linux-kernel - [PATCH 3.16 242/305] kvm: svm: Ensure an IBPB on all affected CPUs when freeing a vmcb

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Message-ID: <lsq.1549201508.609419108@decadent.org.uk>
Date:   Sun, 03 Feb 2019 14:45:08 +0100
From:   Ben Hutchings <ben@...adent.org.uk>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:     akpm@...ux-foundation.org, Denis Kirjanov <kda@...ux-powerpc.org>,
        "Jim Mattson" <jmattson@...gle.com>,
        "Neel Natu" <neelnatu@...gle.com>,
        "Paolo Bonzini" <pbonzini@...hat.com>,
        "Konrad Rzeszutek Wilk" <konrad.wilk@...cle.com>
Subject: [PATCH 3.16 242/305] kvm: svm: Ensure an IBPB on all affected
 CPUs when freeing a vmcb

3.16.63-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Jim Mattson <jmattson@...gle.com>

commit fd65d3142f734bc4376053c8d75670041903134d upstream.

Previously, we only called indirect_branch_prediction_barrier on the
logical CPU that freed a vmcb. This function should be called on all
logical CPUs that last loaded the vmcb in question.

Fixes: 15d45071523d ("KVM/x86: Add IBPB support")
Reported-by: Neel Natu <neelnatu@...gle.com>
Signed-off-by: Jim Mattson <jmattson@...gle.com>
Reviewed-by: Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
[bwh: Backported to 3.16: adjust context]
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 arch/x86/kvm/svm.c | 20 +++++++++++++++-----
 1 file changed, 15 insertions(+), 5 deletions(-)

--- a/arch/x86/kvm/svm.c
+++ b/arch/x86/kvm/svm.c
@@ -1317,21 +1317,31 @@ out:
 	return ERR_PTR(err);
 }
 
+static void svm_clear_current_vmcb(struct vmcb *vmcb)
+{
+	int i;
+
+	for_each_online_cpu(i)
+		cmpxchg(&per_cpu(svm_data, i)->current_vmcb, vmcb, NULL);
+}
+
 static void svm_free_vcpu(struct kvm_vcpu *vcpu)
 {
 	struct vcpu_svm *svm = to_svm(vcpu);
 
+	/*
+	 * The vmcb page can be recycled, causing a false negative in
+	 * svm_vcpu_load(). So, ensure that no logical CPU has this
+	 * vmcb page recorded as its current vmcb.
+	 */
+	svm_clear_current_vmcb(svm->vmcb);
+
 	__free_page(pfn_to_page(svm->vmcb_pa >> PAGE_SHIFT));
 	__free_pages(virt_to_page(svm->msrpm), MSRPM_ALLOC_ORDER);
 	__free_page(virt_to_page(svm->nested.hsave));
 	__free_pages(virt_to_page(svm->nested.msrpm), MSRPM_ALLOC_ORDER);
 	kvm_vcpu_uninit(vcpu);
 	kmem_cache_free(kvm_vcpu_cache, svm);
-	/*
-	 * The vmcb page can be recycled, causing a false negative in
-	 * svm_vcpu_load(). So do a full IBPB now.
-	 */
-	indirect_branch_prediction_barrier();
 }
 
 static void svm_vcpu_load(struct kvm_vcpu *vcpu, int cpu)