linux-kernel - Re: [PATCH v2 13/24] drm/etnaviv: reject timeouts with tv_nsec >= NSEC_PER

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Date:   Mon, 20 Jan 2020 19:47:05 +0100
From:   Arnd Bergmann <arnd@...db.de>
To:     Lucas Stach <l.stach@...gutronix.de>
Cc:     Guido Günther <agx@...xcpu.org>,
        Philipp Zabel <p.zabel@...gutronix.de>,
        y2038 Mailman List <y2038@...ts.linaro.org>,
        The etnaviv authors <etnaviv@...ts.freedesktop.org>,
        dri-devel <dri-devel@...ts.freedesktop.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        David Airlie <airlied@...ux.ie>,
        Christian Gmeiner <christian.gmeiner@...il.com>,
        Daniel Vetter <daniel@...ll.ch>,
        Russell King <linux+etnaviv@...linux.org.uk>,
        Emil Velikov <emil.velikov@...labora.com>,
        Sam Ravnborg <sam@...nborg.org>
Subject: Re: [PATCH v2 13/24] drm/etnaviv: reject timeouts with tv_nsec >= NSEC_PER_SEC

On Mon, Jan 20, 2020 at 6:48 PM Lucas Stach <l.stach@...gutronix.de> wrote:
> On Fr, 2020-01-17 at 16:47 +0100, Guido Günther wrote:
> >
> > This breaks rendering here on arm64/gc7000 due to
> >
> > ioctl(6, DRM_IOCTL_ETNAVIV_GEM_CPU_PREP or DRM_IOCTL_MSM_GEM_CPU_PREP, 0xfffff7888680) = -1 EINVAL (Invalid argument)
> > ioctl(6, DRM_IOCTL_ETNAVIV_GEM_CPU_FINI or DRM_IOCTL_QXL_CLIENTCAP, 0xfffff78885e0) = 0
> > ioctl(6, DRM_IOCTL_ETNAVIV_GEM_CPU_PREP or DRM_IOCTL_MSM_GEM_CPU_PREP, 0xfffff7888680) = -1 EINVAL (Invalid argument)
> > ioctl(6, DRM_IOCTL_ETNAVIV_GEM_CPU_FINI or DRM_IOCTL_QXL_CLIENTCAP, 0xfffff78885e0) = 0
> > ioctl(6, DRM_IOCTL_ETNAVIV_GEM_CPU_PREP or DRM_IOCTL_MSM_GEM_CPU_PREP, 0xfffff7888680) = -1 EINVAL (Invalid argument)
> > ioctl(6, DRM_IOCTL_ETNAVIV_GEM_CPU_FINI or DRM_IOCTL_QXL_CLIENTCAP, 0xfffff78885e0) = 0
> >
> > This is due to
> >
> >     get_abs_timeout(&req.timeout, 5000000000);
> >
> > in etna_bo_cpu_prep which can exceed NSEC_PER_SEC.
> >
> > Should i send a patch to revert that change since it breaks existing userspace?
>
> No need to revert. This patch has not been applied to the etnaviv tree
> yet, I guess it's just in one of Arnds branches feeding into -next.
>
> That part of userspace is pretty dumb, as it misses to renormalize
> tv_nsec when it overflows the second boundary. So if what I see is
> correct it should be enough to allow 2 * NSEC_PER_SEC, which should
> both reject broken large timeout and keep existing userspace working.

Ah, so it's never more than 2 billion nanoseconds in known user space?
I can definitely change my patch (actually add one on top) to allow that
and handle it as before, or alternatively accept any 64-bit nanosecond value
as arm64 already did, but make it less inefficient to handle.

       Arnd