[v3 4/5] KVM: PPC: Book3S HV: retry page migration before erroring-out H_SVM_PAGE_IN

[Ram Pai <linuxram@us.ibm.com>]

The page requested for page-in; sometimes, can have transient
references, and hence cannot migrate immediately. Retry a few times
before returning error.

H_SVM_PAGE_IN interface is enhanced to return H_BUSY if the page is
not in a migratable state.

Cc: Paul Mackerras <paulus@ozlabs.org>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Bharata B Rao <bharata@linux.ibm.com>
Cc: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
Cc: Sukadev Bhattiprolu <sukadev@linux.vnet.ibm.com>
Cc: Laurent Dufour <ldufour@linux.ibm.com>
Cc: Thiago Jung Bauermann <bauerman@linux.ibm.com>
Cc: David Gibson <david@gibson.dropbear.id.au>
Cc: Claudio Carvalho <cclaudio@linux.ibm.com>
Cc: kvm-ppc@vger.kernel.org
Cc: linuxppc-dev@lists.ozlabs.org

Signed-off-by: Ram Pai <linuxram@us.ibm.com>
---
 Documentation/powerpc/ultravisor.rst |  1 +
 arch/powerpc/kvm/book3s_hv_uvmem.c   | 54 +++++++++++++++++++++---------------
 2 files changed, 33 insertions(+), 22 deletions(-)

diff --git a/Documentation/powerpc/ultravisor.rst b/Documentation/powerpc/ultravisor.rst
index d98fc85..638d1a7 100644
--- a/Documentation/powerpc/ultravisor.rst
+++ b/Documentation/powerpc/ultravisor.rst
@@ -1034,6 +1034,7 @@ Return values
 	* H_PARAMETER	if ``guest_pa`` is invalid.
 	* H_P2		if ``flags`` is invalid.
 	* H_P3		if ``order`` of page is invalid.
+	* H_BUSY	if ``page`` is not in a state to pagein
 
 Description
 ~~~~~~~~~~~
diff --git a/arch/powerpc/kvm/book3s_hv_uvmem.c b/arch/powerpc/kvm/book3s_hv_uvmem.c
index 12ed52a..c9bdef6 100644
--- a/arch/powerpc/kvm/book3s_hv_uvmem.c
+++ b/arch/powerpc/kvm/book3s_hv_uvmem.c
@@ -843,7 +843,7 @@ unsigned long kvmppc_h_svm_page_in(struct kvm *kvm, unsigned long gpa,
 	struct vm_area_struct *vma;
 	int srcu_idx;
 	unsigned long gfn = gpa >> page_shift;
-	int ret;
+	int ret, repeat_count = REPEAT_COUNT;
 
 	if (!(kvm->arch.secure_guest & KVMPPC_SECURE_INIT_START))
 		return H_UNSUPPORTED;
@@ -857,34 +857,44 @@ unsigned long kvmppc_h_svm_page_in(struct kvm *kvm, unsigned long gpa,
 	if (flags & H_PAGE_IN_SHARED)
 		return kvmppc_share_page(kvm, gpa, page_shift);
 
-	ret = H_PARAMETER;
 	srcu_idx = srcu_read_lock(&kvm->srcu);
-	down_write(&kvm->mm->mmap_sem);
 
-	start = gfn_to_hva(kvm, gfn);
-	if (kvm_is_error_hva(start))
-		goto out;
-
-	mutex_lock(&kvm->arch.uvmem_lock);
 	/* Fail the page-in request of an already paged-in page */
-	if (kvmppc_gfn_is_uvmem_pfn(gfn, kvm, NULL))
-		goto out_unlock;
+	mutex_lock(&kvm->arch.uvmem_lock);
+	ret = kvmppc_gfn_is_uvmem_pfn(gfn, kvm, NULL);
+	mutex_unlock(&kvm->arch.uvmem_lock);
+	if (ret) {
+		srcu_read_unlock(&kvm->srcu, srcu_idx);
+		return H_PARAMETER;
+	}
 
-	end = start + (1UL << page_shift);
-	vma = find_vma_intersection(kvm->mm, start, end);
-	if (!vma || vma->vm_start > start || vma->vm_end < end)
-		goto out_unlock;
+	do {
+		ret = H_PARAMETER;
+		down_write(&kvm->mm->mmap_sem);
 
-	if (kvmppc_svm_migrate_page(vma, start, end, gpa, kvm, page_shift,
-				true))
-		goto out_unlock;
+		start = gfn_to_hva(kvm, gfn);
+		if (kvm_is_error_hva(start)) {
+			up_write(&kvm->mm->mmap_sem);
+			break;
+		}
 
-	ret = H_SUCCESS;
+		end = start + (1UL << page_shift);
+		vma = find_vma_intersection(kvm->mm, start, end);
+		if (!vma || vma->vm_start > start || vma->vm_end < end) {
+			up_write(&kvm->mm->mmap_sem);
+			break;
+		}
+
+		mutex_lock(&kvm->arch.uvmem_lock);
+		ret = kvmppc_svm_migrate_page(vma, start, end, gpa, kvm, page_shift, true);
+		mutex_unlock(&kvm->arch.uvmem_lock);
+
+		up_write(&kvm->mm->mmap_sem);
+	} while (ret == -2 && repeat_count--);
+
+	if (ret == -2)
+		ret = H_BUSY;
 
-out_unlock:
-	mutex_unlock(&kvm->arch.uvmem_lock);
-out:
-	up_write(&kvm->mm->mmap_sem);
 	srcu_read_unlock(&kvm->srcu, srcu_idx);
 	return ret;
 }
-- 
1.8.3.1