LKML Archive on lore.kernel.org
 help / color / Atom feed
From: Andy Lutomirski <luto@kernel.org>
To: "Kirill A. Shutemov" <kirill@shutemov.name>
Cc: Andy Lutomirski <luto@kernel.org>,
	Konstantin Khlebnikov <khlebnikov@yandex-team.ru>,
	Dave Hansen <dave.hansen@intel.com>, X86 ML <x86@kernel.org>,
	Borislav Petkov <bp@alien8.de>,
	Neil Berrington <neil.berrington@datacore.com>,
	LKML <linux-kernel@vger.kernel.org>,
	stable <stable@vger.kernel.org>
Subject: Re: [PATCH v2 1/2] x86/mm/64: Fix vmapped stack syncing on very-large-memory 4-level systems
Date: Fri, 26 Jan 2018 11:02:08 -0800
Message-ID: <CALCETrUaHysYacCF1t_Sap0jHhqBUb7dUKjaVDtPyM-kUMR3sw@mail.gmail.com> (raw)
In-Reply-To: <20180126185143.dx7emh7cq5pbrkxn@node.shutemov.name>

On Fri, Jan 26, 2018 at 10:51 AM, Kirill A. Shutemov
<kirill@shutemov.name> wrote:
> On Thu, Jan 25, 2018 at 01:12:14PM -0800, Andy Lutomirski wrote:
>> Neil Berrington reported a double-fault on a VM with 768GB of RAM that
>> uses large amounts of vmalloc space with PTI enabled.
>>
>> The cause is that load_new_mm_cr3() was never fixed to take the
>> 5-level pgd folding code into account, so, on a 4-level kernel, the
>> pgd synchronization logic compiles away to exactly nothing.
>
> Ouch. Sorry for this.
>
>>
>> Interestingly, the problem doesn't trigger with nopti.  I assume this
>> is because the kernel is mapped with global pages if we boot with
>> nopti.  The sequence of operations when we create a new task is that
>> we first load its mm while still running on the old stack (which
>> crashes if the old stack is unmapped in the new mm unless the TLB
>> saves us), then we call prepare_switch_to(), and then we switch to the
>> new stack.  prepare_switch_to() pokes the new stack directly, which
>> will populate the mapping through vmalloc_fault().  I assume that
>> we're getting lucky on non-PTI systems -- the old stack's TLB entry
>> stays alive long enough to make it all the way through
>> prepare_switch_to() and switch_to() so that we make it to a valid
>> stack.
>>
>> Fixes: b50858ce3e2a ("x86/mm/vmalloc: Add 5-level paging support")
>> Cc: stable@vger.kernel.org
>> Reported-and-tested-by: Neil Berrington <neil.berrington@datacore.com>
>> Signed-off-by: Andy Lutomirski <luto@kernel.org>
>> ---
>>  arch/x86/mm/tlb.c | 34 +++++++++++++++++++++++++++++-----
>>  1 file changed, 29 insertions(+), 5 deletions(-)
>>
>> diff --git a/arch/x86/mm/tlb.c b/arch/x86/mm/tlb.c
>> index a1561957dccb..5bfe61a5e8e3 100644
>> --- a/arch/x86/mm/tlb.c
>> +++ b/arch/x86/mm/tlb.c
>> @@ -151,6 +151,34 @@ void switch_mm(struct mm_struct *prev, struct mm_struct *next,
>>       local_irq_restore(flags);
>>  }
>>
>> +static void sync_current_stack_to_mm(struct mm_struct *mm)
>> +{
>> +     unsigned long sp = current_stack_pointer;
>> +     pgd_t *pgd = pgd_offset(mm, sp);
>> +
>> +     if (CONFIG_PGTABLE_LEVELS > 4) {
>
> Can we have
>
>         if (PTRS_PER_P4D > 1)
>
> here instead? This way I wouldn't need to touch the code again for
> boot-time switching support.

Want to send a patch?

(Also, I haven't noticed a patch to fix up the SYSRET checking for
boot-time switching.  Have I just missed it?)

--Andy

  reply index

Thread overview: 12+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-01-25 21:12 [PATCH v2 0/2] x86/mm/64: vmalloc pgd synchronization cleanups/fixes Andy Lutomirski
2018-01-25 21:12 ` [PATCH v2 1/2] x86/mm/64: Fix vmapped stack syncing on very-large-memory 4-level systems Andy Lutomirski
2018-01-25 21:49   ` Dave Hansen
2018-01-25 22:00     ` Andy Lutomirski
2018-01-26  9:30       ` Ingo Molnar
2018-01-26 18:54       ` Kirill A. Shutemov
2018-01-26 15:06   ` [tip:x86/urgent] " tip-bot for Andy Lutomirski
2018-01-26 18:51   ` [PATCH v2 1/2] " Kirill A. Shutemov
2018-01-26 19:02     ` Andy Lutomirski [this message]
2018-01-26 20:50       ` Kirill A. Shutemov
2018-01-25 21:12 ` [PATCH v2 2/2] x86/mm/64: Tighten up vmalloc_fault() sanity checks on 5-level kernels Andy Lutomirski
2018-01-26 15:07   ` [tip:x86/urgent] " tip-bot for Andy Lutomirski

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=CALCETrUaHysYacCF1t_Sap0jHhqBUb7dUKjaVDtPyM-kUMR3sw@mail.gmail.com \
    --to=luto@kernel.org \
    --cc=bp@alien8.de \
    --cc=dave.hansen@intel.com \
    --cc=khlebnikov@yandex-team.ru \
    --cc=kirill@shutemov.name \
    --cc=linux-kernel@vger.kernel.org \
    --cc=neil.berrington@datacore.com \
    --cc=stable@vger.kernel.org \
    --cc=x86@kernel.org \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

LKML Archive on lore.kernel.org

Archives are clonable:
	git clone --mirror https://lore.kernel.org/lkml/0 lkml/git/0.git
	git clone --mirror https://lore.kernel.org/lkml/1 lkml/git/1.git
	git clone --mirror https://lore.kernel.org/lkml/2 lkml/git/2.git
	git clone --mirror https://lore.kernel.org/lkml/3 lkml/git/3.git
	git clone --mirror https://lore.kernel.org/lkml/4 lkml/git/4.git
	git clone --mirror https://lore.kernel.org/lkml/5 lkml/git/5.git
	git clone --mirror https://lore.kernel.org/lkml/6 lkml/git/6.git
	git clone --mirror https://lore.kernel.org/lkml/7 lkml/git/7.git
	git clone --mirror https://lore.kernel.org/lkml/8 lkml/git/8.git
	git clone --mirror https://lore.kernel.org/lkml/9 lkml/git/9.git

	# If you have public-inbox 1.1+ installed, you may
	# initialize and index your mirror using the following commands:
	public-inbox-init -V2 lkml lkml/ https://lore.kernel.org/lkml \
		linux-kernel@vger.kernel.org
	public-inbox-index lkml

Example config snippet for mirrors

Newsgroup available over NNTP:
	nntp://nntp.lore.kernel.org/org.kernel.vger.linux-kernel


AGPL code for this site: git clone https://public-inbox.org/public-inbox.git