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Using a trampoline stack would obnoxious for Xen PV because Xen PV
enters entry_SYSCALL_64_after_hwframe on the stack indicated by sp0.
This could be fixed, but I think it's nice to ensure the entry code
can still work without a trampoline stack. So this patch doesn't
use the entry trampoline stack on Xen.
The regs != eregs check in sync_regs is optional, but I think it's
better than copying the whole set of regs over itself.
Signed-off-by: Andy Lutomirski <l...@kernel.org>
---
Boris, this is lightly tested and should fix the problem you're seeing.
arch/x86/include/asm/switch_to.h | 3 +++
arch/x86/kernel/traps.c | 9 +++++----
2 files changed, 8 insertions(+), 4 deletions(-)
diff --git a/arch/x86/include/asm/switch_to.h b/arch/x86/include/asm/switch_to.h
index fab453ad2460..cbc71e73bd32 100644
--- a/arch/x86/include/asm/switch_to.h
+++ b/arch/x86/include/asm/switch_to.h
@@ -93,6 +93,9 @@ static inline void update_sp0(struct task_struct *task)
/* On x86_64, sp0 always points to the entry trampoline stack, which is
constant: */
#ifdef CONFIG_X86_32
load_sp0(task->thread.sp0);
+#else
+ if (static_cpu_has(X86_FEATURE_XENPV))
+ load_sp0(task_top_of_stack(task));
#endif
}
diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c
index 40cc3dc5967a..ee9ca0ad4388 100644
--- a/arch/x86/kernel/traps.c
+++ b/arch/x86/kernel/traps.c
@@ -619,14 +619,15 @@ NOKPROBE_SYMBOL(do_int3);
#ifdef CONFIG_X86_64
/*
- * Help handler running on IST stack to switch off the IST stack if the
- * interrupted code was in user mode. The actual stack switch is done in
- * entry_64.S
+ * Help handler running on a per-cpu (IST or entry trampoline) stack
+ * to switch to the normal thread stack if the interrupted code was in
+ * user mode. The actual stack switch is done in entry_64.S
*/
asmlinkage __visible notrace struct pt_regs *sync_regs(struct pt_regs *eregs)
{
struct pt_regs *regs = (struct pt_regs
*)this_cpu_read(cpu_current_top_of_stack) - 1;
- *regs = *eregs;
+ if (regs != eregs)
+ *regs = *eregs;
return regs;
}
NOKPROBE_SYMBOL(sync_regs);
--
2.13.6
