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Subject: Re: Flushing user entries for kernel mappings in x86
From:   Nadav Amit <nadav.amit@gmail.com>
In-Reply-To: <CALCETrWy3v-DiCNJs=wkym_q4U07-mtmEqy1YgMvAJ8AOT8MJQ@mail.gmail.com>
Date:   Wed, 29 Aug 2018 01:37:55 -0700
Cc:     Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
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To:     Andy Lutomirski <luto@kernel.org>
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at 8:45 PM, Andy Lutomirski <luto@kernel.org> wrote:

> On Tue, Aug 28, 2018 at 6:46 PM, Nadav Amit <nadav.amit@gmail.com> =
wrote:
>> Hello Andy,
>>=20
>> Is there a reason for __flush_tlb_one_kernel() to flush the PTE not =
only in
>> the kernel address space, but also in the user one (as part of
>> __flush_tlb_one_user)? [ I obviously regard the case when PTI is on =
].
>=20
> In most cases, probably not, but it's fairly cheap, I think.  And it
> makes it so that we're okay if the TLB entry we're flushing is used by
> the entry code.

Thanks. I assumed that=E2=80=99s the case. I don=E2=80=99t know how =
cheap they are
(especially if INVPCID is not supported) but I guess they are not that
frequent.