[PATCH V8 23/44] entry: Add architecture auxiliary pt_regs save/restore calls

ira.weiny
2022-01-27T17:56:17Z

From: Ira Weiny <ira.weiny@intel.com>

Some architectures have auxiliary pt_regs space which is available to
store extra information on the stack. For ease of implementation the
common C code was left to fill in the data when needed.

Define C calls for architectures to save and restore any auxiliary data
they may need and call those from the common entry code.

NOTE: Due to the split nature of the Xen exit code
irqentry_exit_cond_resched() requires an unbalanced call to
arch_restore_aux_pt_regs() regardless of the nature of the preemption
configuration.

Signed-off-by: Ira Weiny <ira.weiny@intel.com>

---
Changes for V8
New patch which introduces a generic auxiliary pt_register save
restore.
---
include/linux/entry-common.h | 7 +++++++
kernel/entry/common.c | 16 ++++++++++++++--
2 files changed, 21 insertions(+), 2 deletions(-)

diff --git a/include/linux/entry-common.h b/include/linux/entry-common.h
index 14fd329847e7..b243f1cfd491 100644
--- a/include/linux/entry-common.h
+++ b/include/linux/entry-common.h
@@ -99,6 +99,13 @@ static inline __must_check int arch_syscall_enter_tracehook(struct pt_regs *regs
}
#endif

+#ifndef CONFIG_ARCH_HAS_PTREGS_AUXILIARY
+
+static inline void arch_save_aux_pt_regs(struct pt_regs *regs) { }
+static inline void arch_restore_aux_pt_regs(struct pt_regs *regs) { }
+
+#endif
+
/**
* enter_from_user_mode - Establish state when coming from user mode
*
diff --git a/kernel/entry/common.c b/kernel/entry/common.c
index f4210a7fc84d..c778e9783361 100644
--- a/kernel/entry/common.c
+++ b/kernel/entry/common.c
@@ -323,7 +323,7 @@ noinstr irqentry_state_t irqentry_enter(struct pt_regs *regs)

if (user_mode(regs)) {
irqentry_enter_from_user_mode(regs);
- return ret;
+ goto aux_save;
}

/*
@@ -362,7 +362,7 @@ noinstr irqentry_state_t irqentry_enter(struct pt_regs *regs)
instrumentation_end();

ret.exit_rcu = true;
- return ret;
+ goto aux_save;
}

/*
@@ -377,6 +377,11 @@ noinstr irqentry_state_t irqentry_enter(struct pt_regs *regs)
trace_hardirqs_off_finish();
instrumentation_end();

+aux_save:
+ instrumentation_begin();
+ arch_save_aux_pt_regs(regs);
+ instrumentation_end();
+
return ret;
}

@@ -408,6 +413,7 @@ static void exit_cond_resched(void)

void irqentry_exit_cond_resched(struct pt_regs *regs)
{
+ arch_restore_aux_pt_regs(regs);
exit_cond_resched();
}

@@ -415,6 +421,10 @@ noinstr void irqentry_exit(struct pt_regs *regs, irqentry_state_t state)
{
lockdep_assert_irqs_disabled();

+ instrumentation_begin();
+ arch_restore_aux_pt_regs(regs);
+ instrumentation_end();
+
/* Check whether this returns to user mode */
if (user_mode(regs)) {
irqentry_exit_to_user_mode(regs);
@@ -464,6 +474,7 @@ irqentry_state_t noinstr irqentry_nmi_enter(struct pt_regs *regs)
instrumentation_begin();
trace_hardirqs_off_finish();
ftrace_nmi_enter();
+ arch_save_aux_pt_regs(regs);
instrumentation_end();

return irq_state;
@@ -472,6 +483,7 @@ irqentry_state_t noinstr irqentry_nmi_enter(struct pt_regs *regs)
void noinstr irqentry_nmi_exit(struct pt_regs *regs, irqentry_state_t irq_state)
{
instrumentation_begin();
+ arch_restore_aux_pt_regs(regs);
ftrace_nmi_exit();
if (irq_state.lockdep) {
trace_hardirqs_on_prepare();
--
2.31.1