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Subject: Re: [PATCH] x86/mm/pat: Fix missing preemption disable for __native_flush_tlb()
From:   Andy Lutomirski <luto@amacapital.net>
In-Reply-To: <154180834787.2060925.7738215365584115230.stgit@dwillia2-desk3.amr.corp.intel.com>
Date:   Fri, 9 Nov 2018 16:22:15 -0800
Cc:     tglx@linutronix.de,
        Sebastian Andrzej Siewior <bigeasy@linutronix.de>,
        Andy Lutomirski <luto@kernel.org>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Borislav Petkov <bp@alien8.de>, stable@vger.kernel.org,
        x86@kernel.org, linux-kernel@vger.kernel.org
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Message-Id: <7590EF40-B0CF-40BD-9D29-FB731A2A2E3A@amacapital.net>
References: <154180834787.2060925.7738215365584115230.stgit@dwillia2-desk3.amr.corp.intel.com>
To:     Dan Williams <dan.j.williams@intel.com>
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk


> On Nov 9, 2018, at 4:05 PM, Dan Williams <dan.j.williams@intel.com> wrote:=

>=20
> Commit f77084d96355 "x86/mm/pat: Disable preemption around
> __flush_tlb_all()" addressed a case where __flush_tlb_all() is called
> without preemption being disabled. It also left a warning to catch other
> cases where preemption is not disabled. That warning triggers for the
> memory hotplug path which is also used for persistent memory enabling:

I don=E2=80=99t think I agree with the patch. If you call __flush_tlb_all() i=
n a context where you might be *migrated*, then there=E2=80=99s a bug. We co=
uld change the code to allow this particular use by checking that we haven=E2=
=80=99t done SMP init yet, perhaps.

>=20
> WARNING: CPU: 35 PID: 911 at ./arch/x86/include/asm/tlbflush.h:460
> RIP: 0010:__flush_tlb_all+0x1b/0x3a
> [..]
> Call Trace:
>  phys_pud_init+0x29c/0x2bb
>  kernel_physical_mapping_init+0xfc/0x219
>  init_memory_mapping+0x1a5/0x3b0
>  arch_add_memory+0x2c/0x50
>  devm_memremap_pages+0x3aa/0x610
>  pmem_attach_disk+0x585/0x700 [nd_pmem]
>=20
> Rather than audit all __flush_tlb_all() callers to add preemption, just
> do it internally to __flush_tlb_all().
>=20
> Fixes: f77084d96355 ("x86/mm/pat: Disable preemption around __flush_tlb_al=
l()")
> Cc: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
> Cc: Thomas Gleixner <tglx@linutronix.de>
> Cc: Andy Lutomirski <luto@kernel.org>
> Cc: Dave Hansen <dave.hansen@linux.intel.com>
> Cc: Peter Zijlstra <peterz@infradead.org>
> Cc: Borislav Petkov <bp@alien8.de>
> Cc: <stable@vger.kernel.org>
> Signed-off-by: Dan Williams <dan.j.williams@intel.com>
> ---
> arch/x86/include/asm/tlbflush.h |    8 ++++----
> arch/x86/mm/pageattr.c          |    6 +-----
> 2 files changed, 5 insertions(+), 9 deletions(-)
>=20
> diff --git a/arch/x86/include/asm/tlbflush.h b/arch/x86/include/asm/tlbflu=
sh.h
> index d760611cfc35..049e0aca0fb5 100644
> --- a/arch/x86/include/asm/tlbflush.h
> +++ b/arch/x86/include/asm/tlbflush.h
> @@ -454,11 +454,10 @@ static inline void __native_flush_tlb_one_user(unsig=
ned long addr)
> static inline void __flush_tlb_all(void)
> {
>    /*
> -     * This is to catch users with enabled preemption and the PGE feature=

> -     * and don't trigger the warning in __native_flush_tlb().
> +     *  Preemption needs to be disabled around __flush_tlb* calls
> +     *  due to CR3 reload in __native_flush_tlb().
>     */
> -    VM_WARN_ON_ONCE(preemptible());
> -
> +    preempt_disable();
>    if (boot_cpu_has(X86_FEATURE_PGE)) {
>        __flush_tlb_global();
>    } else {
> @@ -467,6 +466,7 @@ static inline void __flush_tlb_all(void)
>         */
>        __flush_tlb();
>    }
> +    preempt_enable();
> }
>=20
> /*
> diff --git a/arch/x86/mm/pageattr.c b/arch/x86/mm/pageattr.c
> index db7a10082238..f799076e3d57 100644
> --- a/arch/x86/mm/pageattr.c
> +++ b/arch/x86/mm/pageattr.c
> @@ -2309,13 +2309,9 @@ void __kernel_map_pages(struct page *page, int nump=
ages, int enable)
>=20
>    /*
>     * We should perform an IPI and flush all tlbs,
> -     * but that can deadlock->flush only current cpu.
> -     * Preemption needs to be disabled around __flush_tlb_all() due to
> -     * CR3 reload in __native_flush_tlb().
> +     * but that can deadlock->flush only current cpu:
>     */
> -    preempt_disable();
>    __flush_tlb_all();
> -    preempt_enable();
>=20
>    arch_flush_lazy_mmu_mode();
> }
>=20