[PATCH v6 1/4] x86/speculation: Add __update_spec_ctrl() helper

Waiman Long
2023-07-27T18:47:11Z

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>
Acked-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
---
arch/x86/include/asm/spec-ctrl.h | 11 +++++++++++
1 file changed, 11 insertions(+)

diff --git a/arch/x86/include/asm/spec-ctrl.h b/arch/x86/include/asm/spec-ctrl.h
index cb0386fc4dc3..d03408e0468a 100644
--- 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 function & 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
--
2.31.1