From: Will Deacon <will@kernel.org>
To: isaacm@codeaurora.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: Tue, 6 Apr 2021 12:40:32 +0100 [thread overview]
Message-ID: <20210406114032.GA13747@willie-the-truck> (raw)
In-Reply-To: <7c012a63e8a5ad1856aac08995e6f154@codeaurora.org>
On Thu, Apr 01, 2021 at 06:39:35PM -0700, isaacm@codeaurora.org wrote:
> 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.
Hmm, but 'size' is a size_t; which architectures have sizeof(size_t) >
sizeof(unsigned long)?
> > - /* 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);
This one looks like more of an issue, though, as addr_merge is a
phys_addr_t, which certainly can be 64-bit where unsigned long is 32-bit
(e.g. Armv7 + LPAE)
Rather than make everything _ULL, please can you just do it where we're
actually using the larger types?
Will
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next prev parent reply other threads:[~2021-04-06 11:40 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
2021-04-06 11:40 ` Will Deacon [this message]
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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