[prev in list] [next in list] [prev in thread] [next in thread] 

List:       linux-rdma
Subject:    Re: [PATCH v19 02/15] arm64: Introduce prctl() options to control the tagged user addresses ABI
From:       Dave Hansen <dave.hansen () intel ! com>
Date:       2019-07-31 17:05:15
Message-ID: 7a34470c-73f0-26ac-e63d-161191d4b1e4 () intel ! com
[Download RAW message or body]

On 7/23/19 10:58 AM, Andrey Konovalov wrote:
> +long set_tagged_addr_ctrl(unsigned long arg)
> +{
> +	if (!tagged_addr_prctl_allowed)
> +		return -EINVAL;
> +	if (is_compat_task())
> +		return -EINVAL;
> +	if (arg & ~PR_TAGGED_ADDR_ENABLE)
> +		return -EINVAL;
> +
> +	update_thread_flag(TIF_TAGGED_ADDR, arg & PR_TAGGED_ADDR_ENABLE);
> +
> +	return 0;
> +}

Instead of a plain enable/disable, a more flexible ABI would be to have
the tag mask be passed in.  That way, an implementation that has a
flexible tag size can select it.  It also ensures that userspace
actually knows what the tag size is and isn't surprised if a hardware
implementation changes the tag size or position.

Also, this whole set deals with tagging/untagging, but there's an
effective loss of address space when you do this.  Is that dealt with
anywhere?  How do we ensure that allocations don't get placed at a
tagged address before this gets turned on?  Where's that checking?
[prev in list] [next in list] [prev in thread] [next in thread]