From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751954AbdKWMEj convert rfc822-to-8bit (ORCPT ); Thu, 23 Nov 2017 07:04:39 -0500 Received: from ozlabs.org ([103.22.144.67]:39477 "EHLO ozlabs.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751307AbdKWMEi (ORCPT ); Thu, 23 Nov 2017 07:04:38 -0500 From: Michael Ellerman To: Christophe LEROY Cc: Balbir Singh , Benjamin Herrenschmidt , Paul Mackerras , Scott Wood , Meelis Roos , "linux-kernel\@vger.kernel.org" , "open list\:LINUX FOR POWERPC \(32-BIT AND 64-BIT\)" Subject: Re: [PATCH v2] powerpc: fix boot on BOOK3S_32 with CONFIG_STRICT_KERNEL_RWX In-Reply-To: <74521488-5ddb-4fe2-f419-9a9debeaaf0f@c-s.fr> References: <20171121142820.C744F6BB8F@po15668-vm-win7.idsi0.si.c-s.fr> <141a04c4-a236-430d-f346-ad31252e146a@c-s.fr> <87h8tm355i.fsf@concordia.ellerman.id.au> <74521488-5ddb-4fe2-f419-9a9debeaaf0f@c-s.fr> Date: Thu, 23 Nov 2017 23:04:32 +1100 Message-ID: <8760a12obz.fsf@concordia.ellerman.id.au> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8BIT Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Christophe LEROY writes: > Le 22/11/2017 à 12:48, Michael Ellerman a écrit : >> Christophe LEROY writes: >>> Le 22/11/2017 à 00:07, Balbir Singh a écrit : >>>> On Wed, Nov 22, 2017 at 1:28 AM, Christophe Leroy >>>> wrote: >>>>> On powerpc32, patch_instruction() is called by apply_feature_fixups() >>>>> which is called from early_init() ... >>>>> diff --git a/arch/powerpc/lib/code-patching.c b/arch/powerpc/lib/code-patching.c >>>>> index c9de03e0c1f1..d469224c4ada 100644 >>>>> --- a/arch/powerpc/lib/code-patching.c >>>>> +++ b/arch/powerpc/lib/code-patching.c >>>>> @@ -146,11 +147,8 @@ int patch_instruction(unsigned int *addr, unsigned int instr) >>>>> * During early early boot patch_instruction is called >>>>> * when text_poke_area is not ready, but we still need >>>>> * to allow patching. We just do the plain old patching >>>>> - * We use slab_is_available and per cpu read * via this_cpu_read >>>>> - * of text_poke_area. Per-CPU areas might not be up early >>>>> - * this can create problems with just using this_cpu_read() >>>>> */ >>>>> - if (!slab_is_available() || !this_cpu_read(text_poke_area)) >>>>> + if (!this_cpu_read(*PTRRELOC(&text_poke_area))) >>>>> return __patch_instruction(addr, instr); >>>> >>>> On ppc64, we call apply_feature_fixups() in early_setup() after we've >>>> relocated ourselves. Sorry for missing the ppc32 case. I would like to >>>> avoid PTRRELOC when unnecessary. >>> >>> What do you suggest then ? >>> >>> Some #ifdef PPC32 around that ? >> >> No I don't think that improves anything. >> >> I think the comment about per-cpu not being up is wrong, you'll just get >> the static version of text_poke_area, which should be NULL. So we don't >> need the slab_available() check anyway. >> >> So I'll take this as-is. >> >> Having said that I absolutely hate PTRRELOC, so if it starts spreading >> we will have to come up with something less bug prone. > > Would something like that be the solution ? I don't love that actual patch, there's a lot of churn just for one flag. But the idea is not so bad. In fact I don't think we ever need to use the text_poke_area when we call do_feature_fixups(). Most of the calls are in early boot. The exception is for modules, but when we do the fixups *of the module*, the module text is not mapped read only yet. So I think we can just do something like below. cheers diff --git a/arch/powerpc/include/asm/code-patching.h b/arch/powerpc/include/asm/code-patching.h index abef812de7f8..1090024e8519 100644 --- a/arch/powerpc/include/asm/code-patching.h +++ b/arch/powerpc/include/asm/code-patching.h @@ -31,6 +31,7 @@ unsigned int create_cond_branch(const unsigned int *addr, unsigned long target, int flags); int patch_branch(unsigned int *addr, unsigned long target, int flags); int patch_instruction(unsigned int *addr, unsigned int instr); +int raw_patch_instruction(unsigned int *addr, unsigned int instr); int instr_is_relative_branch(unsigned int instr); int instr_is_branch_to_addr(const unsigned int *instr, unsigned long addr); diff --git a/arch/powerpc/lib/code-patching.c b/arch/powerpc/lib/code-patching.c index d469224c4ada..d1eb24cbef58 100644 --- a/arch/powerpc/lib/code-patching.c +++ b/arch/powerpc/lib/code-patching.c @@ -23,7 +23,7 @@ #include #include -static int __patch_instruction(unsigned int *addr, unsigned int instr) +int raw_patch_instruction(unsigned int *addr, unsigned int instr) { int err; @@ -148,8 +148,8 @@ int patch_instruction(unsigned int *addr, unsigned int instr) * when text_poke_area is not ready, but we still need * to allow patching. We just do the plain old patching */ - if (!this_cpu_read(*PTRRELOC(&text_poke_area))) - return __patch_instruction(addr, instr); + if (!this_cpu_read(text_poke_area)) + return raw_patch_instruction(addr, instr); local_irq_save(flags); @@ -184,7 +184,7 @@ int patch_instruction(unsigned int *addr, unsigned int instr) int patch_instruction(unsigned int *addr, unsigned int instr) { - return __patch_instruction(addr, instr); + return raw_patch_instruction(addr, instr); } #endif /* CONFIG_STRICT_KERNEL_RWX */ diff --git a/arch/powerpc/lib/feature-fixups.c b/arch/powerpc/lib/feature-fixups.c index 41cf5ae273cf..0872d60ede10 100644 --- a/arch/powerpc/lib/feature-fixups.c +++ b/arch/powerpc/lib/feature-fixups.c @@ -62,7 +62,7 @@ static int patch_alt_instruction(unsigned int *src, unsigned int *dest, } } - patch_instruction(dest, instr); + raw_patch_instruction(dest, instr); return 0; } @@ -91,7 +91,7 @@ static int patch_feature_section(unsigned long value, struct fixup_entry *fcur) } for (; dest < end; dest++) - patch_instruction(dest, PPC_INST_NOP); + raw_patch_instruction(dest, PPC_INST_NOP); return 0; } @@ -129,7 +129,7 @@ void do_lwsync_fixups(unsigned long value, void *fixup_start, void *fixup_end) for (; start < end; start++) { dest = (void *)start + *start; - patch_instruction(dest, PPC_INST_LWSYNC); + raw_patch_instruction(dest, PPC_INST_LWSYNC); } } @@ -147,7 +147,7 @@ static void do_final_fixups(void) length = (__end_interrupts - _stext) / sizeof(int); while (length--) { - patch_instruction(dest, *src); + raw_patch_instruction(dest, *src); src++; dest++; }