From: Jann Horn <jannh@google.com>
To: Nadav Amit <namit@vmware.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 22:37:52 +0200 [thread overview]
Message-ID: <CAG48ez0pEHOskDK53LMQa=gbUSoztWR3SuAeux-aVeh_896w5Q@mail.gmail.com> (raw)
In-Reply-To: <6331796E-8925-4426-A0A6-5CB342178202@vmware.com>
On Fri, May 31, 2019 at 10:04 PM Nadav Amit <namit@vmware.com> wrote:
> > 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.
Can the *physical memory range* not be freed and assigned to another
device? Like, when you mess around with memory hotplug and PCI hotplug?
next prev parent reply other threads:[~2019-05-31 20:38 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
2019-05-31 20:37 ` Jann Horn [this message]
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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