Patch "KVM: PPC: Book3S PR: Exit KVM on failed mapping" has been added to the 4.4-stable tree

This is a note to let you know that I've just added the patch titled

KVM: PPC: Book3S PR: Exit KVM on failed mapping

to the 4.4-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
kvm-ppc-book3s-pr-exit-kvm-on-failed-mapping.patch
and it can be found in the queue-4.4 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Alexey Kardashevskiy <[email protected]>
Date: Fri, 24 Mar 2017 17:48:10 +1100
Subject: KVM: PPC: Book3S PR: Exit KVM on failed mapping

From: Alexey Kardashevskiy <[email protected]>

[ Upstream commit bd9166ffe624000140fc6b606b256df01fc0d060 ]

At the moment kvmppc_mmu_map_page() returns -1 if mmu_hash_ops.hpte_insert() fails for any reason so the page fault handler resumes the guest and it faults on the same address again.

This adds distinction to kvmppc_mmu_map_page() to return -EIO if mmu_hash_ops.hpte_insert() failed for a reason other than full pteg. At the moment only pSeries_lpar_hpte_insert() returns -2 if plpar_pte_enter() failed with a code other than H_PTEG_FULL. Other mmu_hash_ops.hpte_insert() instances can only fail with -1 "full pteg".

With this change, if PR KVM fails to update HPT, it can signal the userspace about this instead of returning to guest and having the very same page fault over and over again.

---
 arch/powerpc/kvm/book3s_64_mmu_host.c |    5 ++++-
 arch/powerpc/kvm/book3s_pr.c          |    6 +++++-
 2 files changed, 9 insertions(+), 2 deletions(-)

@@ -177,12 +177,15 @@ map_again:
 	ret = ppc_md.hpte_insert(hpteg, vpn, hpaddr, rflags, vflags,
 				 hpsize, hpsize, MMU_SEGSIZE_256M);
 
-	if (ret < 0) {
+	if (ret == -1) {
 		/* If we couldn't map a primary PTE, try a secondary */
 		hash = ~hash;
 		vflags ^= HPTE_V_SECONDARY;
 		attempt++;
 		goto map_again;
+	} else if (ret < 0) {
+		r = -EIO;
+		goto out_unlock;
 	} else {
 		trace_kvm_book3s_64_mmu_map(rflags, hpteg,
 					    vpn, hpaddr, orig_pte);

@@ -625,7 +625,11 @@ int kvmppc_handle_pagefault(struct kvm_r
 			kvmppc_mmu_unmap_page(vcpu, &pte);
 		}
 		/* The guest's PTE is not mapped yet. Map on the host */
-		kvmppc_mmu_map_page(vcpu, &pte, iswrite);
+		if (kvmppc_mmu_map_page(vcpu, &pte, iswrite) == -EIO) {
+			/* Exit KVM if mapping failed */
+			run->exit_reason = KVM_EXIT_INTERNAL_ERROR;
+			return RESUME_HOST;
+		}
 		if (data)
 			vcpu->stat.sp_storage++;
 		else if (vcpu->arch.mmu.is_dcbz32(vcpu) &&

Patches currently in stable-queue which might be from [email protected] are

queue-4.4/kvm-ppc-book3s-pr-exit-kvm-on-failed-mapping.patch