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, 233 insertions, 0 deletions

diff --git a/arch/alpha/lib/fpreg.c b/arch/alpha/lib/fpreg.c
new file mode 100644
index 000000000..3d3216504
--- /dev/null
+++ b/arch/alpha/lib/fpreg.c
@@ -0,0 +1,233 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * arch/alpha/lib/fpreg.c
+ *
+ * (C) Copyright 1998 Linus Torvalds
+ */
+
+#include <linux/compiler.h>
+#include <linux/export.h>
+#include <linux/preempt.h>
+#include <asm/fpu.h>
+#include <asm/thread_info.h>
+
+#if defined(CONFIG_ALPHA_EV6) || defined(CONFIG_ALPHA_EV67)
+#define STT(reg,val)  asm volatile ("ftoit $f"#reg",%0" : "=r"(val));
+#else
+#define STT(reg,val)  asm volatile ("stt $f"#reg",%0" : "=m"(val));
+#endif
+
+unsigned long
+alpha_read_fp_reg (unsigned long reg)
+{
+	unsigned long val;
+
+	if (unlikely(reg >= 32))
+		return 0;
+	preempt_disable();
+	if (current_thread_info()->status & TS_SAVED_FP)
+		val = current_thread_info()->fp[reg];
+	else switch (reg) {
+	      case  0: STT( 0, val); break;
+	      case  1: STT( 1, val); break;
+	      case  2: STT( 2, val); break;
+	      case  3: STT( 3, val); break;
+	      case  4: STT( 4, val); break;
+	      case  5: STT( 5, val); break;
+	      case  6: STT( 6, val); break;
+	      case  7: STT( 7, val); break;
+	      case  8: STT( 8, val); break;
+	      case  9: STT( 9, val); break;
+	      case 10: STT(10, val); break;
+	      case 11: STT(11, val); break;
+	      case 12: STT(12, val); break;
+	      case 13: STT(13, val); break;
+	      case 14: STT(14, val); break;
+	      case 15: STT(15, val); break;
+	      case 16: STT(16, val); break;
+	      case 17: STT(17, val); break;
+	      case 18: STT(18, val); break;
+	      case 19: STT(19, val); break;
+	      case 20: STT(20, val); break;
+	      case 21: STT(21, val); break;
+	      case 22: STT(22, val); break;
+	      case 23: STT(23, val); break;
+	      case 24: STT(24, val); break;
+	      case 25: STT(25, val); break;
+	      case 26: STT(26, val); break;
+	      case 27: STT(27, val); break;
+	      case 28: STT(28, val); break;
+	      case 29: STT(29, val); break;
+	      case 30: STT(30, val); break;
+	      case 31: STT(31, val); break;
+	}
+	preempt_enable();
+	return val;
+}
+EXPORT_SYMBOL(alpha_read_fp_reg);
+
+#if defined(CONFIG_ALPHA_EV6) || defined(CONFIG_ALPHA_EV67)
+#define LDT(reg,val)  asm volatile ("itoft %0,$f"#reg : : "r"(val));
+#else
+#define LDT(reg,val)  asm volatile ("ldt $f"#reg",%0" : : "m"(val));
+#endif
+
+void
+alpha_write_fp_reg (unsigned long reg, unsigned long val)
+{
+	if (unlikely(reg >= 32))
+		return;
+
+	preempt_disable();
+	if (current_thread_info()->status & TS_SAVED_FP) {
+		current_thread_info()->status |= TS_RESTORE_FP;
+		current_thread_info()->fp[reg] = val;
+	} else switch (reg) {
+	      case  0: LDT( 0, val); break;
+	      case  1: LDT( 1, val); break;
+	      case  2: LDT( 2, val); break;
+	      case  3: LDT( 3, val); break;
+	      case  4: LDT( 4, val); break;
+	      case  5: LDT( 5, val); break;
+	      case  6: LDT( 6, val); break;
+	      case  7: LDT( 7, val); break;
+	      case  8: LDT( 8, val); break;
+	      case  9: LDT( 9, val); break;
+	      case 10: LDT(10, val); break;
+	      case 11: LDT(11, val); break;
+	      case 12: LDT(12, val); break;
+	      case 13: LDT(13, val); break;
+	      case 14: LDT(14, val); break;
+	      case 15: LDT(15, val); break;
+	      case 16: LDT(16, val); break;
+	      case 17: LDT(17, val); break;
+	      case 18: LDT(18, val); break;
+	      case 19: LDT(19, val); break;
+	      case 20: LDT(20, val); break;
+	      case 21: LDT(21, val); break;
+	      case 22: LDT(22, val); break;
+	      case 23: LDT(23, val); break;
+	      case 24: LDT(24, val); break;
+	      case 25: LDT(25, val); break;
+	      case 26: LDT(26, val); break;
+	      case 27: LDT(27, val); break;
