linux-kernel - Re: [PATCH v8 05/13] iommu/amd: Add function copy_dev

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Date:   Thu, 27 Jul 2017 17:29:25 +0200
From:   Joerg Roedel <jroedel@...e.de>
To:     Baoquan He <bhe@...hat.com>
Cc:     iommu@...ts.linux-foundation.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v8 05/13] iommu/amd: Add function copy_dev_tables()

On Fri, Jul 21, 2017 at 04:59:03PM +0800, Baoquan He wrote:
> Add function copy_dev_tables to copy the old DEV table entries of the panicked

Since there is only one (for now), you can name the function in
singular: copy_dev_table() or copy_device_table().

> kernel to the new allocated DEV table. Since all iommus share the same DTE table
> the copy only need be done one time. Besides, we also need to:
> 
>   - Check whether all IOMMUs actually use the same device table with the same size
> 
>   - Verify that the size of the old device table is the expected size.
> 
>   - Reserve the old domain id occupied in 1st kernel to avoid touching the old
>     io-page tables. Then on-flight DMA can continue looking it up.
> 
> And also define MACRO DEV_DOMID_MASK to replace magic number 0xffffULL, it can be
> reused in copy_dev_tables().
> 
> Signed-off-by: Baoquan He <bhe@...hat.com>
> ---
>  drivers/iommu/amd_iommu.c       |  2 +-
>  drivers/iommu/amd_iommu_init.c  | 55 +++++++++++++++++++++++++++++++++++++++++
>  drivers/iommu/amd_iommu_types.h |  1 +
>  3 files changed, 57 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/iommu/amd_iommu.c b/drivers/iommu/amd_iommu.c
> index e5a03f259986..4d00f1bda900 100644
> --- a/drivers/iommu/amd_iommu.c
> +++ b/drivers/iommu/amd_iommu.c
> @@ -2086,7 +2086,7 @@ static void set_dte_entry(u16 devid, struct protection_domain *domain, bool ats)
>  		flags    |= tmp;
>  	}
>  
> -	flags &= ~(0xffffUL);
> +	flags &= ~DEV_DOMID_MASK;
>  	flags |= domain->id;
>  
>  	amd_iommu_dev_table[devid].data[1]  = flags;
> diff --git a/drivers/iommu/amd_iommu_init.c b/drivers/iommu/amd_iommu_init.c
> index f6da5fe03b31..c58f091ce232 100644
> --- a/drivers/iommu/amd_iommu_init.c
> +++ b/drivers/iommu/amd_iommu_init.c
> @@ -842,6 +842,61 @@ static int get_dev_entry_bit(u16 devid, u8 bit)
>  }
>  
>  
> +static int copy_dev_tables(void)
> +{
> +	struct dev_table_entry *old_devtb = NULL;
> +	u32 lo, hi, devid, old_devtb_size;
> +	phys_addr_t old_devtb_phys;
> +	u64 entry, last_entry = 0;
> +	struct amd_iommu *iommu;
> +	u16 dom_id, dte_v;
> +	static int copied;
> +
> +	for_each_iommu(iommu) {
> +		if (!translation_pre_enabled(iommu)) {
> +			pr_err("IOMMU:%d is not pre-enabled!/n",
> +				iommu->index);
> +			return -1;
> +		}
> +
> +		/* All IOMMUs should use the same device table with the same size */
> +		lo = readl(iommu->mmio_base + MMIO_DEV_TABLE_OFFSET);
> +		hi = readl(iommu->mmio_base + MMIO_DEV_TABLE_OFFSET + 4);
> +		entry = (((u64) hi) << 32) + lo;
> +		if (last_entry && last_entry != entry) {
> +			pr_err("IOMMU:%d should use the same dev table as others!/n",
> +				iommu->index);
> +			return -1;
> +		}
> +		last_entry = entry;
> +
> +		old_devtb_size = ((entry & ~PAGE_MASK) + 1) << 12;
> +		if (old_devtb_size != dev_table_size) {
> +			pr_err("The device table size of IOMMU:%d is not expected!/n",
> +				iommu->index);
> +			return -1;
> +		}

I think the loop can end here. There is only one table to copy, so you
don't need to copy it for every iommu. Just do the checks in the loop
and the copy once after the loop.

> +
> +		old_devtb_phys = entry & PAGE_MASK;
> +		old_devtb = memremap(old_devtb_phys, dev_table_size, MEMREMAP_WB);
> +		if (!old_devtb)
> +			return -1;
> +
> +		if (copied)
> +			continue;
> +		for (devid = 0; devid <= amd_iommu_last_bdf; ++devid) {
> +			amd_iommu_dev_table[devid] = old_devtb[devid];
> +			dom_id = old_devtb[devid].data[1] & DEV_DOMID_MASK;
> +			dte_v = old_devtb[devid].data[0] & DTE_FLAG_V;
> +			if (dte_v && dom_id)
> +				__set_bit(dom_id, amd_iommu_pd_alloc_bitmap);
> +		}

Please only copy the DTE when DTE.V is set in the old table. Also
don't copy any of the IOMMUv2 enablement bits from the old DTE. PRI
faults are recoverable by design and a device shouldn't fail on a
negative answer from the IOMMU.