[PATCH] svm: Add mutex_lock to protect apic_access_page_done on AMD systems

[Suthikulpanit, Suravee]

From: Wei Wang <wa...@amazon.de>

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 <wa...@amazon.de>
Signed-off-by: Amadeusz Juskowiak <aj...@amazon.de>
Signed-off-by: Julian Stecklina <jstec...@amazon.de>
Signed-off-by: Suravee Suthikulpanit <suravee.suthikulpa...@amd.com>
---
 arch/x86/kvm/svm.c | 19 +++++++++++--------
 1 file changed, 11 insertions(+), 8 deletions(-)

diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
index d96092b35936..8be1718fed1d 100644
--- a/arch/x86/kvm/svm.c
+++ b/arch/x86/kvm/svm.c
@@ -1658,20 +1658,23 @@ static u64 *avic_get_physical_id_entry(struct kvm_vcpu 
*vcpu,
 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)
-- 
2.17.1