LoongArch: BPF: Fix check condition to call lu32id in move_imm()

As the code comment says, the initial aim is to reduce one instruction
in some corner cases, if bit[51:31] is all 0 or all 1, no need to call
lu32id. That is to say, it should call lu32id only if bit[51:31] is not
all 0 and not all 1. The current code always call lu32id, the result is
right but the logic is unexpected and wrong, fix it.

Cc: stable@vger.kernel.org # 6.1
Fixes: 5dc615520c4d ("LoongArch: Add BPF JIT support")
Reported-by: Colin King (gmail) <colin.i.king@gmail.com>
Closes: https://lore.kernel.org/all/bcf97046-e336-712a-ac68-7fd194f2953e@gmail.com/
Signed-off-by: Tiezhu Yang <yangtiezhu@loongson.cn>
Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>

LoongArch, bpf: Use 4 instructions for function address in JIT

This patch fixes the following issue of function calls in JIT, like:

[ 29.346981] multi-func JIT bug 105 != 103

The issus can be reproduced by running the "inline simple bpf_loop call"
verifier test.

This is because we are emiting 2-4 instructions for 64-bit immediate moves.
During the first pass of JIT, the placeholder address is zero, emiting two
instructions for it. In the extra pass, the function address is in XKVRANGE,
emiting four instructions for it. This change the instruction index in
JIT context. Let's always use 4 instructions for function address in JIT.
So that the instruction sequences don't change between the first pass and
the extra pass for function calls.

Fixes: 5dc615520c4d ("LoongArch: Add BPF JIT support")
Signed-off-by: Hengqi Chen <hengqi.chen@gmail.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Tested-by: Tiezhu Yang <yangtiezhu@loongson.cn>
Link: https://lore.kernel.org/bpf/20230214152633.2265699-1-hengqi.chen@gmail.com

LoongArch: BPF: Add BPF exception tables

Inspired by commit 800834285361("bpf, arm64: Add BPF exception tables"),
do similar to LoongArch to add BPF exception tables.

When a tracing BPF program attempts to read memory without using the
bpf_probe_read() helper, the verifier marks the load instruction with
the BPF_PROBE_MEM flag. Since the LoongArch JIT does not currently
recognize this flag it falls back to the interpreter.

Add support for BPF_PROBE_MEM, by appending an exception table to the
BPF program. If the load instruction causes a data abort, the fixup
infrastructure finds the exception table and fixes up the fault, by
clearing the destination register and jumping over the faulting
instruction.

To keep the compact exception table entry format, inspect the pc in
fixup_exception(). A more generic solution would add a "handler" field
to the table entry, like on x86, s390 and arm64, etc.

Signed-off-by: Youling Tang <tangyouling@loongson.cn>
Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>

LoongArch: Add BPF JIT support

BPF programs are normally handled by a BPF interpreter, add BPF JIT
support for LoongArch to allow the kernel to generate native code when
a program is loaded into the kernel. This will significantly speed-up
processing of BPF programs.

Co-developed-by: Youling Tang <tangyouling@loongson.cn>
Signed-off-by: Youling Tang <tangyouling@loongson.cn>
Signed-off-by: Tiezhu Yang <yangtiezhu@loongson.cn>
Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>