linux-kernel - Re: [PATCH 12/13] x86/jitalloc: prepare to allocate exectuatble memory as ROX

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Message-ID: <ZHja0HOUabUxD5YS@moria.home.lan>
Date:   Thu, 1 Jun 2023 13:52:16 -0400
From:   Kent Overstreet <kent.overstreet@...ux.dev>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Mike Rapoport <rppt@...nel.org>, linux-kernel@...r.kernel.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Christophe Leroy <christophe.leroy@...roup.eu>,
        "David S. Miller" <davem@...emloft.net>,
        Dinh Nguyen <dinguyen@...nel.org>,
        Heiko Carstens <hca@...ux.ibm.com>,
        Helge Deller <deller@....de>,
        Huacai Chen <chenhuacai@...nel.org>,
        Luis Chamberlain <mcgrof@...nel.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        "Naveen N. Rao" <naveen.n.rao@...ux.ibm.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Russell King <linux@...linux.org.uk>,
        Song Liu <song@...nel.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
        Thomas Gleixner <tglx@...utronix.de>,
        Will Deacon <will@...nel.org>, bpf@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-mips@...r.kernel.org,
        linux-mm@...ck.org, linux-modules@...r.kernel.org,
        linux-parisc@...r.kernel.org, linux-riscv@...ts.infradead.org,
        linux-s390@...r.kernel.org, linux-trace-kernel@...r.kernel.org,
        linuxppc-dev@...ts.ozlabs.org, loongarch@...ts.linux.dev,
        netdev@...r.kernel.org, sparclinux@...r.kernel.org, x86@...nel.org
Subject: Re: [PATCH 12/13] x86/jitalloc: prepare to allocate exectuatble
 memory as ROX

On Thu, Jun 01, 2023 at 12:30:50PM +0200, Peter Zijlstra wrote:
> On Thu, Jun 01, 2023 at 01:12:56PM +0300, Mike Rapoport wrote:
> 
> > +static void __init_or_module do_text_poke(void *addr, const void *opcode, size_t len)
> > +{
> > +	if (system_state < SYSTEM_RUNNING) {
> > +		text_poke_early(addr, opcode, len);
> > +	} else {
> > +		mutex_lock(&text_mutex);
> > +		text_poke(addr, opcode, len);
> > +		mutex_unlock(&text_mutex);
> > +	}
> > +}
> 
> So I don't much like do_text_poke(); why?

Could you share why?

I think the impementation sucks but conceptually it's the right idea -
create a new temporary mapping to avoid the need for RWX mappings.