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From:   Nadav Amit <namit@vmware.com>
To:     Dave Hansen <dave.hansen@linux.intel.com>
CC:     Ingo Molnar <mingo@redhat.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Andy Lutomirski <luto@kernel.org>,
        Peter Zijlstra <peterz@infradead.org>,
        Willy Tarreau <w@1wt.eu>, "x86@kernel.org" <x86@kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH RFC v2 5/6] x86: Use global pages when PTI is disabled
Thread-Topic: [PATCH RFC v2 5/6] x86: Use global pages when PTI is disabled
Thread-Index: AQHTpnsh0/8jJ5UeL0yeIVraUEkCIaOlrnUAgAAOsAA=
Date:   Thu, 15 Feb 2018 17:47:34 +0000
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Dave Hansen <dave.hansen@linux.intel.com> wrote:

>> diff --git a/arch/x86/mm/tlb.c b/arch/x86/mm/tlb.c
>> index c67ef3fb4f35..979c7ec6baab 100644
>> --- a/arch/x86/mm/tlb.c
>> +++ b/arch/x86/mm/tlb.c
>> @@ -74,7 +74,8 @@ static void choose_new_asid(struct mm_struct *next, u6=
4 next_tlb_gen,
>> 		return;
>> 	}
>>=20
>> -	if (this_cpu_read(cpu_tlbstate.invalidate_other))
>> +	if (this_cpu_read(cpu_tlbstate.invalidate_other) &&
>> +	    !mm_pti_disable(next))
>> 		clear_asid_other();
>=20
> This isn't obviously correct.  Don't we still need to invalidate other
> user asids?

I forgot to regard this question: When you reenable PTI (after switching ba=
ck
to 64-bit process), you flush the global pages, so no kernel mappings for t=
he
32-bit process are left.

As for kernel mappings of 64-bit processes, you will flush them later, when
you switch back to 64-bit process (the indication is left set).