linux-kernel - Re: [PATCH] iommu/amd: Fix logics to determine and checking max PASID

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Date:	Wed, 5 Mar 2014 16:46:58 -0600
From:	Suravee Suthikulanit <suravee.suthikulpanit@....com>
To:	Joerg Roedel <joro@...tes.org>
CC:	<iommu@...ts.linux-foundation.org>, <linux-kernel@...r.kernel.org>,
	<kim.naru@....com>, <jay.cornwall@....com>
Subject: Re: [PATCH] iommu/amd: Fix logics to determine and checking max PASID

Joerg,

Other commands can still support upto 20-bit PASID. As I mentioned, 
there is still no system with more than 16-bit PASID.

Either way, I have also replaced the PASID_MASK with the value derived 
from MMIOx30h[PASmax] of the IOMMU Extended Feature register instead.
This should allow us not to have to change the mask things again for 
future hardware.

We just need to revisit this BUG_ON() part when the new spec comes.

Suravee


On 3/5/2014 4:35 PM, Joerg Roedel wrote:
> On Wed, Mar 05, 2014 at 01:01:08PM -0600, suravee.suthikulpanit@....com wrote:
>>   drivers/iommu/amd_iommu.c       |   26 +++++++++++++++++++++++---
>>   drivers/iommu/amd_iommu_init.c  |   15 ++++++++-------
>>   drivers/iommu/amd_iommu_types.h |    6 ++----
>>   drivers/iommu/amd_iommu_v2.c    |    2 +-
>>   4 files changed, 34 insertions(+), 15 deletions(-)
>
> Hmm, this looks a bit complicated. Since the inv_iotlb_pasid and
> complete_ppr command only support 16 bit pasids by specification, there
> is no way to support pasids with more than 16 bits in general anymore. I
> think the best way to handle it is to just change the PASID_MASK to
> 0x0000ffff.
>
>>   static void build_inv_iotlb_pasid(struct iommu_cmd *cmd, u16 devid, int pasid,
>>   				  int qdep, u64 address, bool size)
>>   {
>> +	/* Note:
>> +	 * This command supports only 16-bit PASID.
>> +	 * Currently, hardware only implement upto 16-bit PASID
>> +	 * even though the spec says it could have upto 20 bits.
>> +	 * This is likely to be updated in the future revision of
>> +	 * IOMMU specs when the hardware with PASID > 16 bits
>> +	 * become available.
>> +	 */
>> +	BUG_ON(pasid > 0xFFFF);
>
> We can keep this as BUG_ON(pasid & ~PASID_MASK), but then ...
>
>> -		cmd->data[1]  = pasid & PASID_MASK;
>> +		cmd->data[1]  = pasid & amd_iommu_max_pasid;
>
> ... masking out the other bits is redundant.
>
>
> 	Joerg
>
>
>


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