From: Borislav Petkov <bp@alien8.de>
To: Peter Zijlstra <peterz@infradead.org>
Cc: x86@kernel.org, jpoimboe@redhat.com, jgross@suse.com,
mbenes@suse.com, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2 02/14] x86/alternatives: Optimize optimize_nops()
Date: Sun, 21 Mar 2021 13:06:47 +0100 [thread overview]
Message-ID: <20210321120647.GB14446@zn.tnic> (raw)
In-Reply-To: <20210318171919.520075106@infradead.org>
On Thu, Mar 18, 2021 at 06:11:05PM +0100, Peter Zijlstra wrote:
> --- a/arch/x86/kernel/alternative.c
> +++ b/arch/x86/kernel/alternative.c
> @@ -345,19 +345,39 @@ recompute_jump(struct alt_instr *a, u8 *
> static void __init_or_module noinline optimize_nops(struct alt_instr *a, u8 *instr)
> {
> unsigned long flags;
> - int i;
> + int nops = 0, i = 0;
> + struct insn insn;
> + u8 *nop = NULL;
>
> - for (i = 0; i < a->padlen; i++) {
> - if (instr[i] != 0x90)
> + do {
> + if (insn_decode_kernel(&insn, &instr[i]))
> return;
> - }
>
> - local_irq_save(flags);
> - add_nops(instr + (a->instrlen - a->padlen), a->padlen);
> - local_irq_restore(flags);
> + if (insn.length == 1 && insn.opcode.bytes[0] == 0x90) {
> + if (!nop) {
> + nop = &instr[i];
> + nops = 1;
> + } else {
> + nops++;
> + }
> + }
> + i += insn.length;
> +
> + if ((insn.length != 1 || i == a->instrlen) && nop) {
> +
> + local_irq_save(flags);
> + add_nops(nop, nops);
> + local_irq_restore(flags);
> +
> + DUMP_BYTES(instr, a->instrlen, "%px: [%d:%d) optimized NOPs: ",
> + instr, (int)(unsigned long)(nop-instr), nops);
> +
> + nop = NULL;
> + }
>
> - DUMP_BYTES(instr, a->instrlen, "%px: [%d:%d) optimized NOPs: ",
> - instr, a->instrlen - a->padlen, a->padlen);
> + } while (i < a->instrlen);
> +
> + WARN_ON_ONCE(nop);
> }
I think I've made this simpler; pasting the whole function and not the
diff because former is easier to read:
/*
* "noinline" to cause control flow change and thus invalidate I$ and
* cause refetch after modification.
*
* Jump over the non-NOP insns, the remaining bytes must be single-byte NOPs,
* optimize them.
*/
static void __init_or_module noinline optimize_nops(struct alt_instr *a, u8 *instr)
{
unsigned long flags;
struct insn insn;
int i = 0, j;
/* Skip preceding non-NOP instructions. */
do {
if (insn_decode_kernel(&insn, &instr[i]))
return;
if (insn.length == 1 && insn.opcode.bytes[0] == 0x90)
break;
i += insn.length;
} while (i < a->instrlen);
if (i >= a->instrlen - 1)
return;
/* Verify rest is NOPs - should not fire(tm) */
for (j = i; j < a->instrlen - 1; j++) {
if (WARN(instr[j] != 0x90, "Wrong insn byte 0x%hx at 0x%px\n",
instr[j], &instr[j]))
return;
}
local_irq_save(flags);
add_nops(&instr[i], a->instrlen - i);
local_irq_restore(flags);
DUMP_BYTES(instr, a->instrlen, "%px: [%d:%d) optimized NOPs: ",
instr, i, a->instrlen);
}
--
Regards/Gruss,
Boris.
https://people.kernel.org/tglx/notes-about-netiquette
next prev parent reply other threads:[~2021-03-21 12:07 UTC|newest]
Thread overview: 45+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-03-18 17:11 [PATCH v2 00/14] x86,objtool: Optimize !RETPOLINE Peter Zijlstra
2021-03-18 17:11 ` [PATCH v2 01/14] x86: Add insn_decode_kernel() Peter Zijlstra
2021-03-19 10:40 ` Borislav Petkov
2021-03-18 17:11 ` [PATCH v2 02/14] x86/alternatives: Optimize optimize_nops() Peter Zijlstra
2021-03-21 12:06 ` Borislav Petkov [this message]
2021-03-22 8:17 ` Peter Zijlstra
2021-03-22 11:07 ` Borislav Petkov
2021-03-18 17:11 ` [PATCH v2 03/14] x86/retpoline: Simplify retpolines Peter Zijlstra
2021-03-19 17:18 ` David Laight
2021-03-22 9:32 ` Peter Zijlstra
2021-03-22 15:41 ` David Laight
2021-03-18 17:11 ` [PATCH v2 04/14] objtool: Correctly handle retpoline thunk calls Peter Zijlstra
2021-03-18 17:11 ` [PATCH v2 05/14] objtool: Per arch retpoline naming Peter Zijlstra
2021-03-19 2:38 ` Josh Poimboeuf
2021-03-19 9:07 ` Peter Zijlstra
2021-03-18 17:11 ` [PATCH v2 06/14] objtool: Fix static_call list generation Peter Zijlstra
2021-03-22 12:44 ` Miroslav Benes
2021-03-18 17:11 ` [PATCH v2 07/14] objtool: Rework rebuild_reloc logic Peter Zijlstra
2021-03-18 17:11 ` [PATCH v2 08/14] objtool: Add elf_create_reloc() helper Peter Zijlstra
2021-03-19 1:42 ` Josh Poimboeuf
2021-03-19 9:47 ` Peter Zijlstra
2021-03-19 15:12 ` Josh Poimboeuf
2021-03-19 15:24 ` Peter Zijlstra
2021-03-19 15:37 ` Josh Poimboeuf
2021-03-18 17:11 ` [PATCH v2 09/14] objtool: Extract elf_strtab_concat() Peter Zijlstra
2021-03-19 2:10 ` Josh Poimboeuf
2021-03-19 9:52 ` Peter Zijlstra
2021-03-18 17:11 ` [PATCH v2 10/14] objtool: Extract elf_symbol_add() Peter Zijlstra
2021-03-19 2:14 ` Josh Poimboeuf
2021-03-19 9:54 ` Peter Zijlstra
2021-03-19 15:04 ` Josh Poimboeuf
2021-03-18 17:11 ` [PATCH v2 11/14] objtool: Add elf_create_undef_symbol() Peter Zijlstra
2021-03-19 2:29 ` Josh Poimboeuf
2021-03-19 7:56 ` Peter Zijlstra
2021-03-18 17:11 ` [PATCH v2 12/14] objtool: Allow archs to rewrite retpolines Peter Zijlstra
2021-03-19 2:54 ` Josh Poimboeuf
2021-03-19 11:21 ` Peter Zijlstra
2021-03-19 13:28 ` Peter Zijlstra
2021-03-18 17:11 ` [PATCH v2 13/14] objtool: Skip magical retpoline .altinstr_replacement Peter Zijlstra
2021-03-18 17:11 ` [PATCH v2 14/14] objtool,x86: Rewrite retpoline thunk calls Peter Zijlstra
2021-03-19 3:29 ` Josh Poimboeuf
2021-03-19 8:06 ` Peter Zijlstra
2021-03-19 15:30 ` Josh Poimboeuf
2021-03-19 15:56 ` Peter Zijlstra
2021-03-19 22:52 ` Josh Poimboeuf
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