linux-kernel - Re: [PATCH v3] iommu/amd: Add support for fast IOTLB flushing

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Message-ID: <20180213132959.kkavgzt37hm7n2tt@8bytes.org>
Date:   Tue, 13 Feb 2018 14:29:59 +0100
From:   Joerg Roedel <joro@...tes.org>
To:     Suravee Suthikulpanit <suravee.suthikulpanit@....com>
Cc:     iommu@...ts.linux-foundation.org, linux-kernel@...r.kernel.org,
        jroedel@...e.de
Subject: Re: [PATCH v3] iommu/amd: Add support for fast IOTLB flushing

Hi Suravee,

thanks for working on this.

On Wed, Jan 31, 2018 at 12:01:14AM -0500, Suravee Suthikulpanit wrote:
> +static void amd_iommu_iotlb_range_add(struct iommu_domain *domain,
> +				      unsigned long iova, size_t size)
> +{
> +	struct amd_iommu_flush_entries *entry, *p;
> +	unsigned long flags;
> +	bool found = false;
> +
> +	spin_lock_irqsave(&amd_iommu_flush_list_lock, flags);

I am not happy with introducing or using global locks when they are not
necessary. Can this be a per-domain lock?

Besides, did you check it makes sense to actually keep track of the
ranges here? My approach would be to just make iotlb_range_add() an noop
and do a full domain flush in iotlb_sync(). But maybe you did
measurements you can share here to show there is a benefit.

	Joerg