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

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Date:	Wed, 5 Mar 2014 23:35:45 +0100
From:	Joerg Roedel <joro@...tes.org>
To:	suravee.suthikulpanit@....com
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

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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