linux-kernel - Re: [PATCH 1/2] habanalabs: support vmalloc memory mapping

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Date:   Fri, 11 Oct 2019 02:26:22 -0700
From:   Christoph Hellwig <hch@...radead.org>
To:     Oded Gabbay <oded.gabbay@...il.com>
Cc:     Christoph Hellwig <hch@...radead.org>,
        Omer Shpigelman <oshpigelman@...ana.ai>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/2] habanalabs: support vmalloc memory mapping

On Fri, Oct 11, 2019 at 12:19:36PM +0300, Oded Gabbay wrote:
> We first allocate, using vmalloc_user, a certain memory block that
> will be used by the ASIC and the user (ASIC is producer, user is
> consumer).
> After we use vmalloc_user, we map the *kernel* pointer we got from the
> vmalloc_user() to the ASIC MMU. We reuse our driver's generic code
> path to map host memory to ASIC MMU and that's why we need the patch
> above. The user does NOT send us the pointer. He doesn't have this
> pointer. It is internal to the kernel driver. To do this reuse, we
> added a call to the is_vmalloc_addr(), so the function will know if it
> is called to work on user pointers, or on vmalloc *kernel* pointers.

But the function can't decided that.  As I said before you can't just
take a value that possibly contains user pointers and call
is_vmalloc_addr on it, as kernel and user address can overlap on
various architectures.

You need to restructure your code to keep the kernel and user pointer
code paths entirely separate.