On 7/3/23 06:28, Peter Zijlstra wrote:
On Tue, Jun 27, 2023 at 10:25:51PM -0400, Waiman Long wrote:
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@xxxxxxxxxxxxx>
Signed-off-by: Waiman Long <longman@xxxxxxxxxx>
---
arch/x86/include/asm/nospec-branch.h | 11 ++++++++++-
1 file changed, 10 insertions(+), 1 deletion(-)
diff --git a/arch/x86/include/asm/nospec-branch.h b/arch/x86/include/asm/nospec-branch.h
index 55388c9f7601..1d363fcea207 100644
--- a/arch/x86/include/asm/nospec-branch.h
+++ b/arch/x86/include/asm/nospec-branch.h
@@ -9,7 +9,7 @@
#include <asm/alternative.h>
#include <asm/cpufeatures.h>
-#include <asm/msr-index.h>
+#include <asm/msr.h>
#include <asm/unwind_hints.h>
#include <asm/percpu.h>
#include <asm/current.h>
@@ -488,6 +488,15 @@ DECLARE_PER_CPU(u64, x86_spec_ctrl_current);
extern void update_spec_ctrl_cond(u64 val);
extern u64 spec_ctrl_current(void);
+/*
+ * This can be used in noinstr function.
+ */
+static __always_inline void __update_spec_ctrl(u64 val)
+{
+ __this_cpu_write(x86_spec_ctrl_current, val);
+ native_wrmsrl(MSR_IA32_SPEC_CTRL, val);
+}
Should we also use this to implement update_spec_ctrl() ?
I also thought about that. However, I am a bit worry about losing some
additional check done in this_cpu_write() and the paravirt support in
wrmsrl(). I have no problem making update_spec_ctrl() an instrument-able
wrapper on __update_spec_ctrl() if you think these are not valid concerns.
Cheers,
Longman
