From: Dave Hansen <dave.hansen@intel.com>
To: Valentin Schneider <vschneid@redhat.com>,
Steven Rostedt <rostedt@goodmis.org>
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Subject: Re: [PATCH v5 00/25] context_tracking,x86: Defer some IPIs until a user->kernel transition
Date: Fri, 2 May 2025 10:57:00 -0700 [thread overview]
Message-ID: <2c5d11cf-ad06-444c-b84a-42de7a10159d@intel.com> (raw)
In-Reply-To: <xhsmho6wb9de3.mognet@vschneid-thinkpadt14sgen2i.remote.csb>
gah, the cc list here is rotund...
On 5/2/25 09:38, Valentin Schneider wrote:
...
>> All of the paths to enter the kernel from userspace have some
>> SWITCH_TO_KERNEL_CR3 variant. If they didn't, the userspace that they
>> entered from could have attacked the kernel with Meltdown.
>>
>> I'm theorizing that if this is _just_ about avoiding TLB flush IPIs that
>> you can get away with a single mechanism.
>
> So right now there would indeed be the TLB flush IPIs, but also the
> text_poke() ones (sync_core() after patching text).
>
> These are the two NOHZ-breaking IPIs that show up on my HP box, and that I
> also got reports for from folks using NOHZ_FULL + CPU isolation in
> production, mostly on SPR "edge enhanced" type of systems.
...
> While I don't expect the list to grow much, it's unfortunately not just the
> TLB flush IPIs.
Isn't text patching way easier than TLB flushes? You just need *some*
serialization. Heck, since TLB flushes are architecturally serializing,
you could probably even reuse the exact same mechanism: implement
deferred text patch serialization operations as a deferred TLB flush.
The hardest part is figuring out which CPUs are in the state where they
can be deferred or not. But you have to solve that in any case, and you
already have an algorithm to do it.
next prev parent reply other threads:[~2025-05-02 17:57 UTC|newest]
Thread overview: 41+ messages / expand[flat|nested] mbox.gz Atom feed top
2025-04-29 11:32 [PATCH v5 00/25] context_tracking,x86: Defer some IPIs until a user->kernel transition Valentin Schneider
2025-04-29 11:32 ` [PATCH v5 01/25] objtool: Make validate_call() recognize indirect calls to pv_ops[] Valentin Schneider
2025-04-29 11:32 ` [PATCH v5 02/25] objtool: Flesh out warning related to pv_ops[] calls Valentin Schneider
2025-04-29 11:32 ` [PATCH v5 03/25] rcu: Add a small-width RCU watching counter debug option Valentin Schneider
2025-04-29 11:32 ` [PATCH v5 04/25] rcutorture: Make TREE04 use CONFIG_RCU_DYNTICKS_TORTURE Valentin Schneider
2025-04-29 11:32 ` [PATCH v5 05/25] jump_label: Add annotations for validating noinstr usage Valentin Schneider
2025-04-29 11:32 ` [PATCH v5 06/25] static_call: Add read-only-after-init static calls Valentin Schneider
2025-04-29 11:32 ` [PATCH v5 07/25] x86/paravirt: Mark pv_sched_clock static call as __ro_after_init Valentin Schneider
2025-04-29 11:32 ` [PATCH v5 08/25] x86/idle: Mark x86_idle " Valentin Schneider
2025-04-29 11:32 ` [PATCH v5 09/25] x86/paravirt: Mark pv_steal_clock " Valentin Schneider
2025-04-29 11:32 ` [PATCH v5 10/25] riscv/paravirt: " Valentin Schneider
2025-04-29 11:32 ` [PATCH v5 11/25] loongarch/paravirt: " Valentin Schneider
2025-04-29 11:32 ` [PATCH v5 12/25] arm64/paravirt: " Valentin Schneider
2025-04-29 11:32 ` [PATCH v5 13/25] arm/paravirt: " Valentin Schneider
2025-04-29 11:32 ` [PATCH v5 14/25] perf/x86/amd: Mark perf_lopwr_cb " Valentin Schneider
2025-04-29 11:32 ` [PATCH v5 15/25] sched/clock: Mark sched_clock_running key " Valentin Schneider
2025-04-29 11:32 ` [PATCH v5 16/25] KVM: VMX: Mark __kvm_is_using_evmcs static " Valentin Schneider
2025-04-29 11:32 ` [PATCH v5 17/25] x86/speculation/mds: Mark mds_idle_clear key as allowed in .noinstr Valentin Schneider
2025-04-29 11:32 ` [PATCH v5 18/25] sched/clock, x86: Mark __sched_clock_stable " Valentin Schneider
2025-04-29 11:32 ` [PATCH v5 19/25] KVM: VMX: Mark vmx_l1d_should flush and vmx_l1d_flush_cond keys " Valentin Schneider
2025-04-29 11:32 ` [PATCH v5 20/25] stackleack: Mark stack_erasing_bypass key " Valentin Schneider
2025-04-29 11:32 ` [PATCH v5 21/25] objtool: Add noinstr validation for static branches/calls Valentin Schneider
2025-04-29 11:32 ` [PATCH v5 22/25] module: Remove outdated comment about text_size Valentin Schneider
2025-05-05 14:27 ` Petr Pavlu
2025-04-29 11:32 ` [PATCH v5 23/25] module: Add MOD_NOINSTR_TEXT mem_type Valentin Schneider
2025-04-29 11:32 ` [PATCH v5 24/25] context-tracking: Introduce work deferral infrastructure Valentin Schneider
2025-04-29 11:32 ` [PATCH v5 25/25] context_tracking,x86: Defer kernel text patching IPIs Valentin Schneider
2025-04-29 16:11 ` [PATCH v5 00/25] context_tracking,x86: Defer some IPIs until a user->kernel transition Dave Hansen
2025-04-30 17:20 ` Steven Rostedt
2025-04-30 18:07 ` Dave Hansen
2025-04-30 19:42 ` Steven Rostedt
2025-04-30 20:00 ` Dave Hansen
2025-05-02 9:55 ` Valentin Schneider
2025-05-02 13:53 ` Dave Hansen
2025-05-02 16:38 ` Valentin Schneider
2025-05-02 17:57 ` Dave Hansen [this message]
2025-05-05 15:45 ` Valentin Schneider
2025-05-02 11:22 ` Peter Zijlstra
2025-05-02 14:33 ` Dave Hansen
2025-05-02 15:20 ` Peter Zijlstra
2025-05-02 16:36 ` x86 RAR implementation Dave Hansen
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