[PATCH 4 of 5] KVM: ppc: Use a read lock around MMU operations, and release it on error

[Hollis Blanchard]

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 <[EMAIL PROTECTED]>

diff --git a/arch/powerpc/kvm/44x_tlb.c b/arch/powerpc/kvm/44x_tlb.c
--- 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 *vcp
        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;
 
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