Subject: Re: [PATCH kernel v9 26/32] powerpc/iommu: Add userspace view of TCE table

From: David Gibson <[email-masked]>
Date: Wed, 29 Apr 2015 16:31:13 +1000

On Sat, Apr 25, 2015 at 10:14:50PM +1000, Alexey Kardashevskiy wrote:
> In order to support memory pre-registration, we need a way to track
> the use of every registered memory region and only allow unregistration
> if a region is not in use anymore. So we need a way to tell from what
> region the just cleared TCE was from.
> 
> This adds a userspace view of the TCE table into iommu_table struct.
> It contains userspace address, one per TCE entry. The table is only
> allocated when the ownership over an IOMMU group is taken which means
> it is only used from outside of the powernv code (such as VFIO).
> 
> Signed-off-by: Alexey Kardashevskiy <[email-masked]>
> ---
> Changes:
> v9:
> * fixed code flow in error cases added in v8
> 
> v8:
> * added ENOMEM on failed vzalloc()
> ---
>  arch/powerpc/include/asm/iommu.h          |  6 ++++++
>  arch/powerpc/kernel/iommu.c               | 18 ++++++++++++++++++
>  arch/powerpc/platforms/powernv/pci-ioda.c | 22 ++++++++++++++++++++--
>  3 files changed, 44 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/powerpc/include/asm/iommu.h b/arch/powerpc/include/asm/iommu.h
> index 7694546..1472de3 100644
> --- a/arch/powerpc/include/asm/iommu.h
> +++ b/arch/powerpc/include/asm/iommu.h
> @@ -111,9 +111,15 @@ struct iommu_table {
>  	unsigned long *it_map;       /* A simple allocation bitmap for now */
>  	unsigned long  it_page_shift;/* table iommu page size */
>  	struct iommu_table_group *it_table_group;
> +	unsigned long *it_userspace; /* userspace view of the table */

A single unsigned long doesn't seem like enough.  How do you know
which process's address space this address refers to?

