linux-kernel - Re: [PATCH v3 03/16] iommu: introduce iommu invalidate API function

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Message-ID: <7f8f90e6-5904-a916-8607-ad64dffb867a@arm.com>
Date:   Wed, 10 Jan 2018 12:00:31 +0000
From:   Jean-Philippe Brucker <jean-philippe.brucker@....com>
To:     Jacob Pan <jacob.jun.pan@...ux.intel.com>
Cc:     "iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Joerg Roedel <joro@...tes.org>,
        David Woodhouse <dwmw2@...radead.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Rafael Wysocki <rafael.j.wysocki@...el.com>,
        Alex Williamson <alex.williamson@...hat.com>,
        Lan Tianyu <tianyu.lan@...el.com>,
        "Liu, Yi L" <yi.l.liu@...ux.intel.com>,
        "Liu@...l.linuxfoundation.org" <Liu@...l.linuxfoundation.org>,
        Jean Delvare <khali@...ux-fr.org>
Subject: Re: [PATCH v3 03/16] iommu: introduce iommu invalidate API function

On 28/12/17 19:25, Jacob Pan wrote:
[...]
>>> + * @size:		2^size of 4K pages, 0 for 4k, 9 for 2MB,
>>> etc.  
>>
>> Having only power of two invalidation seems too restrictive for a
>> software interface. You might have the same problem as above, where
>> the guest or userspace needs to send lots of invalidation requests,
>> They could be multiplexed by passing an arbitrary range instead. How
>> about making @size a __u64?
>>
> Sure if you have such need for non power of two. So it will be __u64 of
> 4k pages?

4k granule would work for us right now, but other architectures may plan
to support arbitrary sizes. The map/unmap API does support arbitrary
sizes, so it might be better to have a byte granularity in @size.

Thanks,
Jean