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From: Nadav Amit <namit@vmware.com>
To: Jann Horn <jannh@google.com>
Cc: Peter Zijlstra <peterz@infradead.org>,
	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>,
	the arch/x86 maintainers <x86@kernel.org>,
	LKML <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 20:04:19 +0000	[thread overview]
Message-ID: <6331796E-8925-4426-A0A6-5CB342178202@vmware.com> (raw)
In-Reply-To: <CAG48ez1LxU_swf30Ndj=vjZLeSKg83Oi4f2Kd+wSUygPXA0cGg@mail.gmail.com>

> On May 31, 2019, at 12:20 PM, Jann Horn <jannh@google.com> wrote:
> 
> On Fri, May 31, 2019 at 8:29 PM Nadav Amit <namit@vmware.com> wrote:
>> [ +Jann Horn ]
>> 
>>> On May 31, 2019, at 3:57 AM, Peter Zijlstra <peterz@infradead.org> wrote:
>>> 
>>> 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.
> [...]
>> A #MC might be caused. I tried to avoid it by not allowing freeing of
>> page-tables in such way. Did I miss something else? Some interaction with
>> MTRR changes? I’ll think about it some more, but I don’t see how.
> 
> I don't really know much about this topic, but here's a random comment
> since you cc'ed me: If the physical memory range was freed and
> reallocated, could you end up with speculatively executed cached
> memory reads from I/O memory? (And if so, would that be bad?)

Thanks. I thought that your experience with TLB page-freeing bugs may
be valuable, and you frequently find my mistakes. ;-)

Yes, speculatively executed cached reads from the I/O memory are a concern.
IIRC they caused #MC on AMD. If page-tables are not changes, but only PTEs
are changed, I don’t see how it can be a problem. I also looked at the MTRR
setting code, but I don’t see a concrete problem.


  reply	other threads:[~2019-05-31 20:04 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
2019-05-31 18:29     ` Nadav Amit
2019-05-31 19:20       ` Jann Horn
2019-05-31 20:04         ` Nadav Amit [this message]
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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