Commit c1699302 authored by Abhishek Dubey's avatar Abhishek Dubey Committed by Madhavan Srinivasan
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powerpc64/bpf: Support exceptions 

The modified prologue/epilogue generation code now
enables exception-callback to use the stack frame of
the program marked as exception boundary, where callee
saved registers are stored.

As per ppc64 ABIv2 documentation[1], r14-r31 are callee
saved registers. BPF programs on ppc64 already saves
r26-r31 registers. Saving the remaining set of callee
saved registers(r14-r25) is handled in the next patch.

[1] https://ftp.rtems.org/pub/rtems/people/sebh/ABI64BitOpenPOWERv1.1_16July2015_pub.pdf



Signed-off-by: default avatarAbhishek Dubey <adubey@linux.ibm.com>
Signed-off-by: default avatarMadhavan Srinivasan <maddy@linux.ibm.com>
Link: https://patch.msgid.link/20260124075223.6033-6-adubey@linux.ibm.com
parent b1c24f08

arch/powerpc/net/bpf_jit.h

+2 −0
Original line number Diff line number Diff line
@@ -179,6 +179,8 @@ struct codegen_context { 
	u64 arena_vm_start;

	u64 user_vm_start;

	bool is_subprog;

	bool exception_boundary;

	bool exception_cb;

};



#define bpf_to_ppc(r)	(ctx->b2p[r])

arch/powerpc/net/bpf_jit_comp.c

+7 −0
Original line number Diff line number Diff line
@@ -207,6 +207,8 @@ struct bpf_prog *bpf_int_jit_compile(struct bpf_prog *fp) 
	cgctx.arena_vm_start = bpf_arena_get_kern_vm_start(fp->aux->arena);

	cgctx.user_vm_start = bpf_arena_get_user_vm_start(fp->aux->arena);

	cgctx.is_subprog = bpf_is_subprog(fp);

	cgctx.exception_boundary = fp->aux->exception_boundary;

	cgctx.exception_cb = fp->aux->exception_cb;



	/* Scouting faux-generate pass 0 */

	if (bpf_jit_build_body(fp, NULL, NULL, &cgctx, addrs, 0, false)) {
@@ -436,6 +438,11 @@ void bpf_jit_free(struct bpf_prog *fp) 
	bpf_prog_unlock_free(fp);

}



bool bpf_jit_supports_exceptions(void)

{

	return IS_ENABLED(CONFIG_PPC64);

}



bool bpf_jit_supports_subprog_tailcalls(void)

{

	return IS_ENABLED(CONFIG_PPC64);

arch/powerpc/net/bpf_jit_comp64.c

+41 −18
Original line number Diff line number Diff line
@@ -89,7 +89,9 @@ static inline bool bpf_has_stack_frame(struct codegen_context *ctx) 
	 * - the bpf program uses its stack area

	 * The latter condition is deduced from the usage of BPF_REG_FP

	 */

	return ctx->seen & SEEN_FUNC || bpf_is_seen_register(ctx, bpf_to_ppc(BPF_REG_FP));

	return ctx->seen & SEEN_FUNC ||

	       bpf_is_seen_register(ctx, bpf_to_ppc(BPF_REG_FP)) ||

	       ctx->exception_cb;

}



/*
@@ -161,8 +163,13 @@ void bpf_jit_build_prologue(u32 *image, struct codegen_context *ctx) 
		EMIT(PPC_RAW_LI(bpf_to_ppc(TMP_REG_1), 0));

		/* this goes in the redzone */

		EMIT(PPC_RAW_STD(bpf_to_ppc(TMP_REG_1), _R1, -(BPF_PPC_TAILCALL)));

	} else {

	} else if (!ctx->exception_cb) {

		/*

		 * Tailcall jitting for non exception_cb progs only.

		 * exception_cb won't require tail_call_info to be setup.

