linux-kernel - [PATCH V9 25/45] entry: Add calls for save/restore auxiliary pt

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Date:   Thu, 10 Mar 2022 09:19:59 -0800
From:   ira.weiny@...el.com
To:     Dave Hansen <dave.hansen@...ux.intel.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        Dan Williams <dan.j.williams@...el.com>
Cc:     Ira Weiny <ira.weiny@...el.com>, Fenghua Yu <fenghua.yu@...el.com>,
        Rick Edgecombe <rick.p.edgecombe@...el.com>,
        "Shankar, Ravi V" <ravi.v.shankar@...el.com>,
        linux-kernel@...r.kernel.org
Subject: [PATCH V9 25/45] entry: Add calls for save/restore auxiliary pt_regs

From: Ira Weiny <ira.weiny@...el.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.

Add calls to the architecture save and restore auxiliary pt_regs
functions.  Define empty calls for any architecture which does not have
auxiliary pt_regs.

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@...el.com>

---
Changes for V9
	Update commit message

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();
-- 
2.35.1