On Tue, Mar 17, 2015 at 08:21:18AM +0100, Ingo Molnar wrote:
> Assuming this does not fix the regression, could you apply the minimal
> patch below - which reverts the old_rsp handling change.
>
> (The rest of the commit are in a third patch, but those are only
> comment changes.)
>
> So my theory is that this change is what will revert the regression.
Yep, it does. Below is the diff that works (it is the rough revert
without the comments :-)):
---
diff --git a/arch/x86/include/asm/processor.h b/arch/x86/include/asm/processor.h
index 66a1954439ea..e39bf83cb55b 100644
--- a/arch/x86/include/asm/processor.h
+++ b/arch/x86/include/asm/processor.h
@@ -496,6 +496,7 @@ struct thread_struct {
#ifdef CONFIG_X86_32
unsigned long sysenter_cs;
#else
+ unsigned long usersp; /* Copy from PDA */
unsigned short es;
unsigned short ds;
unsigned short fsindex;
@@ -907,6 +908,11 @@ extern unsigned long thread_saved_pc(struct task_struct *tsk);
#define task_pt_regs(tsk) ((struct pt_regs *)(tsk)->thread.sp0 - 1)
extern unsigned long KSTK_ESP(struct task_struct *task);
+/*
+ * User space RSP while inside the SYSCALL fast path
+ */
+DECLARE_PER_CPU(unsigned long, old_rsp);
+
#endif /* CONFIG_X86_64 */
extern void start_thread(struct pt_regs *regs, unsigned long new_ip,
diff --git a/arch/x86/kernel/process_64.c b/arch/x86/kernel/process_64.c
index 14df2be4711f..e8c124a1f885 100644
--- a/arch/x86/kernel/process_64.c
+++ b/arch/x86/kernel/process_64.c
@@ -161,6 +161,7 @@ int copy_thread(unsigned long clone_flags, unsigned long sp,
p->thread.sp0 = (unsigned long)task_stack_page(p) + THREAD_SIZE;
childregs = task_pt_regs(p);
p->thread.sp = (unsigned long) childregs;
+ p->thread.usersp = me->thread.usersp;
set_tsk_thread_flag(p, TIF_FORK);
p->thread.io_bitmap_ptr = NULL;
@@ -234,8 +235,10 @@ start_thread_common(struct pt_regs *regs, unsigned long new_ip,
loadsegment(es, _ds);
loadsegment(ds, _ds);
load_gs_index(0);
+ current->thread.usersp = new_sp;
regs->ip = new_ip;
regs->sp = new_sp;
+ this_cpu_write(old_rsp, new_sp);
regs->cs = _cs;
regs->ss = _ss;
regs->flags = X86_EFLAGS_IF;
@@ -395,6 +398,8 @@ __switch_to(struct task_struct *prev_p, struct task_struct *next_p)
/*
* Switch the PDA and FPU contexts.
*/
+ prev->usersp = this_cpu_read(old_rsp);
+ this_cpu_write(old_rsp, next->usersp);
this_cpu_write(current_task, next_p);
/*
--
Regards/Gruss,
Boris.
ECO tip #101: Trim your mails when you reply.
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