x86/speculation: Add __update_spec_ctrl() helper

Add a new __update_spec_ctrl() helper which is a variant of
update_spec_ctrl() that can be used in a noinstr function.

Suggested-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Waiman Long <longman@redhat.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Acked-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: https://lore.kernel.org/r/20230727184600.26768-2-longman@redhat.com

diff --git a/arch/x86/include/asm/spec-ctrl.h b/arch/x86/include/asm/spec-ctrl.h
index cb0386fc4dc3b3a4e240213a32c5f210cf8ce60f..c648502e453579e3d0deeb9033f2832d9a2fd2a1 100644 (file)
--- a/arch/x86/include/asm/spec-ctrl.h
+++ b/arch/x86/include/asm/spec-ctrl.h
@@ -4,6 +4,7 @@
 
 #include <linux/thread_info.h>
 #include <asm/nospec-branch.h>
+#include <asm/msr.h>
 
 /*
  * On VMENTER we must preserve whatever view of the SPEC_CTRL MSR
@@ -76,6 +77,16 @@ static inline u64 ssbd_tif_to_amd_ls_cfg(u64 tifn)
        return (tifn & _TIF_SSBD) ? x86_amd_ls_cfg_ssbd_mask : 0ULL;
 }
 
+/*
+ * This can be used in noinstr functions & should only be called in bare
+ * metal context.
+ */
+static __always_inline void __update_spec_ctrl(u64 val)
+{
+       __this_cpu_write(x86_spec_ctrl_current, val);
+       native_wrmsrl(MSR_IA32_SPEC_CTRL, val);
+}
+
 #ifdef CONFIG_SMP
 extern void speculative_store_bypass_ht_init(void);
 #else