linux-kernel - Re: [PATCH 1/6] arm64/vdso: use the fault callback to map vvar pages

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Date:   Fri, 24 Jul 2020 18:26:23 +0100
From:   Catalin Marinas <catalin.marinas@....com>
To:     Andrei Vagin <avagin@...il.com>, Will Deacon <will@...nel.org>,
        Mark Rutland <mark.rutland@....com>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Christian Brauner <christian.brauner@...ntu.com>,
        Vincenzo Frascino <vincenzo.frascino@....com>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        Dmitry Safonov <dima@...sta.com>
Subject: Re: [PATCH 1/6] arm64/vdso: use the fault callback to map vvar pages

On Wed, 24 Jun 2020 01:33:16 -0700, Andrei Vagin wrote:
> Currently the vdso has no awareness of time namespaces, which may
> apply distinct offsets to processes in different namespaces. To handle
> this within the vdso, we'll need to expose a per-namespace data page.
> 
> As a preparatory step, this patch separates the vdso data page from
> the code pages, and has it faulted in via its own fault callback.
> Subsquent patches will extend this to support distinct pages per time
> namespace.
> 
> [...]

Applied to arm64 (for-next/timens), provisionally.

One potential issue I did not check is the compat vDSO. The arm32 port
does not support timens currently. IIUC, with these patches and
COMPAT_VDSO enabled, it will allow timens for compat processes. Normally
I'd like the arm32 support first before updating compat but I don't
think there would be any interface incompatibility here.

However, does this still work for arm32 processes if COMPAT_VDSO is
disabled in the arm64 kernel?

[1/6] arm64/vdso: use the fault callback to map vvar pages
      https://git.kernel.org/arm64/c/d53b5c013e1e
[2/6] arm64/vdso: Zap vvar pages when switching to a time namespace
      https://git.kernel.org/arm64/c/1b6867d2916b
[3/6] arm64/vdso: Add time namespace page
      https://git.kernel.org/arm64/c/3503d56cc723
[4/6] arm64/vdso: Handle faults on timens page
      https://git.kernel.org/arm64/c/ee3cda8e4606
[5/6] arm64/vdso: Restrict splitting VVAR VMA
      https://git.kernel.org/arm64/c/bcf996434240
[6/6] arm64: enable time namespace support
      https://git.kernel.org/arm64/c/9614cc576d76

Thanks!

-- 
Catalin