[PATCH 3/5] KVM: mips: Grab MMU lock in kvm_arch_flush_shadow_all()

[James Houghton <jthoughton@google.com>]

kvm_mips_flush_gpa_pt() expects the MMU lock to be held; it is not in
this path.

This can lead to a double-free of page table entries if
kvm_arch_flush_shadow_all() is called twice on the same `kvm`
concurrently; such a scenario is possible.

Cc: stable@vger.kernel.org
Fixes: b62091108633 ("KVM: MIPS: Implement kvm_arch_flush_shadow_all/memslot")
Signed-off-by: James Houghton <jthoughton@google.com>
---
Note: This is compile-tested only!

 arch/mips/kvm/mips.c | 2 ++
 arch/mips/kvm/mmu.c  | 2 ++
 2 files changed, 4 insertions(+)

diff --git a/arch/mips/kvm/mips.c b/arch/mips/kvm/mips.c
index a53abbba43ea..463b6c4aa62c 100644
--- a/arch/mips/kvm/mips.c
+++ b/arch/mips/kvm/mips.c
@@ -180,6 +180,8 @@ long kvm_arch_dev_ioctl(struct file *filp, unsigned int ioctl,
 
 void kvm_arch_flush_shadow_all(struct kvm *kvm)
 {
+	guard(spinlock)(&kvm->mmu_lock);
+
 	/* Flush whole GPA */
 	kvm_mips_flush_gpa_pt(kvm, 0, ~0);
 	kvm_flush_remote_tlbs(kvm);
diff --git a/arch/mips/kvm/mmu.c b/arch/mips/kvm/mmu.c
index d2c3b6b41f18..5045833f8116 100644
--- a/arch/mips/kvm/mmu.c
+++ b/arch/mips/kvm/mmu.c
@@ -269,6 +269,8 @@ static bool kvm_mips_flush_gpa_pgd(pgd_t *pgd, unsigned long start_gpa,
  */
 bool kvm_mips_flush_gpa_pt(struct kvm *kvm, gfn_t start_gfn, gfn_t end_gfn)
 {
+	lockdep_assert_held(&kvm->mmu_lock);
+
 	return kvm_mips_flush_gpa_pgd(kvm->arch.gpa_mm.pgd,
 				      start_gfn << PAGE_SHIFT,
 				      end_gfn << PAGE_SHIFT);
-- 
2.54.0.545.g6539524ca2-goog