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Date:   Thu, 8 Aug 2019 09:53:51 +0200
From:   Christoph Hellwig <hch@lst.de>
To:     Mark Rutland <mark.rutland@arm.com>
Cc:     Rob Clark <robdclark@chromium.org>, Christoph Hellwig <hch@lst.de>,
        Rob Clark <robdclark@gmail.com>,
        dri-devel <dri-devel@lists.freedesktop.org>,
        Catalin Marinas <catalin.marinas@arm.com>,
        Will Deacon <will@kernel.org>,
        Maarten Lankhorst <maarten.lankhorst@linux.intel.com>,
        Maxime Ripard <maxime.ripard@bootlin.com>,
        Sean Paul <sean@poorly.run>, David Airlie <airlied@linux.ie>,
        Daniel Vetter <daniel@ffwll.ch>,
        Allison Randal <allison@lohutok.net>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        linux-arm-kernel@lists.infradead.org,
        LKML <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 1/2] drm: add cache support for arm64
Message-ID: <20190808075351.GC30308@lst.de>
References: <20190805211451.20176-1-robdclark@gmail.com> <20190806084821.GA17129@lst.de> <CAJs_Fx6eh1w7c=crMoD5XyEOMzP6orLhqUewErE51cPGYmObBQ@mail.gmail.com> <20190806143457.GF475@lakrids.cambridge.arm.com> <CAJs_Fx4h6SWGmDTLBnV4nmWUFAs_Ge1inxd-dW9aDKgKqmc1eQ@mail.gmail.com> <20190807123807.GD54191@lakrids.cambridge.arm.com>
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On Wed, Aug 07, 2019 at 01:38:08PM +0100, Mark Rutland wrote:
> > I *believe* that there are not alias mappings (that I don't control
> > myself) for pages coming from
> > shmem_file_setup()/shmem_read_mapping_page()..  
> 
> AFAICT, that's regular anonymous memory, so there will be a cacheable
> alias in the linear/direct map.

Yes.  Although shmem is in no way special in that regard.  Even with the
normal dma_alloc_coherent implementation on arm and arm64 we keep the
cacheable alias in the direct mapping and just create a new non-cacheable
one.  The only exception are CMA allocations on 32-bit arm, which do
get remapped to uncachable in place.