linux-kernel - Re: Flushing user entries for kernel mappings in x86

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Message-ID: <CALCETrWy3v-DiCNJs=wkym_q4U07-mtmEqy1YgMvAJ8AOT8MJQ@mail.gmail.com>
Date:   Tue, 28 Aug 2018 20:45:01 -0700
From:   Andy Lutomirski <luto@...nel.org>
To:     Nadav Amit <nadav.amit@...il.com>
Cc:     Andy Lutomirski <luto@...nel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: Flushing user entries for kernel mappings in x86

On Tue, Aug 28, 2018 at 6:46 PM, Nadav Amit <nadav.amit@...il.com> wrote:
> Hello Andy,
>
> 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 ].

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.