- Mark serialize() noinstr so that it can be used from instrumentation-free

code
 
 - Make sure FRED's RSP0 MSR is synchronized with its corresponding per-CPU
   value in order to avoid double faults in hotplug scenarios
 
 - Disable EXECMEM_ROX on x86 for now because it didn't receive proper x86
   maintainers review, went in and broke a bunch of things
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Merge tag 'x86_urgent_for_v6.13' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

Pull x86 fixes from Borislav Petkov:

 - Mark serialize() noinstr so that it can be used from instrumentation-
   free code

 - Make sure FRED's RSP0 MSR is synchronized with its corresponding
   per-CPU value in order to avoid double faults in hotplug scenarios

 - Disable EXECMEM_ROX on x86 for now because it didn't receive proper
   x86 maintainers review, went in and broke a bunch of things

* tag 'x86_urgent_for_v6.13' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  x86/asm: Make serialize() always_inline
  x86/fred: Fix the FRED RSP0 MSR out of sync with its per-CPU cache
  x86: Disable EXECMEM_ROX support

arch/x86/Kconfig

@@ -83,7 +83,6 @@ config X86
 	select ARCH_HAS_DMA_OPS			if GART_IOMMU || XEN
 	select ARCH_HAS_EARLY_DEBUG		if KGDB
 	select ARCH_HAS_ELF_RANDOMIZE
-	select ARCH_HAS_EXECMEM_ROX		if X86_64
 	select ARCH_HAS_FAST_MULTIPLIER
 	select ARCH_HAS_FORTIFY_SOURCE
 	select ARCH_HAS_GCOV_PROFILE_ALL

arch/x86/include/asm/special_insns.h

@@ -217,7 +217,7 @@ fail:
 
 #define nop() asm volatile ("nop")
 
-static inline void serialize(void)
+static __always_inline void serialize(void)
 {
 	/* Instruction opcode for SERIALIZE; supported in binutils >= 2.35. */
 	asm volatile(".byte 0xf, 0x1, 0xe8" ::: "memory");

arch/x86/kernel/fred.c

@@ -50,7 +50,13 @@ void cpu_init_fred_exceptions(void)
 	       FRED_CONFIG_ENTRYPOINT(asm_fred_entrypoint_user));
 
 	wrmsrl(MSR_IA32_FRED_STKLVLS, 0);
-	wrmsrl(MSR_IA32_FRED_RSP0, 0);
+
+	/*
+	 * Ater a CPU offline/online cycle, the FRED RSP0 MSR should be
+	 * resynchronized with its per-CPU cache.
+	 */
+	wrmsrl(MSR_IA32_FRED_RSP0, __this_cpu_read(fred_rsp0));
+
 	wrmsrl(MSR_IA32_FRED_RSP1, 0);
 	wrmsrl(MSR_IA32_FRED_RSP2, 0);
 	wrmsrl(MSR_IA32_FRED_RSP3, 0);