+	      case 28: LDT(28, val); break;
+	      case 29: LDT(29, val); break;
+	      case 30: LDT(30, val); break;
+	      case 31: LDT(31, val); break;
+	}
+	preempt_enable();
+}
+EXPORT_SYMBOL(alpha_write_fp_reg);
+
+#if defined(CONFIG_ALPHA_EV6) || defined(CONFIG_ALPHA_EV67)
+#define STS(reg,val)  asm volatile ("ftois $f"#reg",%0" : "=r"(val));
+#else
+#define STS(reg,val)  asm volatile ("sts $f"#reg",%0" : "=m"(val));
+#endif
+
+unsigned long
+alpha_read_fp_reg_s (unsigned long reg)
+{
+	unsigned long val;
+
+	if (unlikely(reg >= 32))
+		return 0;
+
+	preempt_disable();
+	if (current_thread_info()->status & TS_SAVED_FP) {
+		LDT(0, current_thread_info()->fp[reg]);
+		STS(0, val);
+	} else switch (reg) {
+	      case  0: STS( 0, val); break;
+	      case  1: STS( 1, val); break;
+	      case  2: STS( 2, val); break;
+	      case  3: STS( 3, val); break;
+	      case  4: STS( 4, val); break;
+	      case  5: STS( 5, val); break;
+	      case  6: STS( 6, val); break;
+	      case  7: STS( 7, val); break;
+	      case  8: STS( 8, val); break;
+	      case  9: STS( 9, val); break;
+	      case 10: STS(10, val); break;
+	      case 11: STS(11, val); break;
+	      case 12: STS(12, val); break;
+	      case 13: STS(13, val); break;
+	      case 14: STS(14, val); break;
+	      case 15: STS(15, val); break;
+	      case 16: STS(16, val); break;
+	      case 17: STS(17, val); break;
+	      case 18: STS(18, val); break;
+	      case 19: STS(19, val); break;
+	      case 20: STS(20, val); break;
+	      case 21: STS(21, val); break;
+	      case 22: STS(22, val); break;
+	      case 23: STS(23, val); break;
+	      case 24: STS(24, val); break;
+	      case 25: STS(25, val); break;
+	      case 26: STS(26, val); break;
+	      case 27: STS(27, val); break;
+	      case 28: STS(28, val); break;
+	      case 29: STS(29, val); break;
+	      case 30: STS(30, val); break;
+	      case 31: STS(31, val); break;
+	}
+	preempt_enable();
+	return val;
+}
+EXPORT_SYMBOL(alpha_read_fp_reg_s);
+
+#if defined(CONFIG_ALPHA_EV6) || defined(CONFIG_ALPHA_EV67)
+#define LDS(reg,val)  asm volatile ("itofs %0,$f"#reg : : "r"(val));
+#else
+#define LDS(reg,val)  asm volatile ("lds $f"#reg",%0" : : "m"(val));
+#endif
+
+void
+alpha_write_fp_reg_s (unsigned long reg, unsigned long val)
+{
+	if (unlikely(reg >= 32))
+		return;
+
+	preempt_disable();
+	if (current_thread_info()->status & TS_SAVED_FP) {
+		current_thread_info()->status |= TS_RESTORE_FP;
+		LDS(0, val);
+		STT(0, current_thread_info()->fp[reg]);
+	} else switch (reg) {
+	      case  0: LDS( 0, val); break;
+	      case  1: LDS( 1, val); break;
+	      case  2: LDS( 2, val); break;
+	      case  3: LDS( 3, val); break;
+	      case  4: LDS( 4, val); break;
+	      case  5: LDS( 5, val); break;
+	      case  6: LDS( 6, val); break;
+	      case  7: LDS( 7, val); break;
+	      case  8: LDS( 8, val); break;
+	      case  9: LDS( 9, val); break;
+	      case 10: LDS(10, val); break;
+	      case 11: LDS(11, val); break;
+	      case 12: LDS(12, val); break;
+	      case 13: LDS(13, val); break;
+	      case 14: LDS(14, val); break;
+	      case 15: LDS(15, val); break;
+	      case 16: LDS(16, val); break;
+	      case 17: LDS(17, val); break;
+	      case 18: LDS(18, val); break;
+	      case 19: LDS(19, val); break;
+	      case 20: LDS(20, val); break;
+	      case 21: LDS(21, val); break;
+	      case 22: LDS(22, val); break;
+	      case 23: LDS(23, val); break;
+	      case 24: LDS(24, val); break;
+	      case 25: LDS(25, val); break;
+	      case 26: LDS(26, val); break;
+	      case 27: LDS(27, val); break;
+	      case 28: LDS(28, val); break;
+	      case 29: LDS(29, val); break;
+	      case 30: LDS(30, val); break;
+	      case 31: LDS(31, val); break;
+	}
+	preempt_enable();
+}
+EXPORT_SYMBOL(alpha_write_fp_reg_s);