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SubjectRe: [PATCH] avoid endless loops in lib/swiotlb.c
From
On Thu, 13 Mar 2008 09:13:30 +0000
"Jan Beulich" <jbeulich@novell.com> wrote:

> Commit 681cc5cd3efbeafca6386114070e0bfb5012e249 introduced two
> possibilities for entering an endless loop in lib/swiotlb.c:
>
> - if max_slots is zero (possible if mask is ~0UL)

Yeah, max_slots can not be zero. There are no drivers that have such
mask. I'm not sure that we will have.

I exported a function, iommu_is_span_boundary in lib/iommu-helper.c
that does the same thing that is_span_boundary does for SPARC and
PARISC IOMMUs. iommu_is_span_boundary does this checking. I've
attached a patch to convert swiotlb to use it.

If we need to think about the possibility of handling such mask, I
think that it would be better to create a helper function to handle
this in lib/iommu-helper.c since several IOMMUs do the same thing.


> - if the number of slots requested fits into a swiotlb segment, but is
> too large for the part of a segment which remains after considering
> offset_slots

Sorry, I'm not sure what you mean. Can you give me an actual example
numbers that leads to that?


=
From: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>
Subject: [PATCH] SWIOTLB: use iommu_is_span_boundary helper function

iommu_is_span_boundary in lib/iommu-helper.c was exported for PARISC
IOMMUs (commit 3715863aa142c4f4c5208f5f3e5e9bac06006d2f). SWIOTLB can
use it.

Signed-off-by: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>
---
arch/ia64/Kconfig | 3 +++
arch/x86/Kconfig | 5 ++---
lib/swiotlb.c | 19 ++++++-------------
3 files changed, 11 insertions(+), 16 deletions(-)

diff --git a/arch/ia64/Kconfig b/arch/ia64/Kconfig
index 8fa3faf..a33d7ed 100644
--- a/arch/ia64/Kconfig
+++ b/arch/ia64/Kconfig
@@ -46,6 +46,9 @@ config MMU
config SWIOTLB
bool

+config IOMMU_HELPER
+ bool
+
config GENERIC_LOCKBREAK
bool
default y
diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 237fc12..aff96a7 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -477,9 +477,6 @@ config CALGARY_IOMMU_ENABLED_BY_DEFAULT
Calgary anyway, pass 'iommu=calgary' on the kernel command line.
If unsure, say Y.

-config IOMMU_HELPER
- def_bool (CALGARY_IOMMU || GART_IOMMU)
-
# need this always selected by IOMMU for the VIA workaround
config SWIOTLB
bool
@@ -490,6 +487,8 @@ config SWIOTLB
access 32-bits of memory can be used on systems with more than
3 GB of memory. If unsure, say Y.

+config IOMMU_HELPER
+ def_bool (CALGARY_IOMMU || GART_IOMMU || SWIOTLB)

config NR_CPUS
int "Maximum number of CPUs (2-255)"
diff --git a/lib/swiotlb.c b/lib/swiotlb.c
index 4bb5a11..2c6392a 100644
--- a/lib/swiotlb.c
+++ b/lib/swiotlb.c
@@ -31,6 +31,7 @@

#include <linux/init.h>
#include <linux/bootmem.h>
+#include <linux/iommu-helper.h>

#define OFFSET(val,align) ((unsigned long) \
( (val) & ( (align) - 1)))
@@ -282,15 +283,6 @@ address_needs_mapping(struct device *hwdev, dma_addr_t addr)
return (addr & ~mask) != 0;
}

-static inline unsigned int is_span_boundary(unsigned int index,
- unsigned int nslots,
- unsigned long offset_slots,
- unsigned long max_slots)
-{
- unsigned long offset = (offset_slots + index) & (max_slots - 1);
- return offset + nslots > max_slots;
-}
-
/*
* Allocates bounce buffer and returns its kernel virtual address.
*/
@@ -334,8 +326,8 @@ map_single(struct device *hwdev, char *buffer, size_t size, int dir)
if (index >= io_tlb_nslabs)
index = 0;

- while (is_span_boundary(index, nslots, offset_slots,
- max_slots)) {
+ while (iommu_is_span_boundary(index, nslots, offset_slots,
+ max_slots)) {
index += stride;
if (index >= io_tlb_nslabs)
index = 0;
@@ -371,8 +363,9 @@ map_single(struct device *hwdev, char *buffer, size_t size, int dir)
index += stride;
if (index >= io_tlb_nslabs)
index = 0;
- } while (is_span_boundary(index, nslots, offset_slots,
- max_slots));
+ } while (iommu_is_span_boundary(index, nslots,
+ offset_slots,
+ max_slots));
} while (index != wrap);

spin_unlock_irqrestore(&io_tlb_lock, flags);
--
1.5.3.7


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