From: Peter Zijlstra <peterz@infradead.org>
To: Nadav Amit <namit@vmware.com>
Cc: Andy Lutomirski <luto@kernel.org>, Borislav Petkov <bp@alien8.de>,
Dave Hansen <dave.hansen@intel.com>,
Ingo Molnar <mingo@redhat.com>,
Thomas Gleixner <tglx@linutronix.de>,
x86@kernel.org, linux-kernel@vger.kernel.org,
Dave Hansen <dave.hansen@linux.intel.com>
Subject: Re: [RFC PATCH v2 11/12] x86/mm/tlb: Use async and inline messages for flushing
Date: Fri, 31 May 2019 12:57:58 +0200 [thread overview]
Message-ID: <20190531105758.GO2623@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <20190531063645.4697-12-namit@vmware.com>
On Thu, May 30, 2019 at 11:36:44PM -0700, Nadav Amit wrote:
> When we flush userspace mappings, we can defer the TLB flushes, as long
> the following conditions are met:
>
> 1. No tables are freed, since otherwise speculative page walks might
> cause machine-checks.
>
> 2. No one would access userspace before flush takes place. Specifically,
> NMI handlers and kprobes would avoid accessing userspace.
>
> Use the new SMP support to execute remote function calls with inlined
> data for the matter. The function remote TLB flushing function would be
> executed asynchronously and the local CPU would continue execution as
> soon as the IPI was delivered, before the function was actually
> executed. Since tlb_flush_info is copied, there is no risk it would
> change before the TLB flush is actually executed.
>
> Change nmi_uaccess_okay() to check whether a remote TLB flush is
> currently in progress on this CPU by checking whether the asynchronously
> called function is the remote TLB flushing function. The current
> implementation disallows access in such cases, but it is also possible
> to flush the entire TLB in such case and allow access.
ARGGH, brain hurt. I'm not sure I fully understand this one. How is it
different from today, where the NMI can hit in the middle of the TLB
invalidation?
Also; since we're not waiting on the IPI, what prevents us from freeing
the user pages before the remote CPU is 'done' with them? Currently the
synchronous IPI is like a sync point where we *know* the remote CPU is
completely done accessing the page.
Where getting an IPI stops speculation, speculation again restarts
inside the interrupt handler, and until we've passed the INVLPG/MOV CR3,
speculation can happen on that TLB entry, even though we've already
freed and re-used the user-page.
Also, what happens if the TLB invalidation IPI is stuck behind another
smp_function_call IPI that is doing user-access?
As said,.. brain hurts.
next prev parent reply other threads:[~2019-05-31 10:58 UTC|newest]
Thread overview: 36+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-05-31 6:36 [RFC PATCH v2 00/12] x86: Flush remote TLBs concurrently and async Nadav Amit
2019-05-31 6:36 ` [RFC PATCH v2 01/12] smp: Remove smp_call_function() and on_each_cpu() return values Nadav Amit
2019-05-31 6:36 ` [RFC PATCH v2 02/12] smp: Run functions concurrently in smp_call_function_many() Nadav Amit
2019-05-31 6:36 ` [RFC PATCH v2 03/12] x86/mm/tlb: Refactor common code into flush_tlb_on_cpus() Nadav Amit
2019-05-31 6:36 ` [RFC PATCH v2 04/12] x86/mm/tlb: Flush remote and local TLBs concurrently Nadav Amit
2019-05-31 11:48 ` Juergen Gross
2019-05-31 19:44 ` Nadav Amit
2019-05-31 6:36 ` [RFC PATCH v2 05/12] x86/mm/tlb: Optimize local TLB flushes Nadav Amit
2019-05-31 6:36 ` [RFC PATCH v2 06/12] KVM: x86: Provide paravirtualized flush_tlb_multi() Nadav Amit
2019-05-31 6:36 ` [RFC PATCH v2 07/12] smp: Do not mark call_function_data as shared Nadav Amit
2019-05-31 10:17 ` Peter Zijlstra
2019-05-31 17:50 ` Nadav Amit
2019-05-31 6:36 ` [RFC PATCH v2 08/12] x86/tlb: Privatize cpu_tlbstate Nadav Amit
2019-05-31 18:48 ` Andy Lutomirski
2019-05-31 19:42 ` Nadav Amit
2019-05-31 6:36 ` [RFC PATCH v2 09/12] x86/apic: Use non-atomic operations when possible Nadav Amit
2019-05-31 6:36 ` [RFC PATCH v2 10/12] smp: Enable data inlining for inter-processor function call Nadav Amit
2019-05-31 6:36 ` [RFC PATCH v2 11/12] x86/mm/tlb: Use async and inline messages for flushing Nadav Amit
2019-05-31 10:57 ` Peter Zijlstra [this message]
2019-05-31 18:29 ` Nadav Amit
2019-05-31 19:20 ` Jann Horn
2019-05-31 20:04 ` Nadav Amit
2019-05-31 20:37 ` Jann Horn
2019-05-31 18:44 ` Andy Lutomirski
2019-05-31 19:31 ` Nadav Amit
2019-05-31 20:13 ` Dave Hansen
2019-05-31 20:37 ` Andy Lutomirski
2019-05-31 20:42 ` Nadav Amit
2019-05-31 21:06 ` Dave Hansen
2019-05-31 21:14 ` Andy Lutomirski
2019-05-31 21:33 ` Nadav Amit
2019-05-31 21:47 ` Andy Lutomirski
2019-05-31 22:07 ` Nadav Amit
2019-06-07 5:28 ` Nadav Amit
2019-06-07 16:42 ` Andy Lutomirski
2019-05-31 6:36 ` [RFC PATCH v2 12/12] x86/mm/tlb: Reverting the removal of flush_tlb_info from stack Nadav Amit
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