>  	struct iommu_table_ops *it_ops;
>  };
>  
> +#define IOMMU_TABLE_USERSPACE_ENTRY(tbl, entry) \
> +		((tbl)->it_userspace ? \
> +			&((tbl)->it_userspace[(entry) - (tbl)->it_offset]) : \
> +			NULL)
> +
>  /* Pure 2^n version of get_order */
>  static inline __attribute_const__
>  int get_iommu_order(unsigned long size, struct iommu_table *tbl)
> diff --git a/arch/powerpc/kernel/iommu.c b/arch/powerpc/kernel/iommu.c
> index 2eaba0c..74a3f52 100644
> --- a/arch/powerpc/kernel/iommu.c
> +++ b/arch/powerpc/kernel/iommu.c
> @@ -38,6 +38,7 @@
>  #include <linux/pci.h>
>  #include <linux/iommu.h>
>  #include <linux/sched.h>
> +#include <linux/vmalloc.h>
>  #include <asm/io.h>
>  #include <asm/prom.h>
>  #include <asm/iommu.h>
> @@ -739,6 +740,8 @@ void iommu_reset_table(struct iommu_table *tbl, const char *node_name)
>  		free_pages((unsigned long) tbl->it_map, order);
>  	}
>  
> +	WARN_ON(tbl->it_userspace);
> +
>  	memset(tbl, 0, sizeof(*tbl));
>  }
>  
> @@ -1016,6 +1019,7 @@ int iommu_take_ownership(struct iommu_table *tbl)
>  {
>  	unsigned long flags, i, sz = (tbl->it_size + 7) >> 3;
>  	int ret = 0;
> +	unsigned long *uas;
>  
>  	/*
>  	 * VFIO does not control TCE entries allocation and the guest
> @@ -1027,6 +1031,10 @@ int iommu_take_ownership(struct iommu_table *tbl)
>  	if (!tbl->it_ops->exchange)
>  		return -EINVAL;
>  
> +	uas = vzalloc(sizeof(*uas) * tbl->it_size);
> +	if (!uas)
> +		return -ENOMEM;
> +
>  	spin_lock_irqsave(&tbl->large_pool.lock, flags);
>  	for (i = 0; i < tbl->nr_pools; i++)
>  		spin_lock(&tbl->pools[i].lock);
> @@ -1044,6 +1052,13 @@ int iommu_take_ownership(struct iommu_table *tbl)
>  		memset(tbl->it_map, 0xff, sz);
>  	}
>  
> +	if (ret) {
> +		vfree(uas);
> +	} else {
> +		BUG_ON(tbl->it_userspace);
> +		tbl->it_userspace = uas;
> +	}
> +
>  	for (i = 0; i < tbl->nr_pools; i++)
>  		spin_unlock(&tbl->pools[i].lock);
>  	spin_unlock_irqrestore(&tbl->large_pool.lock, flags);
> @@ -1056,6 +1071,9 @@ void iommu_release_ownership(struct iommu_table *tbl)
>  {
>  	unsigned long flags, i, sz = (tbl->it_size + 7) >> 3;
>  
> +	vfree(tbl->it_userspace);
> +	tbl->it_userspace = NULL;
> +
>  	spin_lock_irqsave(&tbl->large_pool.lock, flags);
>  	for (i = 0; i < tbl->nr_pools; i++)
>  		spin_lock(&tbl->pools[i].lock);
> diff --git a/arch/powerpc/platforms/powernv/pci-ioda.c b/arch/powerpc/platforms/powernv/pci-ioda.c
> index 45bc131..e0be556 100644
> --- a/arch/powerpc/platforms/powernv/pci-ioda.c
> +++ b/arch/powerpc/platforms/powernv/pci-ioda.c
> @@ -25,6 +25,7 @@
>  #include <linux/memblock.h>
>  #include <linux/iommu.h>
>  #include <linux/sizes.h>
> +#include <linux/vmalloc.h>
>  
>  #include <asm/sections.h>
>  #include <asm/io.h>
> @@ -1827,6 +1828,14 @@ static void pnv_ioda2_tce_free(struct iommu_table *tbl, long index,
>  		pnv_pci_ioda2_tce_invalidate(tbl, index, npages, false);
>  }
>  
> +void pnv_pci_ioda2_free_table(struct iommu_table *tbl)
> +{
> +	vfree(tbl->it_userspace);
> +	tbl->it_userspace = NULL;
> +
> +	pnv_pci_free_table(tbl);
> +}
> +
>  static struct iommu_table_ops pnv_ioda2_iommu_ops = {
>  	.set = pnv_ioda2_tce_build,
>  #ifdef CONFIG_IOMMU_API
> @@ -1834,7 +1843,7 @@ static struct iommu_table_ops pnv_ioda2_iommu_ops = {
>  #endif
>  	.clear = pnv_ioda2_tce_free,
>  	.get = pnv_tce_get,
> -	.free = pnv_pci_free_table,
> +	.free = pnv_pci_ioda2_free_table,
>  };
>  
>  static void pnv_pci_ioda_setup_opal_tce_kill(struct pnv_phb *phb,
> @@ -2062,12 +2071,21 @@ static long pnv_pci_ioda2_create_table(struct iommu_table_group *table_group,
>  	int nid = pe->phb->hose->node;
>  	__u64 bus_offset = num ? pe->tce_bypass_base : 0;
>  	long ret;
> +	unsigned long *uas, uas_cb = sizeof(*uas) * (window_size >> page_shift);
> +
> +	uas = vzalloc(uas_cb);
> +	if (!uas)
> +		return -ENOMEM;

I don't see why this is allocated both here as well as in
take_ownership.  Isn't this function used for core-kernel users of the
iommu as well, in which case it shouldn't need the it_userspace.

>  	ret = pnv_pci_create_table(table_group, nid, bus_offset, page_shift,
>  			window_size, levels, tbl);
> -	if (ret)
> +	if (ret) {
> +		vfree(uas);
>  		return ret;
> +	}
>  
> +	BUG_ON(tbl->it_userspace);
> +	tbl->it_userspace = uas;
>  	tbl->it_ops = &pnv_ioda2_iommu_ops;
>  	if (pe->tce_inval_reg)
>  		tbl->it_type |= (TCE_PCI_SWINV_CREATE | TCE_PCI_SWINV_FREE);

-- 
David Gibson			| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you.  NOT _the_ _other_
				| _way_ _around_!
http://www.ozlabs.org/~dgibson