Merge branch 'support-bpf_fastcall-patterns-for-calls-to-kfuncs'

Eduard Zingerman says:

====================
support bpf_fastcall patterns for calls to kfuncs

As an extension of [1], allow bpf_fastcall patterns for kfuncs:
- pattern rules are the same as for helpers;
- spill/fill removal is allowed only for kfuncs listed in the
  is_fastcall_kfunc_call (under assumption that such kfuncs would
  always be members of special_kfunc_list).

Allow bpf_fastcall rewrite for bpf_cast_to_kern_ctx() and
bpf_rdonly_cast() in order to conjure selftests for this feature.

After this patch-set verifier would rewrite the program below:

  r2 = 1
  *(u64 *)(r10 - 32) = r2
  call %[bpf_cast_to_kern_ctx]
  r2 = *(u64 *)(r10 - 32)
  r0 = r2;"

As follows:

  r2 = 1   /* spill/fill at r10[-32] is removed */
  r0 = r1  /* replacement for bpf_cast_to_kern_ctx() */
  r0 = r2
  exit

Also, attribute used by LLVM implementation of the feature had been
changed from no_caller_saved_registers to bpf_fastcall (see [2]).
This patch-set replaces references to nocsr by references to
bpf_fastcall to keep LLVM and Kernel parts in sync.

[1] no_caller_saved_registers attribute for helper calls
    https://lore.kernel.org/bpf/[email protected]/
[2] [BPF] introduce __attribute__((bpf_fastcall))
    llvm/llvm-project#105417

Changes v2->v3:
- added a patch fixing arch_mask handling in test_loader,
  otherwise newly added tests for the feature were skipped
  (a fix for regression introduced by a recent commit);
- fixed warning regarding unused 'params' variable;
- applied stylistical fixes suggested by Yonghong;
- added acks from Yonghong;

Changes v1->v2:
- added two patches replacing all mentions of nocsr by bpf_fastcall
  (suggested by Andrii);
- removed KF_NOCSR flag (suggested by Yonghong).

v1: https://lore.kernel.org/bpf/[email protected]/
v2: https://lore.kernel.org/bpf/[email protected]/
====================

Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Alexei Starovoitov <[email protected]>

Author: Alexei Starovoitov

include/linux/bpf.h

@@ -808,12 +808,12 @@ struct bpf_func_proto {
 	bool gpl_only;
 	bool pkt_access;
 	bool might_sleep;
-	/* set to true if helper follows contract for gcc/llvm
-	 * attribute no_caller_saved_registers:
+	/* set to true if helper follows contract for llvm
+	 * attribute bpf_fastcall:
 	 * - void functions do not scratch r0
 	 * - functions taking N arguments scratch only registers r1-rN
 	 */
-	bool allow_nocsr;
+	bool allow_fastcall;
 	enum bpf_return_type ret_type;
 	union {
 		struct {

include/linux/bpf_verifier.h

@@ -577,13 +577,13 @@ struct bpf_insn_aux_data {
 	bool call_with_percpu_alloc_ptr; /* {this,per}_cpu_ptr() with prog percpu alloc */
 	u8 alu_state; /* used in combination with alu_limit */
 	/* true if STX or LDX instruction is a part of a spill/fill
-	 * pattern for a no_caller_saved_registers call.
+	 * pattern for a bpf_fastcall call.
 	 */
-	u8 nocsr_pattern:1;
+	u8 fastcall_pattern:1;
 	/* for CALL instructions, a number of spill/fill pairs in the
-	 * no_caller_saved_registers pattern.
+	 * bpf_fastcall pattern.
 	 */
-	u8 nocsr_spills_num:3;
+	u8 fastcall_spills_num:3;
 
 	/* below fields are initialized once */
 	unsigned int orig_idx; /* original instruction index */
@@ -653,19 +653,19 @@ struct bpf_subprog_info {
 	u32 linfo_idx; /* The idx to the main_prog->aux->linfo */
 	u16 stack_depth; /* max. stack depth used by this function */
 	u16 stack_extra;
-	/* offsets in range [stack_depth .. nocsr_stack_off)
-	 * are used for no_caller_saved_registers spills and fills.
+	/* offsets in range [stack_depth .. fastcall_stack_off)
+	 * are used for bpf_fastcall spills and fills.
 	 */
-	s16 nocsr_stack_off;
+	s16 fastcall_stack_off;
 	bool has_tail_call: 1;
 	bool tail_call_reachable: 1;
 	bool has_ld_abs: 1;
 	bool is_cb: 1;
 	bool is_async_cb: 1;
 	bool is_exception_cb: 1;
 	bool args_cached: 1;
-	/* true if nocsr stack region is used by functions that can't be inlined */
-	bool keep_nocsr_stack: 1;
+	/* true if bpf_fastcall stack region is used by functions that can't be inlined */
+	bool keep_fastcall_stack: 1;
 
 	u8 arg_cnt;
 	struct bpf_subprog_arg_info args[MAX_BPF_FUNC_REG_ARGS];

kernel/bpf/helpers.c

@@ -158,7 +158,7 @@ const struct bpf_func_proto bpf_get_smp_processor_id_proto = {
 	.func		= bpf_get_smp_processor_id,
 	.gpl_only	= false,
 	.ret_type	= RET_INTEGER,
-	.allow_nocsr	= true,
+	.allow_fastcall	= true,
 };
 
 BPF_CALL_0(bpf_get_numa_node_id)