From: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
To: Michal Hocko <mhocko@suse.com>
Cc: Dave Hansen <dave.hansen@linux.intel.com>,
Andy Lutomirski <luto@kernel.org>,
Peter Zijlstra <peterz@infradead.org>,
x86@kernel.org, Kostya Serebryany <kcc@google.com>,
Andrey Ryabinin <ryabinin.a.a@gmail.com>,
Andrey Konovalov <andreyknvl@gmail.com>,
Alexander Potapenko <glider@google.com>,
Dmitry Vyukov <dvyukov@google.com>,
"H . J . Lu" <hjl.tools@gmail.com>,
Andi Kleen <ak@linux.intel.com>,
Rick Edgecombe <rick.p.edgecombe@intel.com>,
linux-mm@kvack.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCHv3 6/8] x86/mm: Provide ARCH_GET_UNTAG_MASK and ARCH_ENABLE_TAGGED_ADDR
Date: Thu, 16 Jun 2022 20:05:10 +0300 [thread overview]
Message-ID: <20220616170510.gpm5pjd4yzk7hfsx@black.fi.intel.com> (raw)
In-Reply-To: <YqdM8ZIi0/35IhzF@dhcp22.suse.cz>
On Mon, Jun 13, 2022 at 04:42:57PM +0200, Michal Hocko wrote:
> On Fri 10-06-22 17:35:25, Kirill A. Shutemov wrote:
> [...]
> > diff --git a/arch/x86/kernel/process_64.c b/arch/x86/kernel/process_64.c
> > index 1962008fe743..93c8eba1a66d 100644
> > --- a/arch/x86/kernel/process_64.c
> > +++ b/arch/x86/kernel/process_64.c
> > @@ -742,6 +742,32 @@ static long prctl_map_vdso(const struct vdso_image *image, unsigned long addr)
> > }
> > #endif
> >
> > +static int prctl_enable_tagged_addr(unsigned long nr_bits)
> > +{
> > + struct mm_struct *mm = current->mm;
> > +
> > + /* Already enabled? */
> > + if (mm->context.lam_cr3_mask)
> > + return -EBUSY;
> > +
> > + /* LAM has to be enabled before spawning threads */
> > + if (get_nr_threads(current) > 1)
> > + return -EBUSY;
>
> This will not be sufficient in general. You can have mm shared with a
> process without CLONE_THREAD. So you would also need to check also
> MMF_MULTIPROCESS. But I do remember that general get_nr_threads is quite
> tricky to use properly. Make sure to CC Oleg Nesterov for more details.
>
> Also how does this work when the mm is shared with a kernel thread?
It seems we need to check mm_count to exclude kernel threads that use the
mm. But I expect it to produce bunch of false-positives.
Or we can make all CPUs to do
switch_mm(current->mm, current->mm, current);
and get LAM bits updated regardless what mm it runs. It would also remove
limitation that LAM can only be enabled when there's no threads.
