From: ebiederm@xmission.com (Eric W. Biederman)
To: Dave Hansen <dave@sr71.net>
Cc: Linus Torvalds <torvalds@linux-foundation.org>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
the arch/x86 maintainers <x86@kernel.org>,
linux-mm <linux-mm@kvack.org>,
Andrew Morton <akpm@linux-foundation.org>,
Borislav Petkov <bp@alien8.de>, Andi Kleen <ak@linux.intel.com>,
Michal Hocko <mhocko@suse.com>,
Dave Hansen <dave.hansen@linux.intel.com>
Subject: Re: [PATCH 6/6] x86: Fix stray A/D bit setting into non-present PTEs
Date: Fri, 01 Jul 2016 13:12:55 -0500 [thread overview]
Message-ID: <878txlb520.fsf@x220.int.ebiederm.org> (raw)
In-Reply-To: <57769188.9060708@sr71.net> (Dave Hansen's message of "Fri, 1 Jul 2016 08:51:36 -0700")
Dave Hansen <dave@sr71.net> writes:
> On 07/01/2016 07:25 AM, Eric W. Biederman wrote:
>> Linus Torvalds <torvalds@linux-foundation.org> writes:
>>> > On Thu, Jun 30, 2016 at 9:39 PM, Dave Hansen <dave@sr71.net> wrote:
>>>> >>
>>>> >> I think what you suggest will work if we don't consider A/D in
>>>> >> pte_none(). I think there are a bunch of code path where assume that
>>>> >> !pte_present() && !pte_none() means swap.
>>> >
>>> > Yeah, we would need to change pte_none() to mask off D/A, but I think
>>> > that might be the only real change needed (other than making sure that
>>> > we don't use the bits in the swap entries, I didn't look at that part
>>> > at all)
>> It looks like __pte_to_swp_entry also needs to be changed to mask out
>> those bits when the swap code reads pte entries. For all of the same
>> reasons as pte_none.
>
> I guess that would be nice, but isn't it redundant?
>
> static inline swp_entry_t pte_to_swp_entry(pte_t pte)
> {
> ...
> arch_entry = __pte_to_swp_entry(pte);
> return swp_entry(__swp_type(arch_entry), __swp_offset(arch_entry));
> }
>
> As long as __swp_type() and __swp_offset() don't let A/D through, then
> we should be OK. This site is the only call to __pte_to_swp_entry()
> that I can find in the entire codebase.
>
> Or am I missing something?
Given that __pte_to_swp_entry on x86_64 is just __pte_val or pte.pte it
does no filtering. Similarly __swp_type(arch_entry) is a >> and
swp_entry(type, ...) is a << of what appears to be same amount
for the swap type.
So any corruption in the upper bits of the pte will be preserved as a
swap type.
In fact I strongly suspect that the compiler can optimize out all of the
work done by "swp_entry(__swp_type(arch_entry), _swp_offset(arch_entry))".
Eric
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next prev parent reply other threads:[~2016-07-01 18:25 UTC|newest]
Thread overview: 26+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-07-01 0:12 [PATCH 0/6] [v3] Workaround for Xeon Phi PTE A/D bits erratum Dave Hansen
2016-07-01 0:12 ` [PATCH 1/6] x86: fix duplicated X86_BUG(9) macro Dave Hansen
2016-07-01 9:23 ` Borislav Petkov
2016-07-01 16:30 ` Andy Lutomirski
2016-07-01 16:46 ` Borislav Petkov
2016-07-03 14:36 ` Andy Lutomirski
2016-07-03 18:44 ` Borislav Petkov
2016-07-01 0:12 ` [PATCH 2/6] mm, tlb: add mmu_gather->saw_unset_a_or_d Dave Hansen
2016-07-01 0:12 ` [PATCH 3/6] mm: add force_batch_flush to mmu_gather Dave Hansen
2016-07-01 0:12 ` [PATCH 4/6] mm: move flush in madvise_free_pte_range() Dave Hansen
2016-07-01 0:12 ` [PATCH 5/6] mm: make tlb_flush_mmu_tlbonly() return whether it flushed Dave Hansen
2016-07-01 0:12 ` [PATCH 6/6] x86: Fix stray A/D bit setting into non-present PTEs Dave Hansen
2016-07-01 1:50 ` Nadav Amit
2016-07-01 1:54 ` Dave Hansen
2016-07-01 2:55 ` Linus Torvalds
2016-07-01 3:06 ` Brian Gerst
2016-07-01 3:21 ` Linus Torvalds
2016-07-03 17:10 ` Dave Hansen
2016-07-01 4:39 ` Dave Hansen
2016-07-01 5:43 ` Linus Torvalds
2016-07-01 14:25 ` Eric W. Biederman
2016-07-01 15:51 ` Dave Hansen
2016-07-01 18:12 ` Eric W. Biederman [this message]
2016-07-01 16:07 ` Linus Torvalds
2016-07-01 16:14 ` Dave Hansen
2016-07-01 16:25 ` Linus Torvalds
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