linux-kernel - Re: [PATCH v4 04/12] iommu/vt-d: Add 256-bit invalidation descriptor support

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Message-ID: <915876cd-6a1f-097b-b9be-9cb3df18a1df@linux.intel.com>
Date:   Thu, 8 Nov 2018 13:24:40 +0800
From:   Lu Baolu <baolu.lu@...ux.intel.com>
To:     "Liu, Yi L" <yi.l.liu@...el.com>, Joerg Roedel <joro@...tes.org>,
        David Woodhouse <dwmw2@...radead.org>
Cc:     baolu.lu@...ux.intel.com, "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 v4 04/12] iommu/vt-d: Add 256-bit invalidation descriptor
 support

Hi,

On 11/8/18 11:49 AM, Liu, Yi L wrote:
> Hi,
> 
>> From: Lu Baolu [mailto:baolu.lu@...ux.intel.com]
>> Sent: Thursday, November 8, 2018 10:17 AM
>> Subject: Re: [PATCH v4 04/12] iommu/vt-d: Add 256-bit invalidation descriptor
>> support
>>
>> Hi Yi,
>>
>> On 11/7/18 2:07 PM, Liu, Yi L wrote:
>>> Hi Baolu,
>>>
>>>> From: Lu Baolu [mailto:baolu.lu@...ux.intel.com]
>>>> Sent: Monday, November 5, 2018 1:32 PM
>>>
>>> [...]
>>>
>>>> ---
>>>>    drivers/iommu/dmar.c                | 83 +++++++++++++++++++----------
>>>>    drivers/iommu/intel-svm.c           | 76 ++++++++++++++++----------
>>>>    drivers/iommu/intel_irq_remapping.c |  6 ++-
>>>>    include/linux/intel-iommu.h         |  9 +++-
>>>>    4 files changed, 115 insertions(+), 59 deletions(-)
>>>>
>>>> diff --git a/drivers/iommu/dmar.c b/drivers/iommu/dmar.c index
>>>> d9c748b6f9e4..ec10427b98ac 100644
>>>> --- a/drivers/iommu/dmar.c
>>>> +++ b/drivers/iommu/dmar.c
>>>> @@ -1160,6 +1160,7 @@ static int qi_check_fault(struct intel_iommu
>>>> *iommu, int
>>>> index)
>>>>    	int head, tail;
>>>>    	struct q_inval *qi = iommu->qi;
>>>>    	int wait_index = (index + 1) % QI_LENGTH;
>>>> +	int shift = qi_shift(iommu);
>>>>
>>>>    	if (qi->desc_status[wait_index] == QI_ABORT)
>>>>    		return -EAGAIN;
>>>> @@ -1173,13 +1174,15 @@ static int qi_check_fault(struct intel_iommu
>>>> *iommu, int index)
>>>>    	 */
>>>>    	if (fault & DMA_FSTS_IQE) {
>>>>    		head = readl(iommu->reg + DMAR_IQH_REG);
>>>> -		if ((head >> DMAR_IQ_SHIFT) == index) {
>>>> +		if ((head >> shift) == index) {
>>>> +			struct qi_desc *desc = qi->desc + head;
>>>> +
>>>>    			pr_err("VT-d detected invalid descriptor: "
>>>>    				"low=%llx, high=%llx\n",
>>>> -				(unsigned long long)qi->desc[index].low,
>>>> -				(unsigned long long)qi->desc[index].high);
>>>> -			memcpy(&qi->desc[index], &qi->desc[wait_index],
>>>> -					sizeof(struct qi_desc));
>>>> +				(unsigned long long)desc->qw0,
>>>> +				(unsigned long long)desc->qw1);
>>>
>>> Still missing qw2 and qw3. May make the print differ based on if smts is configed.
>>
>> qw2 and qw3 are reserved from software point of view. We don't need to print it for
>> information.
> 
> But for Scalable mode, it should be valid?

No. It's reserved for software.

> 
>>
>>>
>>>> +			memcpy(desc, qi->desc + (wait_index << shift),
>>>
>>> Would "memcpy(desc, (unsigned long long) (qi->desc +  (wait_index <<
>>> shift)," be more safe?
>>
>> Can that be compiled? memcpy() requires a "const void *" for the second parameter.
>> By the way, why it's safer with this casting?
> 
> This is just an example. My point is the possibility that "qi->desc + (wait_index << shift)"
> would be treated as "qi->desc plus (wait_index << shift)*sizeof(*qi->desc)". Is it possible
> for kernel build?

qi->desc is of type of "void *".

Best regards,
Lu Baolu