linux-kernel - Re: [PATCH 05/11] x86/mm: do not auto-massage page protections

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Date:   Fri, 23 Mar 2018 12:38:07 -0700
From:   Dave Hansen <dave.hansen@...ux.intel.com>
To:     Nadav Amit <namit@...are.com>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        "open list:MEMORY MANAGEMENT" <linux-mm@...ck.org>,
        Andrea Arcangeli <aarcange@...hat.com>,
        "luto@...nel.org" <luto@...nel.org>,
        "torvalds@...ux-foundation.org" <torvalds@...ux-foundation.org>,
        "keescook@...gle.com" <keescook@...gle.com>,
        "hughd@...gle.com" <hughd@...gle.com>,
        "jgross@...e.com" <jgross@...e.com>,
        "x86@...nel.org" <x86@...nel.org>
Subject: Re: [PATCH 05/11] x86/mm: do not auto-massage page protections

On 03/23/2018 12:34 PM, Nadav Amit wrote:
>>>> +	/* mmdebug.h can not be included here because of dependencies */
>>>> +#ifdef CONFIG_DEBUG_VM
>>>> +	WARN_ONCE(pgprot_val(pgprot) != massaged_val,
>>>> +		  "attempted to set unsupported pgprot: %016lx "
>>>> +		  "bits: %016lx supported: %016lx\n",
>>>> +		  pgprot_val(pgprot),
>>>> +		  pgprot_val(pgprot) ^ massaged_val,
>>>> +		  __supported_pte_mask);
>>>> +#endif
>>> Why not to use VM_WARN_ON_ONCE() and avoid the ifdef?
>> I wanted a message.  VM_WARN_ON_ONCE() doesn't let you give a message.
> Right (my bad). But VM_WARN_ONCE() lets you.

I put a comment in up there about this ^^.  #including mmdebug.h caused
dependency problems, so I basically just reimplemented it using
WARN_ONCE() and an #ifdef.