linux-kernel - Re: [PATCH v4 3/8] iommu/vt-d: Duplicate iommu_resv

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Date:   Mon, 27 May 2019 17:23:04 +0200
From:   Joerg Roedel <joro@...tes.org>
To:     Eric Auger <eric.auger@...hat.com>
Cc:     eric.auger.pro@...il.com, iommu@...ts.linux-foundation.org,
        linux-kernel@...r.kernel.org, dwmw2@...radead.org,
        lorenzo.pieralisi@....com, robin.murphy@....com,
        will.deacon@....com, hanjun.guo@...aro.org, sudeep.holla@....com,
        alex.williamson@...hat.com, shameerali.kolothum.thodi@...wei.com
Subject: Re: [PATCH v4 3/8] iommu/vt-d: Duplicate iommu_resv_region objects
 per device list

On Mon, May 27, 2019 at 10:55:36AM +0200, Eric Auger wrote:
> -			list_add_tail(&rmrr->resv->list, head);
> +			length = rmrr->end_address - rmrr->base_address + 1;
> +			resv = iommu_alloc_resv_region(rmrr->base_address,
> +						       length, prot,
> +						       IOMMU_RESV_DIRECT,
> +						       GFP_ATOMIC);
> +			if (!resv)
> +				break;
> +
> +			list_add_tail(&resv->list, head);

Okay, so this happens in a rcu_read_locked section and must be atomic,
but I don't like this extra parameter to iommu_alloc_resv_region().

How about replacing the rcu-lock with the dmar_global_lock, which
protects against changes to the global rmrr list? This will make this
loop preemptible and taking the global lock is okay because this
function is in no way performance relevant.

Regards,

	Joerg