But I feel that is a bad idea, but I have no clue why. :P
--
Kirill A. Shutemov
next prev parent reply other threads:[~2022-06-16 17:05 UTC|newest]
Thread overview: 67+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-06-10 14:35 [PATCHv3 0/8] Linear Address Masking enabling Kirill A. Shutemov
2022-06-10 14:35 ` [PATCHv3 1/8] x86/mm: Fix CR3_ADDR_MASK Kirill A. Shutemov
2022-06-10 23:32 ` Edgecombe, Rick P
2022-06-10 14:35 ` [PATCHv3 2/8] x86: CPUID and CR3/CR4 flags for Linear Address Masking Kirill A. Shutemov
2022-06-10 14:35 ` [PATCHv3 3/8] mm: Pass down mm_struct to untagged_addr() Kirill A. Shutemov
2022-06-10 23:33 ` Edgecombe, Rick P
2022-06-17 15:27 ` Alexander Potapenko
2022-06-17 22:38 ` Kirill A. Shutemov
2022-06-10 14:35 ` [PATCHv3 4/8] x86/mm: Handle LAM on context switch Kirill A. Shutemov
2022-06-10 23:55 ` Edgecombe, Rick P
2022-06-15 15:54 ` Kirill A. Shutemov
2022-06-16 9:08 ` Peter Zijlstra
2022-06-16 16:40 ` Kirill A. Shutemov
2022-06-17 15:35 ` Alexander Potapenko
2022-06-17 22:39 ` Kirill A. Shutemov
2022-06-28 23:33 ` Andy Lutomirski
2022-06-29 0:34 ` Kirill A. Shutemov
2022-06-30 1:51 ` Andy Lutomirski
2022-06-10 14:35 ` [PATCHv3 5/8] x86/uaccess: Provide untagged_addr() and remove tags before address check Kirill A. Shutemov
2022-06-13 17:36 ` Edgecombe, Rick P
2022-06-15 16:58 ` Kirill A. Shutemov
2022-06-15 19:06 ` Edgecombe, Rick P
2022-06-16 9:30 ` Peter Zijlstra
2022-06-16 16:44 ` Kirill A. Shutemov
2022-06-17 11:36 ` Peter Zijlstra
2022-06-17 14:22 ` H.J. Lu
2022-06-17 14:28 ` Peter Zijlstra
2022-06-16 9:34 ` Peter Zijlstra
2022-06-16 10:02 ` Peter Zijlstra
2022-06-16 16:48 ` Kirill A. Shutemov
2022-06-28 23:40 ` Andy Lutomirski
2022-06-29 0:42 ` Kirill A. Shutemov
2022-06-30 2:38 ` Andy Lutomirski
2022-07-05 0:13 ` Kirill A. Shutemov
2022-06-10 14:35 ` [PATCHv3 6/8] x86/mm: Provide ARCH_GET_UNTAG_MASK and ARCH_ENABLE_TAGGED_ADDR Kirill A. Shutemov
2022-06-10 15:25 ` Edgecombe, Rick P
2022-06-10 18:04 ` Kirill A. Shutemov
2022-06-10 16:16 ` Edgecombe, Rick P
2022-06-10 18:06 ` Kirill A. Shutemov
2022-06-10 18:08 ` Edgecombe, Rick P
2022-06-10 22:18 ` Edgecombe, Rick P
2022-06-11 1:12 ` Kirill A. Shutemov
2022-06-11 2:36 ` Edgecombe, Rick P
2022-06-12 21:03 ` Andy Lutomirski
2022-06-16 9:44 ` Peter Zijlstra
2022-06-16 16:54 ` Kirill A. Shutemov
2022-06-30 2:04 ` Andy Lutomirski
2022-06-13 14:42 ` Michal Hocko
2022-06-16 17:05 ` Kirill A. Shutemov [this message]
2022-06-19 23:40 ` Kirill A. Shutemov
2022-06-16 9:39 ` Peter Zijlstra
2022-06-28 23:42 ` Andy Lutomirski
2022-06-29 0:53 ` Kirill A. Shutemov
2022-06-30 2:29 ` Andy Lutomirski
2022-07-01 15:38 ` Kirill A. Shutemov
2022-07-02 23:55 ` Andy Lutomirski
2022-07-04 13:43 ` Kirill A. Shutemov
2022-06-10 14:35 ` [PATCHv3 7/8] x86: Expose untagging mask in /proc/$PID/arch_status Kirill A. Shutemov
2022-06-10 15:24 ` Dave Hansen
2022-06-11 1:28 ` Kirill A. Shutemov
2022-06-27 12:00 ` Catalin Marinas
2022-06-10 14:35 ` [PATCHv3 OPTIONAL 8/8] x86/mm: Extend LAM to support to LAM_U48 Kirill A. Shutemov
2022-06-16 10:00 ` Peter Zijlstra
2022-06-10 20:22 ` [PATCHv3 0/8] Linear Address Masking enabling Kostya Serebryany
2022-06-16 22:52 ` Edgecombe, Rick P
2022-06-16 23:43 ` Kirill A. Shutemov
2022-06-16 23:48 ` Edgecombe, Rick P
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