KVM: Don't pre-reserve xarray entries when storing empty/NULL attributesgrafted

Skip the xarray reservation loop when clearing all memory attributes, as
storing NULL only erases the entry and never needs to allocate, so no
reservation (and no cleanup of a failed one) is required in that case.

Suggested-by: Sean Christopherson <seanjc@google.com>
Cc: David Ballesteros <davimaba.v@proton.me>
Signed-off-by: Zeng Chi <zengchi@kylinos.cn>
Link: https://patch.msgid.link/20260921102442.1232375-1-zeng_chi911@163.com
[sean: split to separate patch]
Signed-off-by: Sean Christopherson <seanjc@google.com>

1 files changed, 107 insertions, 0 deletions

diff --git a/include/math-emu/op-8.h b/include/math-emu/op-8.h
new file mode 100644
index 000000000..8b8c05eb8
--- /dev/null
+++ b/include/math-emu/op-8.h
@@ -0,0 +1,107 @@
+/* Software floating-point emulation.
+   Basic eight-word fraction declaration and manipulation.
+   Copyright (C) 1997,1998,1999 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+   Contributed by Richard Henderson (rth@cygnus.com),
+		  Jakub Jelinek (jj@ultra.linux.cz) and
+		  Peter Maydell (pmaydell@chiark.greenend.org.uk).
+                                                         
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Library General Public License as
+   published by the Free Software Foundation; either version 2 of the
+   License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Library General Public License for more details.
+
+   You should have received a copy of the GNU Library General Public
+   License along with the GNU C Library; see the file COPYING.LIB.  If
+   not, write to the Free Software Foundation, Inc.,
+   59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.  */
+
+#ifndef __MATH_EMU_OP_8_H__
+#define __MATH_EMU_OP_8_H__
+
+/* We need just a few things from here for op-4, if we ever need some
+   other macros, they can be added. */
+#define _FP_FRAC_DECL_8(X)	_FP_W_TYPE X##_f[8]
+#define _FP_FRAC_HIGH_8(X)	(X##_f[7])
+#define _FP_FRAC_LOW_8(X)	(X##_f[0])
+#define _FP_FRAC_WORD_8(X,w)	(X##_f[w])
+
+#define _FP_FRAC_SLL_8(X,N)						\
+  do {									\
+    _FP_I_TYPE _up, _down, _skip, _i;					\
+    _skip = (N) / _FP_W_TYPE_SIZE;					\
+    _up = (N) % _FP_W_TYPE_SIZE;					\
+    _down = _FP_W_TYPE_SIZE - _up;					\
+    if (!_up)								\
+      for (_i = 7; _i >= _skip; --_i)					\
+	X##_f[_i] = X##_f[_i-_skip];					\
+    else								\
+      {									\
+	for (_i = 7; _i > _skip; --_i)					\
+	  X##_f[_i] = X##_f[_i-_skip] << _up				\
+		      | X##_f[_i-_skip-1] >> _down;			\
+	X##_f[_i--] = X##_f[0] << _up; 					\
+      }									\
+    for (; _i >= 0; --_i)						\
+      X##_f[_i] = 0;							\
+  } while (0)
+
+#define _FP_FRAC_SRL_8(X,N)						\
+  do {									\
+    _FP_I_TYPE _up, _down, _skip, _i;					\
+    _skip = (N) / _FP_W_TYPE_SIZE;					\
+    _down = (N) % _FP_W_TYPE_SIZE;					\
+    _up = _FP_W_TYPE_SIZE - _down;					\
+    if (!_down)								\
+      for (_i = 0; _i <= 7-_skip; ++_i)					\
+	X##_f[_i] = X##_f[_i+_skip];					\
+    else								\
+      {									\
+	for (_i = 0; _i < 7-_skip; ++_i)				\
+	  X##_f[_i] = X##_f[_i+_skip] >> _down				\
+		      | X##_f[_i+_skip+1] << _up;			\
+	X##_f[_i++] = X##_f[7] >> _down;				\
+      }									\
+    for (; _i < 8; ++_i)						\
+      X##_f[_i] = 0;							\
+  } while (0)
+
+
+/* Right shift with sticky-lsb. 
+ * What this actually means is that we do a standard right-shift,
+ * but that if any of the bits that fall off the right hand side
+ * were one then we always set the LSbit.
+ */
+#define _FP_FRAC_SRS_8(X,N,size)					\
+  do {									\
+    _FP_I_TYPE _up, _down, _skip, _i;					\
+    _FP_W_TYPE _s;							\
+    _skip = (N) / _FP_W_TYPE_SIZE;					\
+    _down = (N) % _FP_W_TYPE_SIZE;					\
+    _up = _FP_W_TYPE_SIZE - _down;					\
+    for (_s = _i = 0; _i < _skip; ++_i)					\
+      _s |= X##_f[_i];							\
+    _s |= X##_f[_i] << _up;						\
+/* s is now != 0 if we want to set the LSbit */				\
+    if (!_down)								\
+      for (_i = 0; _i <= 7-_skip; ++_i)					\
+	X##_f[_i] = X##_f[_i+_skip];					\
+    else								\
+      {									\
+	for (_i = 0; _i < 7-_skip; ++_i)				\
+	  X##_f[_i] = X##_f[_i+_skip] >> _down				\
+		      | X##_f[_i+_skip+1] << _up;			\
+	X##_f[_i++] = X##_f[7] >> _down;				\
+      }									\
+    for (; _i < 8; ++_i)						\
+      X##_f[_i] = 0;							\
+    /* don't fix the LSB until the very end when we're sure f[0] is stable */	\
+    X##_f[0] |= (_s != 0);						\
+  } while (0)
+
+#endif