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From: Mark Rutland <mark.rutland@arm.com>
To: Andrea Arcangeli <aarcange@redhat.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>,
	Will Deacon <will@kernel.org>, Rafael Aquini <aquini@redhat.com>,
	Mark Salter <msalter@redhat.com>,
	Jon Masters <jcm@jonmasters.org>,
	linux-kernel@vger.kernel.org, linux-mm@kvack.org,
	linux-arm-kernel@lists.infradead.org,
	Michal Hocko <mhocko@kernel.org>, QI Fuli <qi.fuli@fujitsu.com>
Subject: Re: [PATCH 3/3] arm64: tlb: skip tlbi broadcast
Date: Tue, 31 Mar 2020 10:45:11 +0100	[thread overview]
Message-ID: <20200331094034.GA1131@C02TD0UTHF1T.local> (raw)
In-Reply-To: <20200316140906.GA6220@lakrids.cambridge.arm.com>

Hi Andrea,

On Mon, Mar 16, 2020 at 02:09:07PM +0000, Mark Rutland wrote:
> AFAICT, this series relies on:
> 
> * An ISB completing prior page table walks when updating TTBR. I don't
>   believe this is necessarily the case, given how things work for an
>   EL1->EL2 transition where there can be ongoing EL1 walks.

I've had confirmation that a DSB is necessary (after the MSR and ISB) to
complete any ongoing translation table walks for the stale context.

Without a DSB, those walks can observe subsequent stores and encounter
the usual set of CONSTRAINED UNPREDICTABLE behaviours (e.g. walking into
MMIO with side-effects, continuing from amalgamted entries, etc). Those
issues are purely to do with the walk, and apply regardless of whether
the resulting translations are architecturally consumed.

> * Walks never being initiated for `inactive` contexts within the current
>   translation regime. e.g. while ASID x is installed, never starting a
>   walk for ASID y. I can imagine that the architecture may permit a form
>   of this starting with intermediate walk entries in the TLBs.

I'm still chasing this point.

Thanks,
Mark.

  reply	other threads:[~2020-03-31  9:45 UTC|newest]

Thread overview: 14+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-02-23 19:25 [PATCH 0/3] arm64: tlb: skip tlbi broadcast v2 Andrea Arcangeli
2020-02-23 19:25 ` [PATCH 1/3] mm: use_mm: fix for arches checking mm_users to optimize TLB flushes Andrea Arcangeli
2020-03-03  4:28   ` Rafael Aquini
2020-02-23 19:25 ` [PATCH 2/3] arm64: select CPUMASK_OFFSTACK if NUMA Andrea Arcangeli
2020-03-03  4:31   ` Rafael Aquini
2020-02-23 19:25 ` [PATCH 3/3] arm64: tlb: skip tlbi broadcast Andrea Arcangeli
2020-03-02 15:24   ` Rafael Aquini
2020-03-04  4:19     ` Rafael Aquini
2020-03-09 11:22   ` Catalin Marinas
2020-03-14  3:16     ` Andrea Arcangeli
2020-03-16 14:09       ` Mark Rutland
2020-03-31  9:45         ` Mark Rutland [this message]
2020-04-01  0:32           ` Andrea Arcangeli
2020-03-18  8:53 ` [PATCH 0/3] arm64: tlb: skip tlbi broadcast v2 qi.fuli

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