		 *

		 * tail_call_info interpretation logic:

		 *

		 * if tail_call_info < MAX_TAIL_CALL_CNT

		 *      main prog calling first subprog -> copy reference

		 * else
@@ -177,8 +184,12 @@ void bpf_jit_build_prologue(u32 *image, struct codegen_context *ctx) 
		EMIT(PPC_RAW_STD(bpf_to_ppc(TMP_REG_1), _R1, -(BPF_PPC_TAILCALL)));

	}



	if (bpf_has_stack_frame(ctx)) {

	if (bpf_has_stack_frame(ctx) && !ctx->exception_cb) {

		/*

		 * exception_cb uses boundary frame after stack walk.

		 * It can simply use redzone, this optimization reduces

		 * stack walk loop by one level.

		 *

		 * We need a stack frame, but we don't necessarily need to

		 * save/restore LR unless we call other functions

		 */
@@ -190,20 +201,32 @@ void bpf_jit_build_prologue(u32 *image, struct codegen_context *ctx) 
		EMIT(PPC_RAW_STDU(_R1, _R1, -(BPF_PPC_STACKFRAME + ctx->stack_size)));

	}



	if (!ctx->exception_cb) {

		/*

		 * Back up non-volatile regs -- BPF registers 6-10

		 * If we haven't created our own stack frame, we save these

		 * in the protected zone below the previous stack frame

		 */

		for (i = BPF_REG_6; i <= BPF_REG_10; i++)

		if (bpf_is_seen_register(ctx, bpf_to_ppc(i)))

			EMIT(PPC_RAW_STD(bpf_to_ppc(i), _R1, bpf_jit_stack_offsetof(ctx, bpf_to_ppc(i))));

			if (ctx->exception_boundary || bpf_is_seen_register(ctx, bpf_to_ppc(i)))

				EMIT(PPC_RAW_STD(bpf_to_ppc(i), _R1,

					bpf_jit_stack_offsetof(ctx, bpf_to_ppc(i))));



	if (ctx->arena_vm_start)

		if (ctx->exception_boundary || ctx->arena_vm_start)

			EMIT(PPC_RAW_STD(bpf_to_ppc(ARENA_VM_START), _R1,

				 bpf_jit_stack_offsetof(ctx, bpf_to_ppc(ARENA_VM_START))));

	} else {

		/*

		 * Exception callback receives Frame Pointer of boundary

		 * program(main prog) as third arg

		 */

		EMIT(PPC_RAW_MR(_R1, _R5));

	}



	/* Setup frame pointer to point to the bpf stack area */

	/*

	 * Exception_cb not restricted from using stack area or arena.

	 * Setup frame pointer to point to the bpf stack area

	 */

	if (bpf_is_seen_register(ctx, bpf_to_ppc(BPF_REG_FP)))

		EMIT(PPC_RAW_ADDI(bpf_to_ppc(BPF_REG_FP), _R1,

			STACK_FRAME_MIN_SIZE + ctx->stack_size));
@@ -218,17 +241,17 @@ static void bpf_jit_emit_common_epilogue(u32 *image, struct codegen_context *ctx 


	/* Restore NVRs */

	for (i = BPF_REG_6; i <= BPF_REG_10; i++)

		if (bpf_is_seen_register(ctx, bpf_to_ppc(i)))

		if (ctx->exception_cb || bpf_is_seen_register(ctx, bpf_to_ppc(i)))

			EMIT(PPC_RAW_LD(bpf_to_ppc(i), _R1, bpf_jit_stack_offsetof(ctx, bpf_to_ppc(i))));



	if (ctx->arena_vm_start)

	if (ctx->exception_cb || ctx->arena_vm_start)

		EMIT(PPC_RAW_LD(bpf_to_ppc(ARENA_VM_START), _R1,

				bpf_jit_stack_offsetof(ctx, bpf_to_ppc(ARENA_VM_START))));



	/* Tear down our stack frame */

	if (bpf_has_stack_frame(ctx)) {

		EMIT(PPC_RAW_ADDI(_R1, _R1, BPF_PPC_STACKFRAME + ctx->stack_size));

		if (ctx->seen & SEEN_FUNC) {

		if (ctx->seen & SEEN_FUNC || ctx->exception_cb) {

			EMIT(PPC_RAW_LD(_R0, _R1, PPC_LR_STKOFF));

			EMIT(PPC_RAW_MTLR(_R0));

		}