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Subject: Re: [PATCH v2 01/17] mm/gup: Fixup p*_access_permitted()
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From: Dave Hansen <dave.hansen@intel.com>
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Date: Fri, 15 Dec 2017 17:25:20 -0800
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To: Linus Torvalds <torvalds@linux-foundation.org>, Dan Williams <dan.j.williams@intel.com>
Cc: Peter Zijlstra <peterz@infradead.org>, Linux Kernel Mailing List <linux-kernel@vger.kernel.org>, Thomas Gleixner <tglx@linutronix.de>, the arch/x86 maintainers <x86@kernel.org>, Andy Lutomirsky <luto@kernel.org>, Borislav Petkov <bpetkov@suse.de>, Greg KH <gregkh@linuxfoundation.org>, Kees Cook <keescook@google.com>, Hugh Dickins <hughd@google.com>, Brian Gerst <brgerst@gmail.com>, Josh Poimboeuf <jpoimboe@redhat.com>, Denys Vlasenko <dvlasenk@redhat.com>, Boris Ostrovsky <boris.ostrovsky@oracle.com>, Juergen Gross <jgross@suse.com>, David Laight <David.Laight@aculab.com>, Eduardo Valentin <eduval@amazon.com>, "Liguori, Anthony" <aliguori@amazon.com>, Will Deacon <will.deacon@arm.com>, linux-mm <linux-mm@kvack.org>, "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>

On 12/15/2017 05:10 PM, Linus Torvalds wrote:
> Because *if* we want to check protection keys, I think we should do
> that at the vma layer, partly exactly because the exact implementation
> of protection keys is so architecture-specific, and partly because I
> don't think it makes sense to check them for every page anyway.

So, there are VMA checks against protection keys.  The problem _here_ is
that we are checking against the VMA (and correctly skipping the PKRU
checks) and then _mistakenly_ applying the PTE checks against PKRU.

I think the reason we needed VMA and PTE checks was the
get_user_pages_fast() path not having a VMA.

I need to go re-read the commits, though.

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