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Subject: Re: [PATCH 5/5] x86, pti: filter at vma->vm_page_prot population
To:     Nadav Amit <namit@vmware.com>
References: <20180420222018.E7646EE1@viggo.jf.intel.com>
 <20180420222028.99D72858@viggo.jf.intel.com>
 <295DB0D1-CDFB-482C-93DF-63DAA36DAE22@vmware.com>
Cc:     LKML <linux-kernel@vger.kernel.org>,
        "open list:MEMORY MANAGEMENT" <linux-mm@kvack.org>,
        Fengguang Wu <fengguang.wu@intel.com>,
        Andrea Arcangeli <aarcange@redhat.com>,
        Andy Lutomirski <luto@kernel.org>,
        Arjan van de Ven <arjan@linux.intel.com>,
        Borislav Petkov <bp@alien8.de>,
        Dan Williams <dan.j.williams@intel.com>,
        David Woodhouse <dwmw2@infradead.org>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        "hughd@google.com" <hughd@google.com>,
        "jpoimboe@redhat.com" <jpoimboe@redhat.com>,
        "jgross@suse.com" <jgross@suse.com>,
        "keescook@google.com" <keescook@google.com>,
        "torvalds@linux-foundation.org" <torvalds@linux-foundation.org>,
        "peterz@infradead.org" <peterz@infradead.org>,
        "tglx@linutronix.de" <tglx@linutronix.de>,
        "mingo@kernel.org" <mingo@kernel.org>
From:   Dave Hansen <dave.hansen@linux.intel.com>
Message-ID: <30d4fd5a-a82f-2a94-e8cb-ad9b7d2dc5e7@linux.intel.com>
Date:   Mon, 23 Apr 2018 04:37:24 -0700
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On 04/20/2018 06:21 PM, Nadav Amit wrote:
>> pgprot_t vm_get_page_prot(unsigned long vm_flags)
>> {
>> -	return __pgprot(pgprot_val(protection_map[vm_flags &
>> +	pgprot_t ret = __pgprot(pgprot_val(protection_map[vm_flags &
>> 				(VM_READ|VM_WRITE|VM_EXEC|VM_SHARED)]) |
>> 			pgprot_val(arch_vm_get_page_prot(vm_flags)));
>> +
>> +	return arch_filter_pgprot(ret);
>> }
>> EXPORT_SYMBOL(vm_get_page_prot);
> Wouldn’t it be simpler or at least cleaner to change the protection map if
> NX is not supported? I presume it can be done paging_init() similarly to the
> way other archs (e.g., arm, mips) do.

I thought about it, but doing it there requires getting the _timing_
right.  You have to do it before the protection map gets used but after
__supported_pte_mask is totally initialized.  This seemed more
straightforward, especially as a bug fix.

What you are talking about might be a good cleanup, though.