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, 203 insertions, 0 deletions

diff --git a/tools/objtool/trace.c b/tools/objtool/trace.c
new file mode 100644
index 000000000..61c6aa302
--- /dev/null
+++ b/tools/objtool/trace.c
@@ -0,0 +1,203 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * Copyright (c) 2025, Oracle and/or its affiliates.
+ */
+
+#include <objtool/trace.h>
+
+bool trace;
+int trace_depth;
+
+/*
+ * Macros to trace CFI state attributes changes.
+ */
+
+#define TRACE_CFI_ATTR(attr, prev, next, fmt, ...)		\
+({								\
+	if ((prev)->attr != (next)->attr)			\
+		TRACE("%s=" fmt " ", #attr, __VA_ARGS__);	\
+})
+
+#define TRACE_CFI_ATTR_BOOL(attr, prev, next)			\
+	TRACE_CFI_ATTR(attr, prev, next,			\
+		       "%s", (next)->attr ? "true" : "false")
+
+#define TRACE_CFI_ATTR_NUM(attr, prev, next, fmt)		\
+	TRACE_CFI_ATTR(attr, prev, next, fmt, (next)->attr)
+
+#define CFI_REG_NAME_MAXLEN   16
+
+/*
+ * Return the name of a register. Note that the same static buffer
+ * is returned if the name is dynamically generated.
+ */
+static const char *cfi_reg_name(unsigned int reg)
+{
+	static char rname_buffer[CFI_REG_NAME_MAXLEN];
+	const char *rname;
+
+	switch (reg) {
+	case CFI_UNDEFINED:
+		return "<undefined>";
+	case CFI_CFA:
+		return "cfa";
+	case CFI_SP_INDIRECT:
+		return "(sp)";
+	case CFI_BP_INDIRECT:
+		return "(bp)";
+	}
+
+	if (reg < CFI_NUM_REGS) {
+		rname = arch_reg_name[reg];
+		if (rname)
+			return rname;
+	}
+
+	if (snprintf(rname_buffer, CFI_REG_NAME_MAXLEN, "r%d", reg) == -1)
+		return "<error>";
+
+	return (const char *)rname_buffer;
+}
+
+/*
+ * Functions and macros to trace CFI registers changes.
+ */
+
+static void trace_cfi_reg(const char *prefix, int reg, const char *fmt,
+			  int base_prev, int offset_prev,
+			  int base_next, int offset_next)
+{
+	char *rname;
+
+	if (base_prev == base_next && offset_prev == offset_next)
+		return;
+
+	if (prefix)
+		TRACE("%s:", prefix);
+
+	if (base_next == CFI_UNDEFINED) {
+		TRACE("%1$s=<undef> ", cfi_reg_name(reg));
+	} else {
+		rname = strdup(cfi_reg_name(reg));
+		TRACE(fmt, rname, cfi_reg_name(base_next), offset_next);
+		free(rname);
+	}
+}
+
+static void trace_cfi_reg_val(const char *prefix, int reg,
+			      int base_prev, int offset_prev,
+			      int base_next, int offset_next)
+{
+	trace_cfi_reg(prefix, reg, "%1$s=%2$s%3$+d ",
+		      base_prev, offset_prev, base_next, offset_next);
+}
+
+static void trace_cfi_reg_ref(const char *prefix, int reg,
+			      int base_prev, int offset_prev,
+			      int base_next, int offset_next)
+{
+	trace_cfi_reg(prefix, reg, "%1$s=(%2$s%3$+d) ",
+		      base_prev, offset_prev, base_next, offset_next);
+}
+
+#define TRACE_CFI_REG_VAL(reg, prev, next)				\
+	trace_cfi_reg_val(NULL, reg, prev.base, prev.offset,		\
+			  next.base, next.offset)
+
+#define TRACE_CFI_REG_REF(reg, prev, next)				\
+	trace_cfi_reg_ref(NULL, reg, prev.base, prev.offset,		\
