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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

_______________________________________________
iommu mailing list
iommu@lists.linux-foundation.org
https://lists.linuxfoundation.org/mailman/listinfo/iommu

WARNING: multiple messages have this Message-ID (diff)
From: Will Deacon <will@kernel.org>
To: iommu@lists.linux-foundation.org
Cc: linux-arm-kernel@lists.infradead.org,
	Will Deacon <will@kernel.org>,
	"Isaac J. Manjarres" <isaacm@codeaurora.org>,
	Pratik Patel <pratikp@codeaurora.org>,
	Robin Murphy <robin.murphy@arm.com>,
	Lu Baolu <baolu.lu@linux.intel.com>
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


_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel

  parent reply	other threads:[~2021-04-01 16:48 UTC|newest]

Thread overview: 17+ 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 ` 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   ` 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
2021-04-01 16:47 ` Will Deacon [this message]
2021-04-01 16:47   ` [RFC PATCH 3/6] iommu: Use bitmap to calculate page size in iommu_pgsize() Will Deacon
2021-04-02  1:39   ` isaacm
2021-04-06 11:40     ` Will Deacon
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   ` 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   ` Will Deacon
2021-04-01 16:47 ` [RFC PATCH 6/6] iommu: Accomodate larger pages in iommu_pgsize() 'count' calculation Will Deacon
2021-04-01 16:47   ` Will Deacon

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