[RFC,v1,04/12] KVM: Prepare kvm_is_reserved_pfn() for PG_reserved changes
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Message ID 20191022171239.21487-5-david@redhat.com
State Not Applicable
Headers show
  • mm: Don't mark hotplugged pages PG_reserved (including ZONE_DEVICE)
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Context Check Description
snowpatch_ozlabs/checkpatch fail Test checkpatch on branch powerpc/merge
snowpatch_ozlabs/apply_patch success Successfully applied on branch powerpc/merge (6b450d0404ca83dc131dadffd40c5aa6f7a603af)

Commit Message

David Hildenbrand Oct. 22, 2019, 5:12 p.m. UTC
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. They are treated as
reserved and the page is not touched (e.g., to set it dirty or accessed).

Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: "Radim Krčmář" <rkrcmar@redhat.com>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: KarimAllah Ahmed <karahmed@amazon.de>
Signed-off-by: David Hildenbrand <david@redhat.com>
 virt/kvm/kvm_main.c | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

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diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 66a977472a1c..b233d4129014 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -151,9 +151,15 @@  __weak int kvm_arch_mmu_notifier_invalidate_range(struct kvm *kvm,
 bool kvm_is_reserved_pfn(kvm_pfn_t pfn)
-	if (pfn_valid(pfn))
-		return PageReserved(pfn_to_page(pfn));
+	struct page *page = pfn_to_online_page(pfn);
+	/*
+	 * 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).
+	 */
+	if (page)
+		return PageReserved(page);
 	return true;