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Date: Mon, 06 Jul 2026 13:40:39 -1000
Message-ID: <205302f24c49036fea6afab94ea11ba5@kernel.org>
From: Tejun Heo <tj@kernel.org>
To: Andrea Righi <arighi@nvidia.com>
Cc: David Vernet <void@manifault.com>, Changwoo Min <changwoo@igalia.com>, sched-ext@lists.linux.dev, Emil Tsalapatis <emil@etsalapatis.com>, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2 sched_ext/for-7.3 15/36] sched_ext: Add scx_cmask_ref for validated arena cmask access
In-Reply-To: <aktvuGHVDEKnLlu5@gpd4>
References: <20260706014058.439853-1-tj@kernel.org> <20260706014058.439853-16-tj@kernel.org> <aktvuGHVDEKnLlu5@gpd4>
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Hi Andrea,

On Mon, 6 Jul 2026 11:04:56 +0200, Andrea Righi wrote:
> We validate the requested CID range, but not whether the cmask declares enough
> bits[] capacity for that range, unless I'm missing something. For example,
> nr_cids can require multiple words while alloc_words is one. Does the ref also
> need to account for the storage capacity described by alloc_words?

Right, that's a real gap - thanks. For v3, _init() also snapshots
alloc_words and rejects when SCX_CMASK_NR_WORDS(nr_cids) > alloc_words, so a
range that doesn't fit its declared storage is refused before any bits[]
access. I folded this into the patch together with dropping __counted_by,
which read the same BPF-writable count.

Thanks.