Re: [PATCH v3 4/7] iommu: Switch gather->end to unsigned long long

From: Robin Murphy
Date: Wed Dec 16 2020 - 07:11:13 EST


On 2020-12-16 10:36, Yong Wu wrote:
Currently gather->end is "unsigned long" which may be overflow in
arch32 in the corner case: 0xfff00000 + 0x100000(iova + size).
Although it doesn't affect the size(end - start), it affects the checking
"gather->end < end"

This won't help the same situation at the top of a 64-bit address space, though, and now that we have TTBR1 support for AArch64 format that is definitely a thing. Better to just encode the end address as the actual end address, i.e. iova + size - 1. We don't lose anything other than the ability to encode zero-sized invalidations that don't make sense anyway.

Robin.

Fixes: a7d20dc19d9e ("iommu: Introduce struct iommu_iotlb_gather for batching TLB flushes")
Signed-off-by: Yong Wu <yong.wu@xxxxxxxxxxxx>
---
include/linux/iommu.h | 5 +++--
1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/include/linux/iommu.h b/include/linux/iommu.h
index 794d4085edd3..6e907a95d981 100644
--- a/include/linux/iommu.h
+++ b/include/linux/iommu.h
@@ -178,7 +178,7 @@ enum iommu_dev_features {
*/
struct iommu_iotlb_gather {
unsigned long start;
- unsigned long end;
+ unsigned long long end;
size_t pgsize;
};
@@ -537,7 +537,8 @@ static inline void iommu_iotlb_gather_add_page(struct iommu_domain *domain,
struct iommu_iotlb_gather *gather,
unsigned long iova, size_t size)
{
- unsigned long start = iova, end = start + size;
+ unsigned long start = iova;
+ unsigned long long end = start + size;
/*
* If the new page is disjoint from the current range or is mapped at