[xen master] x86/msr: Split out tsc.h

[patchbot@xxxxxxx]

commit 2b3d1c8a30d0df73665c16470ee1365c6d73589c
Author:     Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
AuthorDate: Fri Aug 15 13:33:01 2025 +0100
Commit:     Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
CommitDate: Tue Aug 19 19:52:48 2025 +0100

    x86/msr: Split out tsc.h
    
    The TSC functionality is only related to MSRs by write_tsc(), and this 
really
    does not want to be available as widely as is currently is.
    
    asm/time.h shouldn't be including asm/msr.h, but this turns out to be
    sufficiently tangled that I've chosen to break it out into it's own patch.
    
    No functional change.
    
    Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
    Acked-by: Jan Beulich <jbeulich@xxxxxxxx>
---
 xen/arch/x86/include/asm/msr.h  | 39 --------------------------------
 xen/arch/x86/include/asm/time.h |  1 +
 xen/arch/x86/include/asm/tsc.h  | 49 +++++++++++++++++++++++++++++++++++++++++
 3 files changed, 50 insertions(+), 39 deletions(-)

diff --git a/xen/arch/x86/include/asm/msr.h b/xen/arch/x86/include/asm/msr.h
index 9d1cb4e6ee..39f0bdbe7f 100644
--- a/xen/arch/x86/include/asm/msr.h
+++ b/xen/arch/x86/include/asm/msr.h
@@ -98,45 +98,6 @@ static inline void msr_split(struct cpu_user_regs *regs, 
uint64_t val)
     regs->rax = (uint32_t)val;
 }
 
-static inline uint64_t rdtsc(void)
-{
-    uint64_t low, high;
-
-    __asm__ __volatile__("rdtsc" : "=a" (low), "=d" (high));
-
-    return (high << 32) | low;
-}
-
-static inline uint64_t rdtsc_ordered(void)
-{
-    uint64_t low, high, aux;
-
-    /*
-     * The RDTSC instruction is not serializing.  Make it dispatch serializing
-     * for the purposes here by issuing LFENCE (or MFENCE if necessary) ahead
-     * of it.
-     *
-     * RDTSCP, otoh, "does wait until all previous instructions have executed
-     * and all previous loads are globally visible" (SDM) / "forces all older
-     * instructions to retire before reading the timestamp counter" (APM).
-     */
-    alternative_io_2("lfence; rdtsc",
-                     "mfence; rdtsc", X86_FEATURE_MFENCE_RDTSC,
-                     "rdtscp",        X86_FEATURE_RDTSCP,
-                     ASM_OUTPUT2("=a" (low), "=d" (high), "=c" (aux)),
-                     /* no inputs */);
-
-    return (high << 32) | low;
-}
-
-#define __write_tsc(val) wrmsrl(MSR_IA32_TSC, val)
-#define write_tsc(val) ({                                       \
-    /* Reliable TSCs are in lockstep across all CPUs. We should \
-     * never write to them. */                                  \
-    ASSERT(!boot_cpu_has(X86_FEATURE_TSC_RELIABLE));            \
-    __write_tsc(val);                                           \
-})
-
 #define rdpmc(counter,low,high) \
      __asm__ __volatile__("rdpmc" \
                          : "=a" (low), "=d" (high) \
diff --git a/xen/arch/x86/include/asm/time.h b/xen/arch/x86/include/asm/time.h
index 3dfbb5297a..c55b698314 100644
--- a/xen/arch/x86/include/asm/time.h
+++ b/xen/arch/x86/include/asm/time.h
@@ -3,6 +3,7 @@
 #define __X86_TIME_H__
 
 #include <asm/msr.h>
+#include <asm/tsc.h>
 
 typedef u64 cycles_t;
 
diff --git a/xen/arch/x86/include/asm/tsc.h b/xen/arch/x86/include/asm/tsc.h
new file mode 100644
index 0000000000..12557a7ee0
--- /dev/null
+++ b/xen/arch/x86/include/asm/tsc.h
@@ -0,0 +1,49 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+#ifndef X86_TSC_H
+#define X86_TSC_H
+
+#include <asm/alternative.h>
+
+static inline uint64_t rdtsc(void)
+{
+    uint64_t low, high;
+
+    asm volatile ( "rdtsc" : "=a" (low), "=d" (high) );
+
+    return (high << 32) | low;
+}
+
+static inline uint64_t rdtsc_ordered(void)
+{
+    uint64_t low, high, aux;
+
+    /*
+     * The RDTSC instruction is not serializing.  Make it dispatch serializing
+     * for the purposes here by issuing LFENCE (or MFENCE if necessary) ahead
+     * of it.
+     *
+     * RDTSCP, otoh, "does wait until all previous instructions have executed
+     * and all previous loads are globally visible" (SDM) / "forces all older
+     * instructions to retire before reading the timestamp counter" (APM).
+     */
+    alternative_io_2("lfence; rdtsc",
+                     "mfence; rdtsc", X86_FEATURE_MFENCE_RDTSC,
+                     "rdtscp",        X86_FEATURE_RDTSCP,
+                     ASM_OUTPUT2("=a" (low), "=d" (high), "=c" (aux)),
+                     /* no inputs */);
+
+    return (high << 32) | low;
+}
+
+#define __write_tsc(val) wrmsrl(MSR_IA32_TSC, val)
+
+/*
+ * Reliable TSCs are in lockstep across all CPUs. We should never write to
+ * them.
+ */
+#define write_tsc(val) ({                                       \
+    ASSERT(!boot_cpu_has(X86_FEATURE_TSC_RELIABLE));            \
+    __write_tsc(val);                                           \
+})
+
+#endif /* X86_TSC_H */
--
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