[PATCH RFC v1 08/12] powerpc/book3s: Prepare kvmppc_book3s_instantiate_page() for PG_reserved changes

[David Hildenbrand]

Right now, ZONE_DEVICE memory is always set PG_reserved. We want to
change that.

KVM has this weird use case that you can map anything from /dev/mem
into the guest. pfn_valid() is not a reliable check whether the memmap
was initialized and can be touched. pfn_to_online_page() makes sure
that we have an initialized memmap. Note that ZONE_DEVICE memory is
never online (IOW, managed by the buddy).

Switching to pfn_to_online_page() keeps the existing behavior for
PFNs without a memmap and for ZONE_DEVICE memory.

Cc: Paul Mackerras <paulus at ozlabs.org>
Cc: Benjamin Herrenschmidt <benh at kernel.crashing.org>
Cc: Michael Ellerman <mpe at ellerman.id.au>
Signed-off-by: David Hildenbrand <david at redhat.com>
---
 arch/powerpc/kvm/book3s_64_mmu_radix.c | 14 ++++++++------
 1 file changed, 8 insertions(+), 6 deletions(-)

diff --git a/arch/powerpc/kvm/book3s_64_mmu_radix.c b/arch/powerpc/kvm/book3s_64_mmu_radix.c
index 2d415c36a61d..05397c0561fc 100644
--- a/arch/powerpc/kvm/book3s_64_mmu_radix.c
+++ b/arch/powerpc/kvm/book3s_64_mmu_radix.c
@@ -801,12 +801,14 @@ int kvmppc_book3s_instantiate_page(struct kvm_vcpu *vcpu,
 					   writing, upgrade_p);
 		if (is_error_noslot_pfn(pfn))
 			return -EFAULT;
-		page = NULL;
-		if (pfn_valid(pfn)) {
-			page = pfn_to_page(pfn);
-			if (PageReserved(page))
-				page = NULL;
-		}
+		/*
+		 * We treat any pages that are not online (not managed by the
+		 * buddy) as reserved - this includes ZONE_DEVICE pages and
+		 * pages without a memmap (e.g., mapped via /dev/mem).
+		 */
+		page = pfn_to_online_page(pfn);
+		if (page && PageReserved(page))
+			page = NULL;
 	}
 
 	/*
-- 
2.21.0