From: isaacm@codeaurora.org
To: Will Deacon <will@kernel.org>
Cc: Robin Murphy <robin.murphy@arm.com>,
iommu@lists.linux-foundation.org,
Pratik Patel <pratikp@codeaurora.org>,
linux-arm-kernel@lists.infradead.org
Subject: Re: [RFC PATCH 3/6] iommu: Use bitmap to calculate page size in iommu_pgsize()
Date: Thu, 01 Apr 2021 18:39:35 -0700 [thread overview]
Message-ID: <7c012a63e8a5ad1856aac08995e6f154@codeaurora.org> (raw)
In-Reply-To: <20210401164738.9513-4-will@kernel.org>
On 2021-04-01 09:47, Will Deacon wrote:
> 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);
I've fixed this in the latest RFC for the iommu_map/unmap optimization
patches,
but for the sake of completeness: I think this should be GENMASK_ULL, in
case
__fls(size) >= 32.
Thank you for these patches, by the way. I've looked through them and
they
make sense/seem correct. I've integrated them into the latest RFC:
https://lore.kernel.org/linux-iommu/20210402013452.4013-1-isaacm@codeaurora.org/T/#t.
Thanks,
Isaac
>
> - /* 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;
> }
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next prev parent reply other threads:[~2021-04-02 1:39 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 ` [RFC PATCH 3/6] iommu: Use bitmap to calculate page size in iommu_pgsize() Will Deacon
2021-04-02 1:39 ` isaacm [this message]
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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