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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org, Wei Wang <wawei@amazon.de>,
        Amadeusz Juskowiak <ajusk@amazon.de>,
        Julian Stecklina <jsteckli@amazon.de>,
        Suravee Suthikulpanit <suravee.suthikulpanit@amd.com>,
        Joerg Roedel <jroedel@suse.de>,
        Paolo Bonzini <pbonzini@redhat.com>
Subject: [PATCH 4.9 026/101] svm: Add mutex_lock to protect apic_access_page_done on AMD systems
Date:   Thu,  6 Dec 2018 15:38:25 +0100
Message-Id: <20181206143013.086132381@linuxfoundation.org>
In-Reply-To: <20181206143011.174892052@linuxfoundation.org>
References: <20181206143011.174892052@linuxfoundation.org>
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4.9-stable review patch.  If anyone has any objections, please let me know.

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

From: Wei Wang <wawei@amazon.de>

commit 30510387a5e45bfcf8190e03ec7aa15b295828e2 upstream.

There is a race condition when accessing kvm->arch.apic_access_page_done.
Due to it, x86_set_memory_region will fail when creating the second vcpu
for a svm guest.

Add a mutex_lock to serialize the accesses to apic_access_page_done.
This lock is also used by vmx for the same purpose.

Signed-off-by: Wei Wang <wawei@amazon.de>
Signed-off-by: Amadeusz Juskowiak <ajusk@amazon.de>
Signed-off-by: Julian Stecklina <jsteckli@amazon.de>
Signed-off-by: Suravee Suthikulpanit <suravee.suthikulpanit@amd.com>
Reviewed-by: Joerg Roedel <jroedel@suse.de>
Cc: stable@vger.kernel.org
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 arch/x86/kvm/svm.c |   19 +++++++++++--------
 1 file changed, 11 insertions(+), 8 deletions(-)

--- a/arch/x86/kvm/svm.c
+++ b/arch/x86/kvm/svm.c
@@ -1333,20 +1333,23 @@ static u64 *avic_get_physical_id_entry(s
 static int avic_init_access_page(struct kvm_vcpu *vcpu)
 {
 	struct kvm *kvm = vcpu->kvm;
-	int ret;
+	int ret = 0;
 
+	mutex_lock(&kvm->slots_lock);
 	if (kvm->arch.apic_access_page_done)
-		return 0;
+		goto out;
 
-	ret = x86_set_memory_region(kvm,
-				    APIC_ACCESS_PAGE_PRIVATE_MEMSLOT,
-				    APIC_DEFAULT_PHYS_BASE,
-				    PAGE_SIZE);
+	ret = __x86_set_memory_region(kvm,
+				      APIC_ACCESS_PAGE_PRIVATE_MEMSLOT,
+				      APIC_DEFAULT_PHYS_BASE,
+				      PAGE_SIZE);
 	if (ret)
-		return ret;
+		goto out;
 
 	kvm->arch.apic_access_page_done = true;
-	return 0;
+out:
+	mutex_unlock(&kvm->slots_lock);
+	return ret;
 }
 
 static int avic_init_backing_page(struct kvm_vcpu *vcpu)