linux-kernel - Re: [v2 PATCH] iommu/arm-smmu-v3: Fix L1 stream table index calculation for 32-bit sid size

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Message-ID: <20241004161408.GJ2456194@ziepe.ca>
Date: Fri, 4 Oct 2024 13:14:08 -0300
From: Jason Gunthorpe <jgg@...pe.ca>
To: Yang Shi <yang@...amperecomputing.com>
Cc: Nicolin Chen <nicolinc@...dia.com>, james.morse@....com,
	will@...nel.org, robin.murphy@....com,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [v2 PATCH] iommu/arm-smmu-v3: Fix L1 stream table index
 calculation for 32-bit sid size

On Fri, Oct 04, 2024 at 09:05:46AM -0700, Yang Shi wrote:
> 
> 
> On 10/4/24 5:43 AM, Jason Gunthorpe wrote:
> > On Thu, Oct 03, 2024 at 08:31:23AM -0700, Yang Shi wrote:
> > > If I understand correctly, the check is mainly used to avoid the u64 -> u32
> > > overflow. This check guarantee no overflow. If some crazy hardware really
> > > requests that large memory, the allocation will fail.
> > Sure, the kalloc will print a warn on anyhow if it is too big
> 
> Thank you. Will spin a new revision.

Oh wait a sec, it is not so simple, the 31 is too big because the
multiply will overflow or truncate to size_t too. This is why I picked
something lower.

Jason