linux-kernel - Re: [PATCH v5 04/12] iommu/vt-d: Add 256-bit invalidation descriptor support

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Message-ID: <3b0eadd2-b99f-98d6-594f-0419f0542789@linux.intel.com>
Date:   Tue, 4 Dec 2018 14:13:31 +0800
From:   Lu Baolu <baolu.lu@...ux.intel.com>
To:     "Liu, Yi L" <yi.l.liu@...el.com>, Joerg Roedel <joro@...tes.org>
Cc:     baolu.lu@...ux.intel.com, David Woodhouse <dwmw2@...radead.org>,
        "Raj, Ashok" <ashok.raj@...el.com>,
        "Kumar, Sanjay K" <sanjay.k.kumar@...el.com>,
        "Pan, Jacob jun" <jacob.jun.pan@...el.com>,
        "Tian, Kevin" <kevin.tian@...el.com>,
        "Sun, Yi Y" <yi.y.sun@...el.com>,
        "peterx@...hat.com" <peterx@...hat.com>,
        Jean-Philippe Brucker <jean-philippe.brucker@....com>,
        "iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Jacob Pan <jacob.jun.pan@...ux.intel.com>
Subject: Re: [PATCH v5 04/12] iommu/vt-d: Add 256-bit invalidation descriptor
 support

Hi,

On 12/4/18 1:23 AM, Liu, Yi L wrote:
> Hi Joerg,
> 
>> From: Joerg Roedel [mailto:joro@...tes.org]
>> Sent: Monday, December 3, 2018 5:49 AM
>> To: Lu Baolu <baolu.lu@...ux.intel.com>
>> Subject: Re: [PATCH v5 04/12] iommu/vt-d: Add 256-bit invalidation descriptor
>> support
>>
>> On Wed, Nov 28, 2018 at 11:54:41AM +0800, Lu Baolu wrote:
>>> -
>>> -	desc_page = alloc_pages_node(iommu->node, GFP_ATOMIC | __GFP_ZERO,
>> 0);
>>> +	/*
>>> +	 * Need two pages to accommodate 256 descriptors of 256 bits each
>>> +	 * if the remapping hardware supports scalable mode translation.
>>> +	 */
>>> +	desc_page = alloc_pages_node(iommu->node, GFP_ATOMIC | __GFP_ZERO,
>>> +				     !!ecap_smts(iommu->ecap));
>>
>>
>> Same here, does the allocation really need GFP_ATOMIC?
> 
> still leave to Baolu.

The existing code uses GFP_ATOMIC, this patch only changes the size of
the allocated desc_page.

I don't think we really need GFP_ATOMIC here (and also for some other
places). I will clean up them in a separated patch.

> 
>>
>>>   struct q_inval {
>>>   	raw_spinlock_t  q_lock;
>>> -	struct qi_desc  *desc;          /* invalidation queue */
>>> +	void		*desc;          /* invalidation queue */
>>>   	int             *desc_status;   /* desc status */
>>>   	int             free_head;      /* first free entry */
>>>   	int             free_tail;      /* last free entry */
>>
>> Why do you switch the pointer to void* ?
> 
> In this patch, there is some code like the code below. It calculates
> destination address of memcpy with qi->desc. If it's still struct qi_desc
> pointer, the calculation result would be wrong.
> 
> +			memcpy(desc, qi->desc + (wait_index << shift),
> +			       1 << shift);
> 
> The change of the calculation method is to support 128 bits invalidation
> descriptors and 256 invalidation descriptors in this unified code logic.
> 
> Also, the conversation between Baolu and me may help.
> 
> https://lore.kernel.org/patchwork/patch/1006756/

Yes. We need to support different descriptor size.

Best regards,
Lu Baolu