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Subject[RFC PATCH 2/5] entry: Add calls for save/restore auxiliary pt_regs
Date
From: Ira Weiny <ira.weiny@intel.com>

Some architectures have auxiliary pt_regs space available to store
information on the stack during exceptions. This information is easier
to obtain and store within C code rather than in arch specific assembly.

Define empty calls to architecture specific save and restore auxiliary
pt_regs functions. Call these functions on generic entry/exit.

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().

Cc: Rik van Riel <riel@surriel.com>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Borislav Petkov <bp@alien8.de>
Signed-off-by: Ira Weiny <ira.weiny@intel.com>

---
Forward ported from PKS series
https://lore.kernel.org/lkml/20220419170649.1022246-20-ira.weiny@intel.com/
---
include/linux/entry-common.h | 8 ++++++++
kernel/entry/common.c | 16 ++++++++++++++--
2 files changed, 22 insertions(+), 2 deletions(-)

diff --git a/include/linux/entry-common.h b/include/linux/entry-common.h
index 976cce7cf803..1c09ba64ad28 100644
--- a/include/linux/entry-common.h
+++ b/include/linux/entry-common.h
@@ -79,6 +79,14 @@ static __always_inline void arch_enter_from_user_mode(struct pt_regs *regs);
static __always_inline void arch_enter_from_user_mode(struct pt_regs *regs) {}
#endif

+#ifndef arch_save_aux_pt_regs
+static inline void arch_save_aux_pt_regs(struct pt_regs *regs) { }
+#endif
+
+#ifndef arch_restore_aux_pt_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 8c0f334c4b75..a70a0f314aee 100644
--- a/kernel/entry/common.c
+++ b/kernel/entry/common.c
@@ -317,7 +317,7 @@ 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;
}

/*
@@ -356,7 +356,7 @@ noinstr irqentry_state_t irqentry_enter(struct pt_regs *regs)
instrumentation_end();

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

/*
@@ -371,6 +371,11 @@ 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;
}

@@ -401,6 +406,7 @@ void dynamic_irqentry_exit_cond_resched(void)

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

@@ -408,6 +414,10 @@ 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);
@@ -459,6 +469,7 @@ 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;
@@ -467,6 +478,7 @@ 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();
--
2.35.3
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