+			  next.base, next.offset)
+
+void trace_insn_state(struct instruction *insn, struct insn_state *sprev,
+		      struct insn_state *snext)
+{
+	struct cfi_state *cprev, *cnext;
+	int i;
+
+	if (!memcmp(sprev, snext, sizeof(struct insn_state)))
+		return;
+
+	cprev = &sprev->cfi;
+	cnext = &snext->cfi;
+
+	disas_print_insn(stderr, objtool_disas_ctx, insn,
+			 trace_depth - 1, "state: ");
+
+	/* print registers changes */
+	TRACE_CFI_REG_VAL(CFI_CFA, cprev->cfa, cnext->cfa);
+	for (i = 0; i < CFI_NUM_REGS; i++) {
+		TRACE_CFI_REG_VAL(i, cprev->vals[i], cnext->vals[i]);
+		TRACE_CFI_REG_REF(i, cprev->regs[i], cnext->regs[i]);
+	}
+
+	/* print attributes changes */
+	TRACE_CFI_ATTR_NUM(stack_size, cprev, cnext, "%d");
+	TRACE_CFI_ATTR_BOOL(drap, cprev, cnext);
+	if (cnext->drap) {
+		trace_cfi_reg_val("drap", cnext->drap_reg,
+				  cprev->drap_reg, cprev->drap_offset,
+				  cnext->drap_reg, cnext->drap_offset);
+	}
+	TRACE_CFI_ATTR_BOOL(bp_scratch, cprev, cnext);
+	TRACE_CFI_ATTR_NUM(instr, sprev, snext, "%d");
+	TRACE_CFI_ATTR_NUM(uaccess_stack, sprev, snext, "%u");
+
+	TRACE("\n");
+
+	insn->trace = 1;
+}
+
+void trace_alt_begin(struct instruction *orig_insn, struct alternative *alt,
+		     char *alt_name)
+{
+	struct instruction *alt_insn;
+	char suffix[2];
+
+	alt_insn = alt->insn;
+
+	if (alt->type == ALT_TYPE_EX_TABLE) {
+		/*
+		 * When there is an exception table then the instruction
+		 * at the original location is executed but it can cause
+		 * an exception. In that case, the execution will be
+		 * redirected to the alternative instruction.
+		 *
+		 * The instruction at the original location can have
+		 * instruction alternatives, so we just print the location
+		 * of the instruction that can cause the exception and
+		 * not the instruction itself.
+		 */
+		TRACE_ALT_INFO_NOADDR(orig_insn, "/ ", "%s for instruction at 0x%lx <%s+0x%lx>",
+				      alt_name,
+				      orig_insn->offset, insn_sym(orig_insn)->name,
+				      orig_insn->offset - insn_sym(orig_insn)->offset);
+	} else {
+		TRACE_ALT_INFO_NOADDR(orig_insn, "/ ", "%s", alt_name);
+	}
+
+	if (alt->type == ALT_TYPE_JUMP_TABLE) {
+		/*
+		 * For a jump alternative, if the default instruction is
+		 * a NOP then it is replaced with the jmp instruction,
+		 * otherwise it is replaced with a NOP instruction.
+		 */
+		trace_depth++;
+		if (orig_insn->type == INSN_NOP) {
+			suffix[0] = (orig_insn->len == 5) ? 'q' : '\0';
+			TRACE_ADDR(orig_insn, "jmp%-3s %lx <%s+0x%lx>", suffix,
+				   alt_insn->offset, insn_sym(alt_insn)->name,
+				   alt_insn->offset - insn_sym(alt_insn)->offset);
+		} else {
+			TRACE_ADDR(orig_insn, "nop%d", orig_insn->len);
+			trace_depth--;
+		}
+	}
+}
+
+void trace_alt_end(struct instruction *orig_insn, struct alternative *alt,
+		   char *alt_name)
+{
+	if (alt->type == ALT_TYPE_JUMP_TABLE && orig_insn->type == INSN_NOP)
+		trace_depth--;
+	TRACE_ALT_INFO_NOADDR(orig_insn, "\\ ", "%s", alt_name);
+}