linux-kernel - Re: [PATCH 12/30] x86, kaiser: map GDT into user page tables

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Date:   Tue, 21 Nov 2017 16:37:07 -0800
From:   Dave Hansen <dave.hansen@...ux.intel.com>
To:     Andy Lutomirski <luto@...nel.org>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        moritz.lipp@...k.tugraz.at,
        Daniel Gruss <daniel.gruss@...k.tugraz.at>,
        michael.schwarz@...k.tugraz.at, richard.fellner@...dent.tugraz.at,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Kees Cook <keescook@...gle.com>,
        Hugh Dickins <hughd@...gle.com>, X86 ML <x86@...nel.org>
Subject: Re: [PATCH 12/30] x86, kaiser: map GDT into user page tables

On 11/21/2017 04:17 PM, Andy Lutomirski wrote:
> On Tue, Nov 21, 2017 at 3:42 PM, Dave Hansen
> unsigned long start = (unsigned long)get_cpu_entry_area(cpu);
> for (unsigned long addr = start; addr < start + sizeof(struct
> cpu_entry_area); addr += PAGE_SIZE) {
>   pte_t pte = *pte_offset_k(addr);  /* or however you do this */
>   kaiser_add_mapping(pte_pfn(pte), pte_prot(pte));
> }
> 
> modulo the huge pile of typos in there that surely exist.

That would work.  I just need to find a suitable pte_offset_k() in the
kernel and make sure it works for these purposes.  We probably have one.

> But I still prefer my approach of just sharing the cpu_entry_area pmd
> entries between the user and kernel tables.

That would be spiffy.