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Date: Mon, 23 Sep 2019 14:10:01 +0200
From: Peter Zijlstra <peterz@...radead.org>
To: Thomas Gleixner <tglx@...utronix.de>
Cc: LKML <linux-kernel@...r.kernel.org>, x86@...nel.org,
Andy Lutomirski <luto@...nel.org>,
Catalin Marinas <catalin.marinas@....com>,
Will Deacon <will@...nel.org>,
Mark Rutland <mark.rutland@....com>,
Marc Zyngier <maz@...nel.org>,
Paolo Bonzini <pbonzini@...hat.com>, kvm@...r.kernel.org,
linux-arch@...r.kernel.org, jgross@...e.com
Subject: Re: [RFC patch 10/15] x86/entry: Move irq tracing to C code
On Mon, Sep 23, 2019 at 01:55:51PM +0200, Peter Zijlstra wrote:
> On Mon, Sep 23, 2019 at 01:49:20PM +0200, Peter Zijlstra wrote:
> > While walking the kids to school I wondered WTH we need to call
> > TRACE_IRQS_OFF in the first place. If this is the return from exception
> > path, interrupts had better be disabled already (in exception enter).
> >
> > For entry_64.S we have:
> >
> > - idtentry_part; which does TRACE_IRQS_OFF at the start and error_exit
> > at the end.
> >
> > - xen_do_hypervisor_callback, xen_failsafe_callback -- which are
> > confusing.
> >
> > So in the normal case, it appears we can simply do:
> >
> > diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S
> > index b7c3ea4cb19d..e9cf59ac554e 100644
> > --- a/arch/x86/entry/entry_64.S
> > +++ b/arch/x86/entry/entry_64.S
> > @@ -1368,8 +1368,6 @@ END(error_entry)
> >
> > ENTRY(error_exit)
> > UNWIND_HINT_REGS
> > - DISABLE_INTERRUPTS(CLBR_ANY)
> > - TRACE_IRQS_OFF
> > testb $3, CS(%rsp)
> > jz retint_kernel
> > jmp retint_user
> >
> > and all should be well. This leaves Xen...
> >
> > For entry_32.S it looks like nothing uses 'resume_userspace' so that
> > ENTRY can go away. Which then leaves:
> >
> > * ret_from_intr:
> > - common_spurious: TRACE_IRQS_OFF
> > - common_interrupt: TRACE_IRQS_OFF
> > - BUILD_INTERRUPT3: TRACE_IRQS_OFF
> > - xen_do_upcall: ...
> >
> > * ret_from_exception:
> > - xen_failsafe_callback: ...
> > - common_exception_read_cr2: TRACE_IRQS_OFF
> > - common_exception: TRACE_IRQS_OFF
> > - int3: TRACE_IRQS_OFF
> >
> > Which again suggests:
> >
> > diff --git a/arch/x86/entry/entry_32.S b/arch/x86/entry/entry_32.S
> > index f83ca5aa8b77..7a19e7413a8e 100644
> > --- a/arch/x86/entry/entry_32.S
> > +++ b/arch/x86/entry/entry_32.S
> > @@ -825,9 +825,6 @@ END(ret_from_fork)
> > cmpl $USER_RPL, %eax
> > jb restore_all_kernel # not returning to v8086 or userspace
> >
> > -ENTRY(resume_userspace)
> > - DISABLE_INTERRUPTS(CLBR_ANY)
> > - TRACE_IRQS_OFF
> > movl %esp, %eax
> > call prepare_exit_to_usermode
> > jmp restore_all
> >
> > with the notable exception (oh teh pun!) being Xen... _again_.
> >
> > With these patchlets on, we'd want prepare_exit_to_usermode() to
> > validate the IRQ state, but AFAICT it _should_ all just 'work' (famous
> > last words).
> >
> > Cc Juergen because Xen
>
> Arrgh.. faults!! they do local_irq_enable() but never disable them
> again. Arguably those functions should be symmetric and restore IF when
> they muck with it instead of relying on the exit path fixing things up.
---
diff --git a/arch/x86/entry/entry_32.S b/arch/x86/entry/entry_32.S
index f83ca5aa8b77..7a19e7413a8e 100644
--- a/arch/x86/entry/entry_32.S
+++ b/arch/x86/entry/entry_32.S
@@ -825,9 +825,6 @@ END(ret_from_fork)
cmpl $USER_RPL, %eax
jb restore_all_kernel # not returning to v8086 or userspace
-ENTRY(resume_userspace)
- DISABLE_INTERRUPTS(CLBR_ANY)
- TRACE_IRQS_OFF
movl %esp, %eax
call prepare_exit_to_usermode
jmp restore_all
diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S
index b7c3ea4cb19d..e9cf59ac554e 100644
--- a/arch/x86/entry/entry_64.S
+++ b/arch/x86/entry/entry_64.S
@@ -1368,8 +1368,6 @@ END(error_entry)
ENTRY(error_exit)
UNWIND_HINT_REGS
- DISABLE_INTERRUPTS(CLBR_ANY)
- TRACE_IRQS_OFF
testb $3, CS(%rsp)
jz retint_kernel
jmp retint_user
diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c
index 4bb0f8447112..663d44c68f67 100644
--- a/arch/x86/kernel/traps.c
+++ b/arch/x86/kernel/traps.c
@@ -276,6 +276,7 @@ static void do_error_trap(struct pt_regs *regs, long error_code, char *str,
NOTIFY_STOP) {
cond_local_irq_enable(regs);
do_trap(trapnr, signr, str, regs, error_code, sicode, addr);
+ cond_local_irq_disable(regs);
}
}
@@ -501,6 +502,7 @@ dotraplinkage void do_bounds(struct pt_regs *regs, long error_code)
die("bounds", regs, error_code);
}
+ cond_local_irq_disable(regs);
return;
exit_trap:
@@ -512,6 +514,7 @@ dotraplinkage void do_bounds(struct pt_regs *regs, long error_code)
* time..
