linux-kernel - Re: [RFC][PATCH 05/10] x86/mm: do not auto-massage page protections

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Message-ID: <5659D3EF-CF51-4B1B-8306-CA2559A75789@vmware.com>
Date:   Thu, 22 Feb 2018 21:46:44 +0000
From:   Nadav Amit <namit@...are.com>
To:     Dave Hansen <dave.hansen@...ux.intel.com>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "aarcange@...hat.com" <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: [RFC][PATCH 05/10] x86/mm: do not auto-massage page protections

Dave Hansen <dave.hansen@...ux.intel.com> wrote:

> 
> From: Dave Hansen <dave.hansen@...ux.intel.com>
> 
> 
> +static inline pgprotval_t check_pgprot(pgprot_t pgprot)
> +{
> +	pgprotval_t massaged_val = massage_pgprot(pgprot);
> +
> +	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);

Perhaps use VM_WARN_ONCE instead to avoid any overhead on production
systems?