From: Peter Zijlstra <peterz@infradead.org>
To: "Kirill A. Shutemov" <kirill@shutemov.name>
Cc: Bharata B Rao <bharata@amd.com>,
ananth.narayan@amd.com,
"Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
Dave Hansen <dave.hansen@linux.intel.com>,
Andy Lutomirski <luto@kernel.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>,
Taras Madan <tarasmadan@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: [PATCHv8 00/11] Linear Address Masking enabling
Date: Mon, 5 Sep 2022 16:30:25 +0200 [thread overview]
Message-ID: <YxYIAVx2qJLMDJlC@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <20220905134457.a2f7uluq42frsgwe@box.shutemov.name>
On Mon, Sep 05, 2022 at 04:44:57PM +0300, Kirill A. Shutemov wrote:
> On Mon, Sep 05, 2022 at 10:35:44AM +0530, Bharata B Rao wrote:
> > Hi Kirill,
> >
> > On 9/4/2022 6:30 AM, Kirill A. Shutemov wrote:
> > > On Tue, Aug 30, 2022 at 04:00:53AM +0300, Kirill A. Shutemov wrote:
> > >> Linear Address Masking[1] (LAM) modifies the checking that is applied to
> > >> 64-bit linear addresses, allowing software to use of the untranslated
> > >> address bits for metadata.
> > >>
> > >> The patchset brings support for LAM for userspace addresses. Only LAM_U57 at
> > >> this time.
> > >>
> > >> Please review and consider applying.
> > >>
> > >> git://git.kernel.org/pub/scm/linux/kernel/git/kas/linux.git lam
> > >
> > > +Bharata, Ananth.
> > >
> > > Do you folks have any feedback on the patchset?
> > >
> > > Looks like AMD version of the tagged pointers feature does not get
> > > traction as of now, but I want to be sure that the interface introduced
> > > here can be suitable for your future plans.
> > >
> > > Do you see anything in the interface that can prevent it to be extended to
> > > the AMD feature?
> >
> > The arch_prctl() extensions is generic enough that it should be good.
> >
> > The untagged_addr() macro looks like this from one of the callers:
> >
> > start = untagged_addr(mm, start);
> > ffffffff814d39bb: 48 8b 8d 40 ff ff ff mov -0xc0(%rbp),%rcx
> > ffffffff814d39c2: 48 89 f2 mov %rsi,%rdx
> > ffffffff814d39c5: 48 c1 fa 3f sar $0x3f,%rdx
> > ffffffff814d39c9: 48 0b 91 50 03 00 00 or 0x350(%rcx),%rdx
> > ffffffff814d39d0: 48 21 f2 and %rsi,%rdx
> > ffffffff814d39d3: 49 89 d6 mov %rdx,%r14
> >
> > Can this overhead of a few additional instructions be removed for
> > platforms that don't have LAM feature? I haven't measured how much
> > overhead this effectively contributes to in real, but wonder if it is
> > worth optimizing for non-LAM platforms.
>
> I'm not sure how the optimization should look like. I guess we can stick
> static_cpu_has() there, but I'm not convinced that adding jumps there will
> be beneficial.
I suppose the critical bit is the memory load. That can stall and then
you're sad. A jump_label is easy enough to add.
