linux-kernel - Re: [RFC 07/20] mm: move x86 tlb

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Message-ID: <CALCETrV488g=U6dK5XfhczCUfn3Wvgs6kF8fvdBSZ5DfTwR+RQ@mail.gmail.com>
Date:   Sun, 31 Jan 2021 10:26:34 -0800
From:   Andy Lutomirski <luto@...nel.org>
To:     Nadav Amit <nadav.amit@...il.com>
Cc:     Linux-MM <linux-mm@...ck.org>, LKML <linux-kernel@...r.kernel.org>,
        Nadav Amit <namit@...are.com>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Andy Lutomirski <luto@...nel.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Will Deacon <will@...nel.org>, Yu Zhao <yuzhao@...gle.com>,
        Nick Piggin <npiggin@...il.com>, X86 ML <x86@...nel.org>
Subject: Re: [RFC 07/20] mm: move x86 tlb_gen to generic code

On Sat, Jan 30, 2021 at 4:16 PM Nadav Amit <nadav.amit@...il.com> wrote:
>
> From: Nadav Amit <namit@...are.com>
>
> x86 currently has a TLB-generation tracking logic that can be used by
> additional architectures (as long as they implement some additional
> logic).
>
> Extract the relevant pieces of code from x86 to general TLB code. This
> would be useful to allow to write the next "fine granularity deferred
> TLB flushes detection" patches without making them x86-specific.

Tentative ACK.

My biggest concern about this is that, once it's exposed to core code,
people might come up with clever-but-incorrect ways to abuse it.  Oh
well.

>  struct workqueue_struct *efi_rts_wq;
> diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
> index 0974ad501a47..2035ac319c2b 100644
> --- a/include/linux/mm_types.h
> +++ b/include/linux/mm_types.h
> @@ -560,6 +560,17 @@ struct mm_struct {
>
>  #ifdef CONFIG_IOMMU_SUPPORT
>                 u32 pasid;
> +#endif
> +#ifdef CONFIG_ARCH_HAS_TLB_GENERATIONS
> +               /*
> +                * Any code that needs to do any sort of TLB flushing for this
> +                * mm will first make its changes to the page tables, then
> +                * increment tlb_gen, then flush.  This lets the low-level
> +                * flushing code keep track of what needs flushing.
> +                *
> +                * This is not used on Xen PV.

That last comment should probably go away.