Re: [PATCH v4 12/12] KVM: Expose KVM_MEM_PRIVATE

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On 18.01.2022 14:21, Chao Peng wrote:
KVM_MEM_PRIVATE is not exposed by default but architecture code can turn
on it by implementing kvm_arch_private_memory_supported().

Also private memslot cannot be movable and the same file+offset can not
be mapped into different GFNs.

Signed-off-by: Yu Zhang <yu.c.zhang@xxxxxxxxxxxxxxx>
Signed-off-by: Chao Peng <chao.p.peng@xxxxxxxxxxxxxxx>
---
(..)
static bool kvm_check_memslot_overlap(struct kvm_memslots *slots, int id,
-				      gfn_t start, gfn_t end)
+				      struct file *file,
+				      gfn_t start, gfn_t end,
+				      loff_t start_off, loff_t end_off)
  {
  	struct kvm_memslot_iter iter;
+	struct kvm_memory_slot *slot;
+	struct inode *inode;
+	int bkt;
kvm_for_each_memslot_in_gfn_range(&iter, slots, start, end) {
  		if (iter.slot->id != id)
  			return true;
  	}
+ /* Disallow mapping the same file+offset into multiple gfns. */
+	if (file) {
+		inode = file_inode(file);
+		kvm_for_each_memslot(slot, bkt, slots) {
+			if (slot->private_file &&
+			     file_inode(slot->private_file) == inode &&
+			     !(end_off <= slot->private_offset ||
+			       start_off >= slot->private_offset
+					     + (slot->npages >> PAGE_SHIFT)))
+				return true;
+		}
+	}

That's a linear scan of all memslots on each CREATE (and MOVE) operation
with a fd - we just spent more than a year rewriting similar linear scans
into more efficient operations in KVM.

Thanks,
Maciej



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