[v5,15/15] KVM: SVM: Skip SEV cache flush if no ASIDs have been used
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Message ID 20210422021125.3417167-16-seanjc@google.com
State New
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Series
  • KVM: SVM: Misc SEV cleanups
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Commit Message

Sean Christopherson April 22, 2021, 2:11 a.m. UTC
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 | 23 +++++++++++------------
 1 file changed, 11 insertions(+), 12 deletions(-)

Comments

Paolo Bonzini April 22, 2021, 7:30 a.m. UTC | #1
On 22/04/21 04:11, Sean Christopherson wrote:
> +	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;

There's a tiny bug here which would cause sev_flush_asids to return 0
if there are reclaimed SEV ASIDs and the caller is looking for an SEV-ES
ASID, or vice versa.  The bug used to be in __sev_recycle_asids, you're
just moving the code.

It's not a big deal because sev_asid_new only retries once, but we might
as well fix it:

diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c
index 02b3426a9e39..403c6991e67c 100644
--- a/arch/x86/kvm/svm/sev.c
+++ b/arch/x86/kvm/svm/sev.c
@@ -74,12 +74,13 @@ struct enc_region {
  	unsigned long size;
  };
  
+/* Called with the sev_bitmap_lock held, or on shutdown  */
  static int sev_flush_asids(int min_asid, int max_asid)
  {
  	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);
+	pos = find_next_bit(sev_reclaim_asid_bitmap, max_asid, min_asid);
  	if (pos >= max_asid)
  		return -EBUSY;
  

Paolo

>   	/*
>   	 * DEACTIVATE will clear the WBINVD indicator causing DF_FLUSH to fail,
> @@ -87,14 +92,7 @@ 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 */
> @@ -1846,10 +1844,11 @@ 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)
>

Patch
diff mbox series

diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c
index 5cdfea8b1c47..d65193a4ea17 100644
--- a/arch/x86/kvm/svm/sev.c
+++ b/arch/x86/kvm/svm/sev.c
@@ -58,9 +58,14 @@  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,
@@ -87,14 +92,7 @@  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 */
@@ -1846,10 +1844,11 @@  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)