Re: [PATCH v3 13/13] KVM: SVM: Skip SEV cache flush if no ASIDs have been used

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On 1/22/21 2:21 PM, Sean Christopherson wrote:
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@xxxxxxxxxx>

Reviewed-by: Tom Lendacky <thomas.lendacky@xxxxxxx>

---
  arch/x86/kvm/svm/sev.c | 23 +++++++++++------------
  1 file changed, 11 insertions(+), 12 deletions(-)

diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c
index 73da2af1e25d..0a4715e60b88 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 */
@@ -1324,10 +1322,11 @@ 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);
-
-	sev_flush_asids();
  }
int sev_cpu_init(struct svm_cpu_data *sd)




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