From: Rasmus Villemoes <linux@rasmusvillemoes.dk>
To: Suren Baghdasaryan <surenb@google.com>, akpm@linux-foundation.org
Cc: ccross@google.com, sumit.semwal@linaro.org, mhocko@suse.com,
dave.hansen@intel.com, keescook@chromium.org,
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vbabka@suse.cz, hannes@cmpxchg.org, corbet@lwn.net,
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linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org,
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kernel-team@android.com
Subject: Re: [PATCH v9 2/3] mm: add a field to store names for private anonymous memory
Date: Fri, 1 Oct 2021 09:01:23 +0200 [thread overview]
Message-ID: <d8619a98-2380-ca96-001e-60fe9c6204a6@rasmusvillemoes.dk> (raw)
In-Reply-To: <20210902231813.3597709-2-surenb@google.com>
On 03/09/2021 01.18, Suren Baghdasaryan wrote:
> From: Colin Cross <ccross@google.com>
>
>
> changes in v9
> - Changed max anon vma name length from 64 to 256 (as in the original patch)
> because I found one case of the name length being 139 bytes. If anyone is
> curious, here it is:
> dalvik-/data/dalvik-cache/arm64/apex@com.android.permission@priv-app@GooglePermissionController@GooglePermissionController.apk@classes.art
I'm not sure that's a very convincing argument. We don't add code
arbitrarily just because some userspace code running on some custom
kernel (ab)uses something in that kernel. Surely that user can come up
with a name that doesn't contain GooglePermissionController twice.
The argument for using strings and not just a 128 bit uuid was that it
should (also) be human readable, and 250-byte strings are not that.
Also, there's no natural law forcing this to be some power-of-two, and
in fact the implementation means that it's actually somewhat harmful
(give it a 256 char name, and we'll do a 260 byte alloc, which becomes a
512 byte alloc). So just make the limit 80, the kernel's definition of a
sane line length. As for the allowed chars, it can be relaxed later if
convincing arguments can be made.
> +/* mmap_lock should be read-locked */
> +static inline bool is_same_vma_anon_name(struct vm_area_struct *vma,
> + const char *name)
> +{
> + const char *vma_name = vma_anon_name(vma);
> +
> + if (likely(!vma_name))
> + return name == NULL;
> +
> + return name && !strcmp(name, vma_name);
It's probably preferable to spell this
/* either both NULL, or pointers to same refcounted string */
if (vma_name == name)
return true;
return name && vma_name && !strcmp(name, vma_name);
so you have one less conditional in the common case.
Rasmus
next prev parent reply other threads:[~2021-10-01 7:01 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-09-02 23:18 [PATCH v9 1/3] mm: rearrange madvise code to allow for reuse Suren Baghdasaryan
2021-09-02 23:18 ` [PATCH v9 2/3] mm: add a field to store names for private anonymous memory Suren Baghdasaryan
2021-09-03 21:35 ` Kees Cook
2021-09-03 21:51 ` Suren Baghdasaryan
2021-09-05 13:04 ` Pavel Machek
2021-09-06 15:52 ` Suren Baghdasaryan
2021-09-03 21:47 ` Kees Cook
2021-09-03 21:56 ` Suren Baghdasaryan
2021-09-03 22:28 ` Kees Cook
2021-10-01 3:44 ` Suren Baghdasaryan
2021-10-01 5:19 ` Kees Cook
2021-09-06 16:55 ` Matthew Wilcox
2021-09-09 4:05 ` Suren Baghdasaryan
2021-09-30 18:56 ` Suren Baghdasaryan
2021-09-30 23:25 ` Kees Cook
2021-10-01 7:01 ` Rasmus Villemoes [this message]
2021-10-01 16:34 ` Suren Baghdasaryan
2021-09-02 23:18 ` [PATCH v9 3/3] mm: add anonymous vma name refcounting Suren Baghdasaryan
2021-09-03 22:20 ` Kees Cook
2021-09-03 0:28 ` [PATCH v9 1/3] mm: rearrange madvise code to allow for reuse Suren Baghdasaryan
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