid_bitmap);
    bitmap_free(sev_reclaim_asid_bitmap);
    -
    - sev_flush_asids();
    }

    int sev_cpu_init(struct svm_cpu_data *sd)
    --
    2.30.0.284.gd98b1dd5eaa7-goog
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