[tip: x86/build] x86/entry: Remove unwanted instrumentation in common_interrupt()

[tip-bot2 for Dmitry Vyukov]

The following commit has been merged into the x86/build branch of tip:

Commit-ID:     477d81a1c47a1b79b9c08fc92b5dea3c5143800b
Gitweb:        https://git.kernel.org/tip/477d81a1c47a1b79b9c08fc92b5dea3c5143800b
Author:        Dmitry Vyukov <dvyukov@xxxxxxxxxx>
AuthorDate:    Tue, 11 Jun 2024 09:50:30 +02:00
Committer:     Thomas Gleixner <tglx@xxxxxxxxxxxxx>
CommitterDate: Thu, 08 Aug 2024 17:36:35 +02:00

x86/entry: Remove unwanted instrumentation in common_interrupt()

common_interrupt() and related variants call kvm_set_cpu_l1tf_flush_l1d(),
which is neither marked noinstr nor __always_inline.

So compiler puts it out of line and adds instrumentation to it.  Since the
call is inside of instrumentation_begin/end(), objtool does not warn about
it.

The manifestation is that KCOV produces spurious coverage in
kvm_set_cpu_l1tf_flush_l1d() in random places because the call happens when
preempt count is not yet updated to say that the kernel is in an interrupt.

Mark kvm_set_cpu_l1tf_flush_l1d() as __always_inline and move it out of the
instrumentation_begin/end() section.  It only calls __this_cpu_write()
which is already safe to call in noinstr contexts.

Fixes: 6368558c3710 ("x86/entry: Provide IDTENTRY_SYSVEC")
Signed-off-by: Dmitry Vyukov <dvyukov@xxxxxxxxxx>
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Reviewed-by: Alexander Potapenko <glider@xxxxxxxxxx>
Acked-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx
Link: https://lore.kernel.org/all/3f9a1de9e415fcb53d07dc9e19fa8481bb021b1b.1718092070.git.dvyukov@xxxxxxxxxx

---
 arch/x86/include/asm/hardirq.h  | 8 ++++++--
 arch/x86/include/asm/idtentry.h | 6 +++---
 2 files changed, 9 insertions(+), 5 deletions(-)

diff --git a/arch/x86/include/asm/hardirq.h b/arch/x86/include/asm/hardirq.h
index c67fa6a..6ffa8b7 100644
--- a/arch/x86/include/asm/hardirq.h
+++ b/arch/x86/include/asm/hardirq.h
@@ -69,7 +69,11 @@ extern u64 arch_irq_stat(void);
 #define local_softirq_pending_ref       pcpu_hot.softirq_pending
 
 #if IS_ENABLED(CONFIG_KVM_INTEL)
-static inline void kvm_set_cpu_l1tf_flush_l1d(void)
+/*
+ * This function is called from noinstr interrupt contexts
+ * and must be inlined to not get instrumentation.
+ */
+static __always_inline void kvm_set_cpu_l1tf_flush_l1d(void)
 {
 	__this_cpu_write(irq_stat.kvm_cpu_l1tf_flush_l1d, 1);
 }
@@ -84,7 +88,7 @@ static __always_inline bool kvm_get_cpu_l1tf_flush_l1d(void)
 	return __this_cpu_read(irq_stat.kvm_cpu_l1tf_flush_l1d);
 }
 #else /* !IS_ENABLED(CONFIG_KVM_INTEL) */
-static inline void kvm_set_cpu_l1tf_flush_l1d(void) { }
+static __always_inline void kvm_set_cpu_l1tf_flush_l1d(void) { }
 #endif /* IS_ENABLED(CONFIG_KVM_INTEL) */
 
 #endif /* _ASM_X86_HARDIRQ_H */
diff --git a/arch/x86/include/asm/idtentry.h b/arch/x86/include/asm/idtentry.h
index d4f2449..ad5c68f 100644
--- a/arch/x86/include/asm/idtentry.h
+++ b/arch/x86/include/asm/idtentry.h
@@ -212,8 +212,8 @@ __visible noinstr void func(struct pt_regs *regs,			\
 	irqentry_state_t state = irqentry_enter(regs);			\
 	u32 vector = (u32)(u8)error_code;				\
 									\
+	kvm_set_cpu_l1tf_flush_l1d();                                   \
 	instrumentation_begin();					\
-	kvm_set_cpu_l1tf_flush_l1d();					\
 	run_irq_on_irqstack_cond(__##func, regs, vector);		\
 	instrumentation_end();						\
 	irqentry_exit(regs, state);					\
@@ -250,7 +250,6 @@ static void __##func(struct pt_regs *regs);				\
 									\
 static __always_inline void instr_##func(struct pt_regs *regs)		\
 {									\
-	kvm_set_cpu_l1tf_flush_l1d();					\
 	run_sysvec_on_irqstack_cond(__##func, regs);			\
 }									\
 									\
@@ -258,6 +257,7 @@ __visible noinstr void func(struct pt_regs *regs)			\
 {									\
 	irqentry_state_t state = irqentry_enter(regs);			\
 									\
+	kvm_set_cpu_l1tf_flush_l1d();                                   \
 	instrumentation_begin();					\
 	instr_##func (regs);						\
 	instrumentation_end();						\
@@ -288,7 +288,6 @@ static __always_inline void __##func(struct pt_regs *regs);		\
 static __always_inline void instr_##func(struct pt_regs *regs)		\
 {									\
 	__irq_enter_raw();						\
-	kvm_set_cpu_l1tf_flush_l1d();					\
 	__##func (regs);						\
 	__irq_exit_raw();						\
 }									\
@@ -297,6 +296,7 @@ __visible noinstr void func(struct pt_regs *regs)			\
 {									\
 	irqentry_state_t state = irqentry_enter(regs);			\
 									\
+	kvm_set_cpu_l1tf_flush_l1d();                                   \
 	instrumentation_begin();					\
 	instr_##func (regs);						\
 	instrumentation_end();						\