Subject: Re: [PATCH kernel v7 26/31] powerpc/iommu: Add userspace view of TCE table

From: Alex Williamson <[email-masked]>
Date: Wed, 08 Apr 2015 09:43:25 -0600

On Wed, 2015-04-08 at 13:22 +1000, Alexey Kardashevskiy wrote:
> On 04/03/2015 07:50 AM, Alex Williamson wrote:
> >
> > Should have sent this with the other comments, but found it hiding on my
> > desktop...
> >
> > On Sat, 2015-03-28 at 01:55 +1100, 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]>
> >> ---
> >>   arch/powerpc/include/asm/iommu.h          |  6 ++++++
> >>   arch/powerpc/kernel/iommu.c               |  7 +++++++
> >>   arch/powerpc/platforms/powernv/pci-ioda.c | 23 ++++++++++++++++++++++-
> >>   3 files changed, 35 insertions(+), 1 deletion(-)
> >>
> >> diff --git a/arch/powerpc/include/asm/iommu.h b/arch/powerpc/include/asm/iommu.h
> >> index 2c08c91..a768a4d 100644
> >> --- a/arch/powerpc/include/asm/iommu.h
> >> +++ b/arch/powerpc/include/asm/iommu.h
> >> @@ -106,9 +106,15 @@ 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_group;
> >> +	unsigned long *it_userspace; /* userspace view of the table */
> >>   	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 0bcd988..82102d1 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>
> >> @@ -1069,6 +1070,9 @@ static int iommu_table_take_ownership(struct iommu_table *tbl)
> >>   		spin_unlock(&tbl->pools[i].lock);
> >>   	spin_unlock_irqrestore(&tbl->large_pool.lock, flags);
> >>
> >> +	BUG_ON(tbl->it_userspace);
> >> +	tbl->it_userspace = vzalloc(sizeof(*tbl->it_userspace) * tbl->it_size);
> >> +
> >
> > -ENOMEM?
> >
> >>   	return 0;
> >>   }
> >>
> >> @@ -1102,6 +1106,9 @@ static void iommu_table_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 bc36cf1..036f3c1 100644
> >> --- a/arch/powerpc/platforms/powernv/pci-ioda.c
> >> +++ b/arch/powerpc/platforms/powernv/pci-ioda.c
> >> @@ -26,6 +26,7 @@
> >>   #include <linux/iommu.h>
> >>   #include <linux/mmzone.h>
> >>   #include <linux/sizes.h>
> >> +#include <linux/vmalloc.h>
> >>
> >>   #include <asm/mmzone.h>
> >>   #include <asm/sections.h>
> >> @@ -1469,6 +1470,9 @@ static void pnv_pci_free_table(struct iommu_table *tbl)
> >>   	if (!tbl->it_size)
> >>   		return;
> >>
> >> +	if (tbl->it_userspace)
> >
> > Not necessary
> 
> Out of curiosity - why? Is every single implementation is known for 
> checking the argument?

AFAIK, all flavors of free in the kernel accept NULL pointers and do the
right thing.  I verified this one does too.

> >> +		vfree(tbl->it_userspace);
> >> +
> >
> > Why no NULL setting this time?
> 
> iommu_reset_table() (2 lines below) will do memset(0) on the entire struct.

So then should iommu_reset_table() handle the vfree() as well?

> >>   	pnv_free_tce_table(tbl->it_base, size, tbl->it_indirect_levels);
> >>   	iommu_reset_table(tbl, "ioda2");
> >>   }
> >> @@ -1656,9 +1660,26 @@ static void pnv_ioda2_set_ownership(struct iommu_table_group *table_group,
> >>   	pnv_pci_ioda2_set_bypass(pe, !enable);
> >>   }
> >>
> >> +static long pnv_pci_ioda2_create_table_with_uas(
> >> +		struct iommu_table_group *table_group,
> >> +		int num, __u32 page_shift, __u64 window_size, __u32 levels,
> >> +		struct iommu_table *tbl)
> >> +{
> >> +	long ret = pnv_pci_ioda2_create_table(table_group, num,
> >> +			page_shift, window_size, levels, tbl);
> >> +
> >> +	if (ret)
> >> +		return ret;
> >> +
> >> +	BUG_ON(tbl->it_userspace);
> >> +	tbl->it_userspace = vzalloc(sizeof(*tbl->it_userspace) * tbl->it_size);
> >
> > -ENOMEM
> >
> >> +
> >> +	return 0;
> >> +}
> >> +
> >>   static struct iommu_table_group_ops pnv_pci_ioda2_ops = {
> >>   	.set_ownership = pnv_ioda2_set_ownership,
> >> -	.create_table = pnv_pci_ioda2_create_table,
> >> +	.create_table = pnv_pci_ioda2_create_table_with_uas,
> >>   	.set_window = pnv_pci_ioda2_set_window,
> >>   	.unset_window = pnv_pci_ioda2_unset_window,
> >>   };
> >
> >
> >
> 
> 
> Thanks for the review! What is overall resume? Another respin?

Is there another option?  It seems like there are too many issues to
simply fold cleanups onto the end of the series.  Thanks,

Alex