From: Will Deacon <will@kernel.org>
To: iommu@lists.linux-foundation.org
Cc: "Isaac J. Manjarres" <isaacm@codeaurora.org>,
Will Deacon <will@kernel.org>,
Robin Murphy <robin.murphy@arm.com>,
Pratik Patel <pratikp@codeaurora.org>,
linux-arm-kernel@lists.infradead.org
Subject: [RFC PATCH 3/6] iommu: Use bitmap to calculate page size in iommu_pgsize()
Date: Thu, 1 Apr 2021 17:47:35 +0100 [thread overview]
Message-ID: <20210401164738.9513-4-will@kernel.org> (raw)
In-Reply-To: <20210401164738.9513-1-will@kernel.org>
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().
Signed-off-by: Will Deacon <will@kernel.org>
---
drivers/iommu/iommu.c | 31 ++++++++++++-------------------
1 file changed, 12 insertions(+), 19 deletions(-)
diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
index d0b0a15dba84..bcd623862bf9 100644
--- a/drivers/iommu/iommu.c
+++ b/drivers/iommu/iommu.c
@@ -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>
@@ -2360,30 +2361,22 @@ 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);
- }
-
- /* build a mask of acceptable page sizes */
- pgsize = (1UL << (pgsize_idx + 1)) - 1;
-
- /* throw away page sizes not supported by the hardware */
- pgsize &= domain->pgsize_bitmap;
+ /* Constrain the page sizes further based on the maximum alignment */
+ if (likely(addr_merge))
+ pgsizes &= GENMASK(__ffs(addr_merge), 0);
- /* make sure we're still sane */
- BUG_ON(!pgsize);
+ /* Make sure we have at least one suitable page size */
+ BUG_ON(!pgsizes);
- /* 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;
}
--
2.31.0.291.g576ba9dcdaf-goog
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next prev parent reply other threads:[~2021-04-01 16:48 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-04-01 16:47 [RFC PATCH 0/6] iommu_pgsize() improvements to help towards ->[un]map_pages() Will Deacon
2021-04-01 16:47 ` [RFC PATCH 1/6] iommu/io-pgtable: Introduce unmap_pages() as a page table op Will Deacon
2021-04-01 16:47 ` [RFC PATCH 2/6] iommu: Add an unmap_pages() op for IOMMU drivers Will Deacon
2021-04-01 16:47 ` Will Deacon [this message]
2021-04-02 1:39 ` [RFC PATCH 3/6] iommu: Use bitmap to calculate page size in iommu_pgsize() isaacm
2021-04-06 11:40 ` Will Deacon
2021-04-01 16:47 ` [RFC PATCH 4/6] iommu: Split 'addr_merge' argument to iommu_pgsize() into separate parts Will Deacon
2021-04-01 16:47 ` [RFC PATCH 5/6] iommu: Hook up '->unmap_pages' driver callback Will Deacon
2021-04-01 16:47 ` [RFC PATCH 6/6] iommu: Accomodate larger pages in iommu_pgsize() 'count' calculation Will Deacon
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