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From:   Jann Horn <jannh@google.com>
Date:   Fri, 2 Oct 2020 08:08:53 +0200
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Subject: Re: [PATCH v4 02/11] x86, kfence: enable KFENCE for x86
To:     Marco Elver <elver@google.com>
Cc:     Andrew Morton <akpm@linux-foundation.org>,
        Alexander Potapenko <glider@google.com>,
        "H . Peter Anvin" <hpa@zytor.com>,
        "Paul E . McKenney" <paulmck@kernel.org>,
        Andrey Konovalov <andreyknvl@google.com>,
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        Andy Lutomirski <luto@kernel.org>,
        Borislav Petkov <bp@alien8.de>,
        Catalin Marinas <catalin.marinas@arm.com>,
        Christoph Lameter <cl@linux.com>,
        Dave Hansen <dave.hansen@linux.intel.com>,
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        Dmitry Vyukov <dvyukov@google.com>,
        Eric Dumazet <edumazet@google.com>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Hillf Danton <hdanton@sina.com>,
        Ingo Molnar <mingo@redhat.com>, Jonathan.Cameron@huawei.com,
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On Tue, Sep 29, 2020 at 3:38 PM Marco Elver <elver@google.com> wrote:
> Add architecture specific implementation details for KFENCE and enable
> KFENCE for the x86 architecture. In particular, this implements the
> required interface in <asm/kfence.h> for setting up the pool and
> providing helper functions for protecting and unprotecting pages.
[...]
> diff --git a/arch/x86/include/asm/kfence.h b/arch/x86/include/asm/kfence.h
[...]
> +/* Protect the given page and flush TLBs. */
> +static inline bool kfence_protect_page(unsigned long addr, bool protect)
> +{
[...]
> +       flush_tlb_one_kernel(addr);

flush_tlb_one_kernel() -> flush_tlb_one_user() ->
__flush_tlb_one_user() -> native_flush_tlb_one_user() only flushes on
the local CPU core, not on others. If you want to leave it this way, I
think this needs a comment explaining why we're not doing a global
flush (locking context / performance overhead / ... ?).