next prev parent reply other threads:[~2022-09-05 14:30 UTC|newest]
Thread overview: 67+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-08-30 1:00 Kirill A. Shutemov
2022-08-30 1:00 ` [PATCHv8 01/11] x86/mm: Fix CR3_ADDR_MASK Kirill A. Shutemov
2022-08-30 1:00 ` [PATCHv8 02/11] x86: CPUID and CR3/CR4 flags for Linear Address Masking Kirill A. Shutemov
2022-08-30 1:00 ` [PATCHv8 03/11] mm: Pass down mm_struct to untagged_addr() Kirill A. Shutemov
2022-08-30 1:00 ` [PATCHv8 04/11] x86/mm: Handle LAM on context switch Kirill A. Shutemov
2022-08-30 1:00 ` [PATCHv8 05/11] x86/uaccess: Provide untagged_addr() and remove tags before address check Kirill A. Shutemov
2022-08-30 1:00 ` [PATCHv8 06/11] x86/mm: Provide arch_prctl() interface for LAM Kirill A. Shutemov
2022-08-30 1:01 ` [PATCHv8 07/11] x86: Expose untagging mask in /proc/$PID/arch_status Kirill A. Shutemov
2022-08-30 1:01 ` [PATCHv8 08/11] selftests/x86/lam: Add malloc and tag-bits test cases for linear-address masking Kirill A. Shutemov
2022-08-30 1:01 ` [PATCHv8 09/11] selftests/x86/lam: Add mmap and SYSCALL " Kirill A. Shutemov
2022-09-07 3:19 ` Robert Hoo
2022-09-09 11:24 ` Zhang, Weihong
2022-08-30 1:01 ` [PATCHv8 10/11] selftests/x86/lam: Add io_uring " Kirill A. Shutemov
2022-08-30 1:01 ` [PATCHv8 11/11] selftests/x86/lam: Add inherit " Kirill A. Shutemov
2022-09-01 17:45 ` [PATCHv8 00/11] Linear Address Masking enabling Ashok Raj
2022-09-04 0:39 ` Kirill A. Shutemov
2022-09-09 16:08 ` Ashok Raj
2022-09-12 20:39 ` Jacob Pan
2022-09-12 21:41 ` Dave Hansen
2022-09-12 22:55 ` Jacob Pan
2022-09-13 0:06 ` Kirill A. Shutemov
2022-09-13 0:23 ` Ashok Raj
2022-09-12 22:49 ` Kirill A. Shutemov
2022-09-13 0:08 ` Jacob Pan
2022-09-13 0:18 ` Kirill A. Shutemov
2022-09-14 14:45 ` Kirill A. Shutemov
2022-09-14 15:11 ` Ashok Raj
2022-09-14 15:18 ` Kirill A. Shutemov
2022-09-14 15:31 ` Ashok Raj
2022-09-14 15:45 ` Kirill A. Shutemov
2022-09-14 23:51 ` Jacob Pan
2022-09-15 9:01 ` Kirill A. Shutemov
2022-09-15 17:28 ` Kirill A. Shutemov
2022-09-20 13:14 ` Jason Gunthorpe
2022-09-20 14:57 ` Ashok Raj
2022-09-20 16:06 ` Dave Hansen
2022-09-20 16:27 ` Jason Gunthorpe
2022-09-20 18:41 ` Jacob Pan
2022-09-20 18:50 ` Jason Gunthorpe
2022-09-20 20:44 ` Jacob Pan
2022-09-21 0:01 ` Jason Gunthorpe
2022-09-21 9:36 ` Tian, Kevin
2022-09-21 16:57 ` Dave Hansen
2022-09-21 17:08 ` Ashok Raj
2022-09-21 17:11 ` Dave Hansen
2022-09-21 17:29 ` Ashok Raj
2022-09-21 18:11 ` Jason Gunthorpe
2022-09-23 0:42 ` Kirill A. Shutemov
2022-09-23 5:27 ` Ashok Raj
2022-09-23 9:38 ` Kirill A. Shutemov
2022-09-23 11:46 ` Jason Gunthorpe
2022-09-23 14:18 ` Dave Hansen
2022-09-23 14:42 ` Jason Gunthorpe
2022-09-23 14:59 ` Ashok Raj
2022-09-23 15:28 ` Ashok Raj
2022-09-23 15:31 ` Dave Hansen
2022-09-23 15:44 ` Ashok Raj
2022-09-23 16:23 ` Dave Hansen
2022-09-23 16:44 ` Jason Gunthorpe
2022-09-04 1:00 ` Kirill A. Shutemov
2022-09-05 5:05 ` Bharata B Rao
2022-09-05 13:44 ` Kirill A. Shutemov
2022-09-05 14:30 ` Peter Zijlstra [this message]
2022-09-05 15:35 ` Kirill A. Shutemov
2022-09-05 15:46 ` Peter Zijlstra
2022-09-05 16:47 ` Kirill A. Shutemov
2022-09-06 8:39 ` Peter Zijlstra
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