Introduce a kernel-private BPF_ST | BPF_IRQ instruction with save and
restore operations. Encode the flags-pointer register in dst_reg and the
operation in imm, leaving src_reg and off reserved as zero.

Add a JIT capability hook whose default implementation declines support,
plus disassembler output for both operations. Architecture backends opt
in separately, and the verifier starts emitting the instructions in a
later patch.

Signed-off-by: Emil Tsalapatis <emil@etsalapatis.com>
---
 include/linux/filter.h | 13 +++++++++++++
 kernel/bpf/core.c      |  5 +++++
 kernel/bpf/disasm.c    |  8 ++++++++
 3 files changed, 26 insertions(+)

diff --git a/include/linux/filter.h b/include/linux/filter.h
index e0218e677a1d..bf67dfa19c17 100644
--- a/include/linux/filter.h
+++ b/include/linux/filter.h
@@ -90,6 +90,10 @@ struct ctl_table_header;
  */
 #define BPF_NOSPEC	0xc0
 
+#define BPF_IRQ		0xe0
+#define BPF_IRQ_SAVE	0
+#define BPF_IRQ_RESTORE	1
+
 /* As per nm, we expose JITed images as text (code) section for
  * kallsyms. That way, tools like perf can find it to match
  * addresses.
@@ -598,6 +602,14 @@ static inline int bpf_atomic_load_reg(const struct bpf_insn *insn)
 		.off   = 0,					\
 		.imm   = 0 })
 
+#define BPF_IRQ_INSN(OP, FLAGS_REG)				\
+	((struct bpf_insn) {					\
+		.code  = BPF_ST | BPF_IRQ,			\
+		.dst_reg = FLAGS_REG,				\
+		.src_reg = 0,					\
+		.off   = 0,					\
+		.imm   = OP })
+
 /* Internal classic blocks for direct assignment */
 
 #define __BPF_STMT(CODE, K)					\
@@ -1277,6 +1289,7 @@ bool bpf_jit_needs_zext(void);
 bool bpf_jit_inlines_helper_call(s32 imm);
 bool bpf_jit_supports_subprog_tailcalls(void);
 bool bpf_jit_supports_percpu_insn(void);
+bool bpf_jit_supports_irq_save_restore(void);
 bool bpf_jit_supports_kfunc_call(void);
 bool bpf_jit_supports_callx(void);
 bool bpf_jit_supports_kfunc_ret_reg_pair(void);
diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c
index 3030beb531d9..0ab9a210e1e8 100644
--- a/kernel/bpf/core.c
+++ b/kernel/bpf/core.c
@@ -3383,6 +3383,11 @@ bool __weak bpf_jit_supports_percpu_insn(void)
 	return false;
 }
 
+bool __weak bpf_jit_supports_irq_save_restore(void)
+{
+	return false;
+}
+
 bool __weak bpf_jit_supports_kfunc_call(void)
 {
 	return false;
diff --git a/kernel/bpf/disasm.c b/kernel/bpf/disasm.c
index 889fc074496f..125e2c5754e9 100644
--- a/kernel/bpf/disasm.c
+++ b/kernel/bpf/disasm.c
@@ -9,6 +9,9 @@
 
 /* Only defined by the non-UAPI linux/filter.h, which this file cannot use. */
 #define BPF_PROBE_ATOMIC 0xe0
+#define BPF_IRQ 0xe0
+#define BPF_IRQ_SAVE 0
+#define BPF_IRQ_RESTORE 1
 
 #define __BPF_FUNC_STR_FN(x) [BPF_FUNC_ ## x] = __stringify(bpf_ ## x)
 static const char * const func_id_str[] = {
@@ -294,6 +297,11 @@ void print_bpf_insn(const struct bpf_insn_cbs *cbs,
 				insn->off, insn->imm);
 		} else if (BPF_MODE(insn->code) == 0xc0 /* BPF_NOSPEC, no UAPI */) {
 			verbose(cbs->private_data, "(%02x) nospec", insn->code);
+		} else if (insn->code == (BPF_ST | BPF_IRQ) &&
+			   (insn->imm == BPF_IRQ_SAVE || insn->imm == BPF_IRQ_RESTORE)) {
+			verbose(cbs->private_data, "(%02x) bpf_local_irq_%s(r%d)",
+				insn->code, insn->imm == BPF_IRQ_SAVE ? "save" : "restore",
+				insn->dst_reg);
 		} else {
 			verbose(cbs->private_data, "BUG_st_%02x", insn->code);
 		}
-- 
2.52.0