[PATCH v3 02/22] x86,mce: Delete ist_begin_non_atomic()

Peter Zijlstra
2020-02-19T15:15:02Z

It is an abomination; and in prepration of removing the whole
ist_enter() thing, it needs to go.

Convert #MC over to using task_work_add() instead; it will run the
same code slightly later, on the return to user path of the same
exception.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
---
arch/x86/include/asm/traps.h | 2 -
arch/x86/kernel/cpu/mce/core.c | 53 +++++++++++++++++++++++------------------
arch/x86/kernel/traps.c | 37 ----------------------------
include/linux/sched.h | 6 ++++
4 files changed, 36 insertions(+), 62 deletions(-)

--- a/arch/x86/include/asm/traps.h
+++ b/arch/x86/include/asm/traps.h
@@ -123,8 +123,6 @@ asmlinkage void smp_irq_move_cleanup_int

extern void ist_enter(struct pt_regs *regs);
extern void ist_exit(struct pt_regs *regs);
-extern void ist_begin_non_atomic(struct pt_regs *regs);
-extern void ist_end_non_atomic(void);

#ifdef CONFIG_VMAP_STACK
void __noreturn handle_stack_overflow(const char *message,
--- a/arch/x86/kernel/cpu/mce/core.c
+++ b/arch/x86/kernel/cpu/mce/core.c
@@ -42,6 +42,7 @@
#include <linux/export.h>
#include <linux/jump_label.h>
#include <linux/set_memory.h>
+#include <linux/task_work.h>

#include <asm/intel-family.h>
#include <asm/processor.h>
@@ -1084,23 +1085,6 @@ static void mce_clear_state(unsigned lon
}
}

-static int do_memory_failure(struct mce *m)
-{
- int flags = MF_ACTION_REQUIRED;
- int ret;
-
- pr_err("Uncorrected hardware memory error in user-access at %llx", m->addr);
- if (!(m->mcgstatus & MCG_STATUS_RIPV))
- flags |= MF_MUST_KILL;
- ret = memory_failure(m->addr >> PAGE_SHIFT, flags);
- if (ret)
- pr_err("Memory error not recovered");
- else
- set_mce_nospec(m->addr >> PAGE_SHIFT);
- return ret;
-}
-
-
/*
* Cases where we avoid rendezvous handler timeout:
* 1) If this CPU is offline.
@@ -1202,6 +1186,29 @@ static void __mc_scan_banks(struct mce *
*m = *final;
}

+static void mce_kill_me_now(struct callback_head *ch)
+{
+ force_sig(SIGBUS);
+}
+
+static void mce_kill_me_maybe(struct callback_head *cb)
+{
+ struct task_struct *p = container_of(cb, struct task_struct, mce_kill_me);
+ int flags = MF_ACTION_REQUIRED;
+
+ pr_err("Uncorrected hardware memory error in user-access at %llx", p->mce_addr);
+ if (!(p->mce_status & MCG_STATUS_RIPV))
+ flags |= MF_MUST_KILL;
+
+ if (!memory_failure(p->mce_addr >> PAGE_SHIFT, flags)) {
+ set_mce_nospec(p->mce_addr >> PAGE_SHIFT);
+ return;
+ }
+
+ pr_err("Memory error not recovered");
+ mce_kill_me_now(cb);
+}
+
/*
* The actual machine check handler. This only handles real
* exceptions when something got corrupted coming in through int 18.
@@ -1344,13 +1351,13 @@ void do_machine_check(struct pt_regs *re

/* Fault was in user mode and we need to take some action */
if ((m.cs & 3) == 3) {
- ist_begin_non_atomic(regs);
- local_irq_enable();
+ current->mce_addr = m.addr;
+ current->mce_status = m.mcgstatus;
+ current->mce_kill_me.func = mce_kill_me_maybe;
+ if (kill_it)
+ current->mce_kill_me.func = mce_kill_me_now;

- if (kill_it || do_memory_failure(&m))
- force_sig(SIGBUS);
- local_irq_disable();
- ist_end_non_atomic();
+ task_work_add(current, &current->mce_kill_me, true);
} else {
if (!fixup_exception(regs, X86_TRAP_MC, error_code, 0))
mce_panic("Failed kernel mode recovery", &m, msg);
--- a/arch/x86/kernel/traps.c
+++ b/arch/x86/kernel/traps.c
@@ -117,43 +117,6 @@ void ist_exit(struct pt_regs *regs)
rcu_nmi_exit();
}

-/**
- * ist_begin_non_atomic() - begin a non-atomic section in an IST exception
- * @regs: regs passed to the IST exception handler
- *
- * IST exception handlers normally cannot schedule. As a special
- * exception, if the exception interrupted userspace code (i.e.
- * user_mode(regs) would return true) and the exception was not
- * a double fault, it can be safe to schedule. ist_begin_non_atomic()
- * begins a non-atomic section within an ist_enter()/ist_exit() region.
- * Callers are responsible for enabling interrupts themselves inside
- * the non-atomic section, and callers must call ist_end_non_atomic()
- * before ist_exit().
- */
-void ist_begin_non_atomic(struct pt_regs *regs)
-{
- BUG_ON(!user_mode(regs));
-
- /*
- * Sanity check: we need to be on the normal thread stack. This
- * will catch asm bugs and any attempt to use ist_preempt_enable
- * from double_fault.
- */
- BUG_ON(!on_thread_stack());
-
- preempt_enable_no_resched();
-}
-
-/**
- * ist_end_non_atomic() - begin a non-atomic section in an IST exception
- *
- * Ends a non-atomic section started with ist_begin_non_atomic().
- */
-void ist_end_non_atomic(void)
-{
- preempt_disable();
-}
-
int is_valid_bugaddr(unsigned long addr)
{
unsigned short ud;
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1285,6 +1285,12 @@ struct task_struct {
unsigned long prev_lowest_stack;
#endif

+#ifdef CONFIG_X86_MCE
+ u64 mce_addr;
+ u64 mce_status;
+ struct callback_head mce_kill_me;
+#endif
+
/*
* New fields for task_struct should be added above here, so that
* they are included in the randomized portion of task_struct.