linux-kernel - Re: [PATCH] iommu/vt-d: Fix the size calculation of pasid table

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Date:   Mon, 10 Oct 2016 21:00:14 +0800
From:   Xunlei Pang <xpang@...hat.com>
To:     David Woodhouse <dwmw2@...radead.org>
Cc:     Joerg Roedel <joro@...tes.org>, Xunlei Pang <xlpang@...hat.com>,
        iommu@...ts.linux-foundation.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] iommu/vt-d: Fix the size calculation of pasid table

Ping David for confirmation

On 2016/09/19 at 20:18, Joerg Roedel wrote:
> [Cc'ing David]
>
> On Mon, Sep 12, 2016 at 10:49:11AM +0800, Xunlei Pang wrote:
>> According to the vt-d spec, the size of pasid (state) entry is 8B
>> which equals 3 in power of 2, the number of pasid (state) entries
>> is (ecap_pss + 1) in power of 2.
>>
>> Thus the right size of pasid (state) table in power of 2 should be
>> ecap_pss(iommu->ecap) plus "1+3=4" other than 7.
>>
>> Signed-off-by: Xunlei Pang <xlpang@...hat.com>
>> ---
>>  drivers/iommu/intel-svm.c | 2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/drivers/iommu/intel-svm.c b/drivers/iommu/intel-svm.c
>> index 8ebb353..cfa75c2 100644
>> --- a/drivers/iommu/intel-svm.c
>> +++ b/drivers/iommu/intel-svm.c
>> @@ -39,7 +39,7 @@ int intel_svm_alloc_pasid_tables(struct intel_iommu *iommu)
>>  	struct page *pages;
>>  	int order;
>>  
>> -	order = ecap_pss(iommu->ecap) + 7 - PAGE_SHIFT;
>> +	order = ecap_pss(iommu->ecap) + 4 - PAGE_SHIFT;
>>  	if (order < 0)
>>  		order = 0;
> The patch seems to be correct, but I'll let David comment on it first.
>
>
>
> 	Joerg
>