linux-kernel - Re: [PATCH] intel-iommu: Don't be too aggressive when clearing one context entry

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Date:   Wed, 30 Aug 2017 15:31:12 +0200
From:   Joerg Roedel <joro@...tes.org>
To:     Filippo Sironi <sironi@...zon.de>
Cc:     iommu@...ts.linux-foundation.org, linux-kernel@...r.kernel.org,
        David Woodhouse <dwmw@...zon.co.uk>,
        David Woodhouse <dwmw2@...radead.org>
Subject: Re: [PATCH] intel-iommu: Don't be too aggressive when clearing one
 context entry

Hi Filippo,

please change the subject to:

	iommu/vt-d: Don't be too aggressive when clearing one context entry

to follow the convention used in the iommu-tree. Another comment below.

On Mon, Aug 28, 2017 at 04:16:29PM +0200, Filippo Sironi wrote:
>  static void domain_context_clear_one(struct intel_iommu *iommu, u8 bus, u8 devfn)
>  {
> +	unsigned long flags;
> +	struct context_entry *context;
> +	u16 did_old;
> +
>  	if (!iommu)
>  		return;
>  
> +	spin_lock_irqsave(&iommu->lock, flags);
> +	context = iommu_context_addr(iommu, bus, devfn, 0);
> +	if (!context) {
> +		spin_unlock_irqrestore(&iommu->lock, flags);
> +		return;
> +	}
> +	did_old = context_domain_id(context);
> +	spin_unlock_irqrestore(&iommu->lock, flags);
>  	clear_context_table(iommu, bus, devfn);

This function is the only caller of clear_context_table(), which does
similar things (like fetching the context-entry) as you are adding
above.

So you can either make clear_context_table() return the old domain-id
so that you don't need to do it here, or you get rid of the function
entirely and add the context_clear_entry() and __iommu_flush_cache()
calls into this code-path.

Regards,

	Joerg