5 files changed, 37 insertions, 22 deletions

diff --git a/arch/x86/include/asm/switch_to.h b/arch/x86/include/asm/switch_to.h
index 36bd243843d6..7cf1a270d891 100644
--- a/arch/x86/include/asm/switch_to.h
+++ b/arch/x86/include/asm/switch_to.h
@@ -11,9 +11,6 @@ struct task_struct *__switch_to_asm(struct task_struct *prev,
 
 __visible struct task_struct *__switch_to(struct task_struct *prev,
                                           struct task_struct *next);
-struct tss_struct;
-void __switch_to_xtra(struct task_struct *prev_p, struct task_struct *next_p,
-                      struct tss_struct *tss);
 
 /* This runs runs on the previous thread's stack. */
 static inline void prepare_switch_to(struct task_struct *next)
diff --git a/arch/x86/kernel/process.c b/arch/x86/kernel/process.c
index 574b144d2b53..cdf8e6694f71 100644
--- a/arch/x86/kernel/process.c
+++ b/arch/x86/kernel/process.c
@@ -40,6 +40,8 @@
 #include <asm/prctl.h>
 #include <asm/spec-ctrl.h>
 
+#include "process.h"
+
 /*
  * per-CPU TSS segments. Threads are completely 'soft' on Linux,
  * no more per-task TSS's. The TSS size is kept cacheline-aligned
@@ -252,11 +254,12 @@ void arch_setup_new_exec(void)
                 enable_cpuid();
 }
 
-static inline void switch_to_bitmap(struct tss_struct *tss,
-                                    struct thread_struct *prev,
+static inline void switch_to_bitmap(struct thread_struct *prev,
                                     struct thread_struct *next,
                                     unsigned long tifp, unsigned long tifn)
 {
+        struct tss_struct *tss = this_cpu_ptr(&cpu_tss_rw);
+
         if (tifn & _TIF_IO_BITMAP) {
                 /*
                  * Copy the relevant range of the IO bitmap.
@@ -448,8 +451,7 @@ void speculation_ctrl_update(unsigned long tif)
         preempt_enable();
 }
 
-void __switch_to_xtra(struct task_struct *prev_p, struct task_struct *next_p,
-                      struct tss_struct *tss)
+void __switch_to_xtra(struct task_struct *prev_p, struct task_struct *next_p)
 {
         struct thread_struct *prev, *next;
         unsigned long tifp, tifn;
@@ -459,7 +461,7 @@ void __switch_to_xtra(struct task_struct *prev_p, struct task_struct *next_p,
 
         tifn = READ_ONCE(task_thread_info(next_p)->flags);
         tifp = READ_ONCE(task_thread_info(prev_p)->flags);
-        switch_to_bitmap(tss, prev, next, tifp, tifn);
+        switch_to_bitmap(prev, next, tifp, tifn);
 
         propagate_user_return_notify(prev_p, next_p);
 
diff --git a/arch/x86/kernel/process.h b/arch/x86/kernel/process.h
new file mode 100644
index 000000000000..020fbfac3a27
--- /dev/null
+++ b/arch/x86/kernel/process.h
@@ -0,0 +1,24 @@
+// SPDX-License-Identifier: GPL-2.0
+//
+// Code shared between 32 and 64 bit
+
+void __switch_to_xtra(struct task_struct *prev_p, struct task_struct *next_p);
+
+/*
+ * This needs to be inline to optimize for the common case where no extra
+ * work needs to be done.
+ */
+static inline void switch_to_extra(struct task_struct *prev,
+                                   struct task_struct *next)
+{
+        unsigned long next_tif = task_thread_info(next)->flags;
+        unsigned long prev_tif = task_thread_info(prev)->flags;
+
+        /*
+         * __switch_to_xtra() handles debug registers, i/o bitmaps,
+         * speculation mitigations etc.
+         */
+        if (unlikely(next_tif & _TIF_WORK_CTXSW_NEXT ||
+                     prev_tif & _TIF_WORK_CTXSW_PREV))
+                __switch_to_xtra(prev, next);
+}
diff --git a/arch/x86/kernel/process_32.c b/arch/x86/kernel/process_32.c
index 5046a3c9dec2..d3e593eb189f 100644
--- a/arch/x86/kernel/process_32.c
+++ b/arch/x86/kernel/process_32.c
@@ -59,6 +59,8 @@
 #include <asm/intel_rdt_sched.h>
 #include <asm/proto.h>
 
+#include "process.h"
+
 void __show_regs(struct pt_regs *regs, enum show_regs_mode mode)
 {
         unsigned long cr0 = 0L, cr2 = 0L, cr3 = 0L, cr4 = 0L;
@@ -232,7 +234,6 @@ __switch_to(struct task_struct *prev_p, struct task_struct *next_p)
         struct fpu *prev_fpu = &prev->fpu;
         struct fpu *next_fpu = &next->fpu;
         int cpu = smp_processor_id();
-        struct tss_struct *tss = &per_cpu(cpu_tss_rw, cpu);
 
         /* never put a printk in __switch_to... printk() calls wake_up*() indirectly */
 
@@ -264,12 +265,7 @@ __switch_to(struct task_struct *prev_p, struct task_struct *next_p)
         if (get_kernel_rpl() && unlikely(prev->iopl != next->iopl))
                 set_iopl_mask(next->iopl);
 
-        /*
-         * Now maybe handle debug registers and/or IO bitmaps
-         */
-        if (unlikely(task_thread_info(prev_p)->flags & _TIF_WORK_CTXSW_PREV ||
-                     task_thread_info(next_p)->flags & _TIF_WORK_CTXSW_NEXT))
-                __switch_to_xtra(prev_p, next_p, tss);
+        switch_to_extra(prev_p, next_p);
 
         /*
          * Leave lazy mode, flushing any hypercalls made here.
diff --git a/arch/x86/kernel/process_64.c b/arch/x86/kernel/process_64.c
index 0e0b4288a4b2..bbfbf017065c 100644
--- a/arch/x86/kernel/process_64.c
+++ b/arch/x86/kernel/process_64.c
@@ -60,6 +60,8 @@
 #include <asm/unistd_32_ia32.h>
 #endif
 
+#include "process.h"
+
 /* Prints also some state that isn't saved in the pt_regs */
 void __show_regs(struct pt_regs *regs, enum show_regs_mode mode)
 {
@@ -553,7 +555,6 @@ __switch_to(struct task_struct *prev_p, struct task_struct *next_p)
         struct fpu *prev_fpu = &prev->fpu;
         struct fpu *next_fpu = &next->fpu;
         int cpu = smp_processor_id();
-        struct tss_struct *tss = &per_cpu(cpu_tss_rw, cpu);
 
         WARN_ON_ONCE(IS_ENABLED(CONFIG_DEBUG_ENTRY) &&
                      this_cpu_read(irq_count) != -1);
@@ -617,12 +618,7 @@ __switch_to(struct task_struct *prev_p, struct task_struct *next_p)
         /* Reload sp0. */
         update_task_stack(next_p);
 
-        /*
-         * Now maybe reload the debug registers and handle I/O bitmaps
-         */
-        if (unlikely(task_thread_info(next_p)->flags & _TIF_WORK_CTXSW_NEXT ||
-                     task_thread_info(prev_p)->flags & _TIF_WORK_CTXSW_PREV))
-                __switch_to_xtra(prev_p, next_p, tss);
+        switch_to_extra(prev_p, next_p);
 
 #ifdef CONFIG_XEN_PV
         /*