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FROMLIST: iommu: Use bitmap to calculate page size in iommu_pgsize()

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Avoid the potential for shifting values by amounts greater than the
width of their type by using a bitmap to compute page size in
iommu_pgsize().

Bug: 178537788
Change-Id: I5beb1beb3ca7d412244180114c96c34e52b74d1c
Link: https://lore.kernel.org/linux-iommu/20210408171402.12607-1-isaacm@codeaurora.org/T/#t
Signed-off-by: Will Deacon <will@kernel.org>
Signed-off-by: Isaac J. Manjarres <isaacm@codeaurora.org>
This commit is contained in:
Will Deacon
2021-04-01 17:47:35 +01:00
committed by Todd Kjos
parent 16cabf65c7
commit 35dde30a45
1 changed files with 12 additions and 19 deletions
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31
drivers/iommu/iommu.c
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@@ -8,6 +8,7 @@
#include <linux/device.h>
#include <linux/kernel.h>
#include <linux/bits.h>
#include <linux/bug.h>
#include <linux/types.h>
#include <linux/init.h>
@@ -2333,30 +2334,22 @@ static size_t iommu_pgsize(struct iommu_domain *domain,
unsigned long addr_merge, size_t size)
{
unsigned int pgsize_idx;
unsigned long pgsizes;
size_t pgsize;
/* Max page size that still fits into 'size' */
pgsize_idx = __fls(size);
/* Page sizes supported by the hardware and small enough for @size */
pgsizes = domain->pgsize_bitmap & GENMASK(__fls(size), 0);
/* need to consider alignment requirements ? */
if (likely(addr_merge)) {
/* Max page size allowed by address */
unsigned int align_pgsize_idx = __ffs(addr_merge);
pgsize_idx = min(pgsize_idx, align_pgsize_idx);
}
/* Constrain the page sizes further based on the maximum alignment */
if (likely(addr_merge))
pgsizes &= GENMASK(__ffs(addr_merge), 0);
/* build a mask of acceptable page sizes */
pgsize = (1UL << (pgsize_idx + 1)) - 1;
/* Make sure we have at least one suitable page size */
BUG_ON(!pgsizes);
/* throw away page sizes not supported by the hardware */
pgsize &= domain->pgsize_bitmap;
/* make sure we're still sane */
BUG_ON(!pgsize);
/* pick the biggest page */
pgsize_idx = __fls(pgsize);
pgsize = 1UL << pgsize_idx;
/* Pick the biggest page size remaining */
pgsize_idx = __fls(pgsizes);
pgsize = BIT(pgsize_idx);
return pgsize;
}