linux-kernel - Re: [RFC v3 07/15] iommu: iommu_get/put_single

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Message-ID: <20160218110616.05108071@arm.com>
Date:	Thu, 18 Feb 2016 11:06:16 +0000
From:	Marc Zyngier <marc.zyngier@....com>
To:	Eric Auger <eric.auger@...aro.org>
Cc:	eric.auger@...com, alex.williamson@...hat.com, will.deacon@....com,
	joro@...tes.org, tglx@...utronix.de, jason@...edaemon.net,
	christoffer.dall@...aro.org, linux-arm-kernel@...ts.infradead.org,
	kvmarm@...ts.cs.columbia.edu, kvm@...r.kernel.org,
	suravee.suthikulpanit@....com, patches@...aro.org,
	linux-kernel@...r.kernel.org, Manish.Jaggi@...iumnetworks.com,
	Bharat.Bhushan@...escale.com, pranav.sawargaonkar@...il.com,
	p.fedin@...sung.com, iommu@...ts.linux-foundation.org,
	sherry.hurwitz@....com, brijesh.singh@....com, leo.duran@....com,
	Thomas.Lendacky@....com
Subject: Re: [RFC v3 07/15] iommu: iommu_get/put_single_reserved

On Fri, 12 Feb 2016 08:13:09 +0000
Eric Auger <eric.auger@...aro.org> wrote:

> This patch introduces iommu_get/put_single_reserved.
> 
> iommu_get_single_reserved allows to allocate a new reserved iova page
> and map it onto the physical page that contains a given physical address.
> It returns the iova that is mapped onto the provided physical address.
> Hence the physical address passed in argument does not need to be aligned.
> 
> In case a mapping already exists between both pages, the IOVA mapped
> to the PA is directly returned.
> 
> Each time an iova is successfully returned a binding ref count is
> incremented.
> 
> iommu_put_single_reserved decrements the ref count and when this latter
> is null, the mapping is destroyed and the iova is released.

I wonder if there is a requirement for the caller to find out about the
size of the mapping, or to impose a given size... MSIs clearly do not
have that requirement (this is always a 32bit value), but since
allocations usually pair address and size, I though I'd ask...

Thanks,

	M.
-- 
Jazz is not dead. It just smells funny.