linux-kernel - Re: [RFC PATCH v3 13/15] context_tracking,x86: Add infrastructure to defer kernel TLBI

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <xhsmh1pyh6p0k.mognet@vschneid-thinkpadt14sgen2i.remote.csb>
Date: Mon, 09 Dec 2024 13:04:43 +0100
From: Valentin Schneider <vschneid@...hat.com>
To: Petr Tesarik <ptesarik@...e.com>, Peter Zijlstra <peterz@...radead.org>
Cc: Dave Hansen <dave.hansen@...el.com>, linux-kernel@...r.kernel.org,
 linux-doc@...r.kernel.org, kvm@...r.kernel.org, linux-mm@...ck.org,
 bpf@...r.kernel.org, x86@...nel.org, rcu@...r.kernel.org,
 linux-kselftest@...r.kernel.org, Steven Rostedt <rostedt@...dmis.org>,
 Masami Hiramatsu <mhiramat@...nel.org>, Jonathan Corbet <corbet@....net>,
 Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>,
 Borislav Petkov <bp@...en8.de>, Dave Hansen <dave.hansen@...ux.intel.com>,
 "H. Peter Anvin" <hpa@...or.com>, Paolo Bonzini <pbonzini@...hat.com>,
 Wanpeng Li <wanpengli@...cent.com>, Vitaly Kuznetsov
 <vkuznets@...hat.com>, Andy Lutomirski <luto@...nel.org>, Frederic
 Weisbecker <frederic@...nel.org>, "Paul E. McKenney" <paulmck@...nel.org>,
 Neeraj
 Upadhyay <quic_neeraju@...cinc.com>, Joel Fernandes
 <joel@...lfernandes.org>, Josh Triplett <josh@...htriplett.org>, Boqun
 Feng <boqun.feng@...il.com>, Mathieu Desnoyers
 <mathieu.desnoyers@...icios.com>, Lai Jiangshan <jiangshanlai@...il.com>,
 Zqiang <qiang.zhang1211@...il.com>, Andrew Morton
 <akpm@...ux-foundation.org>, Uladzislau Rezki <urezki@...il.com>,
 Christoph Hellwig <hch@...radead.org>, Lorenzo Stoakes
 <lstoakes@...il.com>, Josh Poimboeuf <jpoimboe@...nel.org>, Jason Baron
 <jbaron@...mai.com>, Kees Cook <keescook@...omium.org>, Sami Tolvanen
 <samitolvanen@...gle.com>, Ard Biesheuvel <ardb@...nel.org>, Nicholas
 Piggin <npiggin@...il.com>, Juerg Haefliger
 <juerg.haefliger@...onical.com>, Nicolas Saenz Julienne
 <nsaenz@...nel.org>, "Kirill A. Shutemov"
 <kirill.shutemov@...ux.intel.com>, Nadav Amit <namit@...are.com>, Dan
 Carpenter <error27@...il.com>, Chuang Wang <nashuiliang@...il.com>, Yang
 Jihong <yangjihong1@...wei.com>, Petr Mladek <pmladek@...e.com>, "Jason A.
 Donenfeld" <Jason@...c4.com>, Song Liu <song@...nel.org>, Julian Pidancet
 <julian.pidancet@...cle.com>, Tom Lendacky <thomas.lendacky@....com>,
 Dionna Glaze <dionnaglaze@...gle.com>, Thomas Weißschuh
 <linux@...ssschuh.net>, Juri Lelli <juri.lelli@...hat.com>, Marcelo
 Tosatti <mtosatti@...hat.com>, Yair Podemsky <ypodemsk@...hat.com>, Daniel
 Wagner <dwagner@...e.de>
Subject: Re: [RFC PATCH v3 13/15] context_tracking,x86: Add infrastructure
 to defer kernel TLBI

On 05/12/24 18:31, Petr Tesarik wrote:
> On Thu, 21 Nov 2024 16:30:16 +0100
> Peter Zijlstra <peterz@...radead.org> wrote:
>
>> On Thu, Nov 21, 2024 at 07:07:44AM -0800, Dave Hansen wrote:
>> > On 11/21/24 03:12, Peter Zijlstra wrote:
>> > >> I see e.g. ds_clear_cea() clears PTEs that can have the _PAGE_GLOBAL flag,
>> > >> and it correctly uses the non-deferrable flush_tlb_kernel_range().
>> > >
>> > > I always forget what we use global pages for, dhansen might know, but
>> > > let me try and have a look.
>> > >
>> > > I *think* we only have GLOBAL on kernel text, and that only sometimes.
>> >
>> > I think you're remembering how _PAGE_GLOBAL gets used when KPTI is in play.
>>
>> Yah, I suppose I am. That was the last time I had a good look at this
>> stuff :-)
>>
>> > Ignoring KPTI for a sec... We use _PAGE_GLOBAL for all kernel mappings.
>> > Before PCIDs, global mappings let the kernel TLB entries live across CR3
>> > writes. When PCIDs are in play, global mappings let two different ASIDs
>> > share TLB entries.
>>
>> Hurmph.. bah. That means we do need that horrible CR4 dance :/
>
> In general, yes.
>
> But I wonder what exactly was the original scenario encountered by
> Valentin. I mean, if TLB entry invalidations were necessary to sync
> changes to kernel text after flipping a static branch, then it might be
> less overhead to make a list of affected pages and call INVLPG on them.
>
> AFAIK there is currently no such IPI function for doing that, but if we
> could add one. If the list of invalidated global pages is reasonably
> short, of course.
>
> Valentin, do you happen to know?
>

So from my experimentation (hackbench + kernel compilation on housekeeping
CPUs, dummy while(1) userspace loop on isolated CPUs), the TLB flushes only
occurred from vunmap() - mainly from all the hackbench threads coming and
going.

Static branch updates only seem to trigger the sync_core() IPI, at least on
x86.

> Petr T