Re: [PATCH RFC v2 4/6] KVM: change mark_page_dirty() to handle endian issues explicitly

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On 04/20/2010 02:00 PM, Takuya Yoshikawa wrote:
We are now using generic___set_le_bit() to make dirty bitmaps le.
Though this works well, we have to replace __set_bit() to appropriate
uaccess function to move dirty bitmaps to user space. So this patch
splits generic___set_le_bit() and prepares for that.
+static int __mark_page_dirty(unsigned long nr,
+			     unsigned long *dirty_bitmap)
+#ifdef __BIG_ENDIAN
+	nr = nr ^ BITOP_LE_SWIZZLE;
+	__set_bit(nr, dirty_bitmap);

Why not introduce __set_le_bit_user() along with __set_bit_user()? kvm shouldn't do endian corrections when they can be done in generic code.

  void mark_page_dirty(struct kvm *kvm, gfn_t gfn)
  	struct kvm_memory_slot *memslot;
@@ -1203,11 +1212,8 @@ void mark_page_dirty(struct kvm *kvm, gfn_t gfn)
  	if (memslot&&  memslot->dirty_bitmap) {
  		unsigned long rel_gfn = gfn - memslot->base_gfn;

-		/* avoid RMW */
-		if (!generic_test_le_bit(rel_gfn, memslot->dirty_bitmap)) {
-			generic___set_le_bit(rel_gfn, memslot->dirty_bitmap);
-			memslot->is_dirty = true;
-		}

You're also dropping the RMW avoidance. This is fine, but deserves at least a note in the changelog (or a separate patch).

+		__mark_page_dirty(rel_gfn, memslot->dirty_bitmap);
+		memslot->is_dirty = true;

error compiling committee.c: too many arguments to function

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