KVM: ppc: Use a read lock around MMU operations, and release it on error

gfn_to_page() and kvm_release_page_clean() are called from other contexts with
mmap_sem locked only for reading.

Signed-off-by: Hollis Blanchard <hollisb@us.ibm.com>
Signed-off-by: Avi Kivity <avi@qumranet.com>

1 files changed, 3 insertions, 2 deletions

diff --git a/arch/powerpc/kvm/44x_tlb.c b/arch/powerpc/kvm/44x_tlb.c
index aa649c7db99b..1c48d6164bd5 100644
--- a/arch/powerpc/kvm/44x_tlb.c
+++ b/arch/powerpc/kvm/44x_tlb.c
@@ -142,18 +142,19 @@ void kvmppc_mmu_map(struct kvm_vcpu *vcpu, u64 gvaddr, gfn_t gfn, u64 asid,
         stlbe = &vcpu->arch.shadow_tlb[victim];
 
         /* Get reference to new page. */
-        down_write(&current->mm->mmap_sem);
+        down_read(&current->mm->mmap_sem);
         new_page = gfn_to_page(vcpu->kvm, gfn);
         if (is_error_page(new_page)) {
                 printk(KERN_ERR "Couldn't get guest page!\n");
                 kvm_release_page_clean(new_page);
+                up_read(&current->mm->mmap_sem);
                 return;
         }
         hpaddr = page_to_phys(new_page);
 
         /* Drop reference to old page. */
         kvmppc_44x_shadow_release(vcpu, victim);
-        up_write(&current->mm->mmap_sem);
+        up_read(&current->mm->mmap_sem);
 
         vcpu->arch.shadow_pages[victim] = new_page;