linux-kernel - [PATCH 13/13] KVM: SVM: Skip SEV cache flush if no ASIDs have been used

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Date:   Fri,  8 Jan 2021 16:47:14 -0800
From:   Sean Christopherson <seanjc@...gle.com>
To:     Paolo Bonzini <pbonzini@...hat.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Andy Lutomirski <luto@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>
Cc:     Sean Christopherson <seanjc@...gle.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Tom Lendacky <thomas.lendacky@....com>,
        Borislav Petkov <bp@...e.de>,
        Brijesh Singh <brijesh.singh@....com>
Subject: [PATCH 13/13] 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@...gle.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 b4a9c12cf8ce..eb8e4dca4bf2 100644
--- a/arch/x86/kvm/svm/sev.c
+++ b/arch/x86/kvm/svm/sev.c
@@ -51,9 +51,14 @@ 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,
@@ -75,14 +80,7 @@ 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 */
@@ -1316,10 +1314,10 @@ 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