*/
do_trap(X86_TRAP_BR, SIGSEGV, "bounds", regs, error_code, 0, NULL);
+ cond_local_irq_disable(regs);
}
dotraplinkage void
@@ -525,19 +528,19 @@ do_general_protection(struct pt_regs *regs, long error_code)
if (static_cpu_has(X86_FEATURE_UMIP)) {
if (user_mode(regs) && fixup_umip_exception(regs))
- return;
+ goto exit_trap;
}
if (v8086_mode(regs)) {
local_irq_enable();
handle_vm86_fault((struct kernel_vm86_regs *) regs, error_code);
- return;
+ goto exit_trap;
}
tsk = current;
if (!user_mode(regs)) {
if (fixup_exception(regs, X86_TRAP_GP, error_code, 0))
- return;
+ goto exit_trap;
tsk->thread.error_code = error_code;
tsk->thread.trap_nr = X86_TRAP_GP;
@@ -549,12 +552,12 @@ do_general_protection(struct pt_regs *regs, long error_code)
*/
if (!preemptible() && kprobe_running() &&
kprobe_fault_handler(regs, X86_TRAP_GP))
- return;
+ goto exit_trap;
if (notify_die(DIE_GPF, desc, regs, error_code,
X86_TRAP_GP, SIGSEGV) != NOTIFY_STOP)
die(desc, regs, error_code);
- return;
+ goto exit_trap;
}
tsk->thread.error_code = error_code;
@@ -563,6 +566,8 @@ do_general_protection(struct pt_regs *regs, long error_code)
show_signal(tsk, SIGSEGV, "", desc, regs, error_code);
force_sig(SIGSEGV);
+exit_trap:
+ cond_local_irq_disable(regs);
}
NOKPROBE_SYMBOL(do_general_protection);
@@ -783,9 +788,7 @@ dotraplinkage void do_debug(struct pt_regs *regs, long error_code)
if (v8086_mode(regs)) {
handle_vm86_trap((struct kernel_vm86_regs *) regs, error_code,
X86_TRAP_DB);
- cond_local_irq_disable(regs);
- debug_stack_usage_dec();
- goto exit;
+ goto exit_irq;
}
if (WARN_ON_ONCE((dr6 & DR_STEP) && !user_mode(regs))) {
@@ -802,6 +805,8 @@ dotraplinkage void do_debug(struct pt_regs *regs, long error_code)
si_code = get_si_code(tsk->thread.debugreg6);
if (tsk->thread.debugreg6 & (DR_STEP | DR_TRAP_BITS) || user_icebp)
send_sigtrap(regs, error_code, si_code);
+
+exit_irq:
cond_local_irq_disable(regs);
debug_stack_usage_dec();
@@ -827,7 +832,7 @@ static void math_error(struct pt_regs *regs, int error_code, int trapnr)
if (!user_mode(regs)) {
if (fixup_exception(regs, trapnr, error_code, 0))
- return;
+ goto exit_trap;
task->thread.error_code = error_code;
task->thread.trap_nr = trapnr;
@@ -835,7 +840,7 @@ static void math_error(struct pt_regs *regs, int error_code, int trapnr)
if (notify_die(DIE_TRAP, str, regs, error_code,
trapnr, SIGFPE) != NOTIFY_STOP)
die(str, regs, error_code);
- return;
+ goto exit_trap;
}
/*
@@ -849,10 +854,12 @@ static void math_error(struct pt_regs *regs, int error_code, int trapnr)
si_code = fpu__exception_code(fpu, trapnr);
/* Retry when we get spurious exceptions: */
if (!si_code)
- return;
+ goto exit_trap;
force_sig_fault(SIGFPE, si_code,
(void __user *)uprobe_get_trap_addr(regs));
+exit_trap:
+ cond_local_irq_disable(regs);
}
dotraplinkage void do_coprocessor_error(struct pt_regs *regs, long error_code)
@@ -889,6 +896,8 @@ do_device_not_available(struct pt_regs *regs, long error_code)
info.regs = regs;
math_emulate(&info);
+
+ cond_local_irq_disable(regs);
return;
}
#endif
diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c
index 9ceacd1156db..501cc36a3d6a 100644
--- a/arch/x86/mm/fault.c
+++ b/arch/x86/mm/fault.c
@@ -1500,10 +1500,13 @@ __do_page_fault(struct pt_regs *regs, unsigned long hw_error_code,
return;
/* Was the fault on kernel-controlled part of the address space? */
- if (unlikely(fault_in_kernel_space(address)))
+ if (unlikely(fault_in_kernel_space(address))) {
do_kern_addr_fault(regs, hw_error_code, address);
- else
+ } else {
do_user_addr_fault(regs, hw_error_code, address);
+ if (regs->flags & X86_EFLAGS_IF)
+ local_irq_disable();
+ }
}
NOKPROBE_SYMBOL(__do_page_fault);
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