linux-kernel - Re: [PATCH 2/3] arm64: use PAGE_KERNEL_ROX directly in alloc_insn

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Message-Id: <20200620191616.bae356186ba3329ade67bbf7@linux-foundation.org>
Date:   Sat, 20 Jun 2020 19:16:16 -0700
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Christoph Hellwig <hch@....de>
Cc:     Dexuan Cui <decui@...rosoft.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>, Jessica Yu <jeyu@...nel.org>,
        x86@...nel.org, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org, linux-hyperv@...r.kernel.org,
        linux-mm@...ck.org
Subject: Re: [PATCH 2/3] arm64: use PAGE_KERNEL_ROX directly in
 alloc_insn_page

On Thu, 18 Jun 2020 08:43:06 +0200 Christoph Hellwig <hch@....de> wrote:

> Use PAGE_KERNEL_ROX directly instead of allocating RWX and setting the
> page read-only just after the allocation.
> 
> --- a/arch/arm64/kernel/probes/kprobes.c
> +++ b/arch/arm64/kernel/probes/kprobes.c
> @@ -120,15 +120,9 @@ int __kprobes arch_prepare_kprobe(struct kprobe *p)
>  
>  void *alloc_insn_page(void)
>  {
> -	void *page;
> -
> -	page = vmalloc_exec(PAGE_SIZE);
> -	if (page) {
> -		set_memory_ro((unsigned long)page, 1);
> -		set_vm_flush_reset_perms(page);
> -	}
> -
> -	return page;
> +	return __vmalloc_node_range(PAGE_SIZE, 1, VMALLOC_START, VMALLOC_END,
> +			GFP_KERNEL, PAGE_KERNEL_ROX, VM_FLUSH_RESET_PERMS,
> +			NUMA_NO_NODE, __func__);
>  }
>  
>  /* arm kprobe: install breakpoint in text */

But why.  I think this is just a cleanup, doesn't address any runtime issue?