KVM: SVM: Skip SEV cache flush if no ASIDs have been used

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>
Message-Id: <20210422021125.3417167-16-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c
index fd3ffc1..a9d8d6a 100644 (file)
--- a/arch/x86/kvm/svm/sev.c
+++ b/arch/x86/kvm/svm/sev.c
@@ -74,9 +74,15 @@ struct enc_region {
        unsigned long size;
 };
 
-static int sev_flush_asids(void)
+/* Called with the sev_bitmap_lock held, or on shutdown  */
+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_asid, min_asid);
+       if (pos >= max_asid)
+               return -EBUSY;
 
        /*
         * DEACTIVATE will clear the WBINVD indicator causing DF_FLUSH to fail,
@@ -103,14 +109,7 @@ static inline bool is_mirroring_enc_context(struct kvm *kvm)
 /* 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 */
@@ -1897,12 +1896,14 @@ void sev_hardware_teardown(void)
        if (!sev_enabled)
                return;
 
+       /* No need to take sev_bitmap_lock, all VMs have been destroyed. */
+       sev_flush_asids(0, max_sev_asid);
+
        bitmap_free(sev_asid_bitmap);
        bitmap_free(sev_reclaim_asid_bitmap);
+
        misc_cg_set_capacity(MISC_CG_RES_SEV, 0);
        misc_cg_set_capacity(MISC_CG_RES_SEV_ES, 0);
-
-       sev_flush_asids();
 }
 
 int sev_cpu_init(struct svm_cpu_data *sd)