Re: [Xen-devel] [PATCH v13 1/4] remove late (on-demand) construction of IOMMU page tables

From: Wei Liu <wl@xen.org>
To: Paul Durrant <paul.durrant@citrix.com>
Cc: "Petre Pircalabu" <ppircalabu@bitdefender.com>,
	"Stefano Stabellini" <sstabellini@kernel.org>,
	"Wei Liu" <wl@xen.org>,
	"Razvan Cojocaru" <rcojocaru@bitdefender.com>,
	"Konrad Rzeszutek Wilk" <konrad.wilk@oracle.com>,
	"George Dunlap" <George.Dunlap@eu.citrix.com>,
	"Andrew Cooper" <andrew.cooper3@citrix.com>,
	"Ian Jackson" <ian.jackson@eu.citrix.com>,
	"Tim Deegan" <tim@xen.org>, "Julien Grall" <julien.grall@arm.com>,
	"Tamas K Lengyel" <tamas@tklengyel.com>,
	"Jan Beulich" <jbeulich@suse.com>,
	"Alexandru Isaila" <aisaila@bitdefender.com>,
	xen-devel@lists.xenproject.org,
	"Volodymyr Babchuk" <Volodymyr_Babchuk@epam.com>,
	"Roger Pau Monné" <roger.pau@citrix.com>
Subject: Re: [Xen-devel] [PATCH v13 1/4] remove late (on-demand) construction of IOMMU page tables
Date: Wed, 25 Sep 2019 10:16:50 +0100	[thread overview]
Message-ID: <20190925091650.qgnfkabob6zrfebd@debian> (raw)
In-Reply-To: <20190918104113.3294-2-paul.durrant@citrix.com>

On Wed, Sep 18, 2019 at 11:41:10AM +0100, Paul Durrant wrote:
> Now that there is a per-domain IOMMU-enable flag, which should be set if
> any device is going to be passed through, stop deferring page table
> construction until the assignment is done. Also don't tear down the tables
> again when the last device is de-assigned; defer that task until domain
> destruction.
> 
> This allows the has_iommu_pt() helper and iommu_status enumeration to be
> removed. Calls to has_iommu_pt() are simply replaced by calls to
> is_iommu_enabled(). Remaining open-coded tests of iommu_hap_pt_share can
> also be replaced by calls to iommu_use_hap_pt().
> The arch_iommu_populate_page_table() and iommu_construct() functions become
> redundant, as does the 'strict mode' dom0 page_list mapping code in
> iommu_hwdom_init(), and iommu_teardown() can be made static is its only
> remaining caller, iommu_domain_destroy(), is within the same source
> module.
> 
> All in all, about 220 lines of code are removed from the hypervisor (at
> the expense of some additions in the toolstack).
> 
> NOTE: This patch will cause a small amount of extra resource to be used
>       to accommodate IOMMU page tables that may never be used, since the
>       per-domain IOMMU-enable flag is currently set to the value of the
>       global iommu_enable flag. A subsequent patch will add an option to
>       the toolstack to allow it to be turned off if there is no intention
>       to assign passthrough hardware to the domain.
>       To account for the extra resource, 'iommu_memkb' has been added to
>       domain_build_info. This patch sets it to a value calculated based
>       on the domain's maximum memory when the P2M sharing is either not
>       supported or globally disabled, or zero otherwise. However, when
>       the toolstack option mentioned above is added, it will also be zero
>       if the per-domain IOMMU-enable flag is turned off.
> 
> Signed-off-by: Paul Durrant <paul.durrant@citrix.com>
> Reviewed-by: Alexandru Isaila <aisaila@bitdefender.com>
> Acked-by: Razvan Cojocaru <rcojocaru@bitdefender.com>
> Reviewed-by: Jan Beulich <jbeulich@suse.com>
> Acked-by: Julien Grall <julien.grall@arm.com>

Acked-by: Wei Liu <wl@xen.org>

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