linux-kernel - Re: [PATCH v10 0/5] Introduce mseal

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Message-ID: <CAKbZUD1ZLfAPznGg-j2xmC7O2a-b8jRRQjSgRLRUrP8DQ6Lntg@mail.gmail.com>
Date: Fri, 19 Apr 2024 18:59:20 +0100
From: Pedro Falcato <pedro.falcato@...il.com>
To: Jeff Xu <jeffxu@...omium.org>
Cc: Suren Baghdasaryan <surenb@...gle.com>, "Liam R. Howlett" <Liam.Howlett@...cle.com>, 
	akpm@...ux-foundation.org, keescook@...omium.org, jannh@...gle.com, 
	sroettger@...gle.com, willy@...radead.org, gregkh@...uxfoundation.org, 
	torvalds@...ux-foundation.org, usama.anjum@...labora.com, corbet@....net, 
	merimus@...gle.com, rdunlap@...radead.org, jeffxu@...gle.com, 
	jorgelo@...omium.org, groeck@...omium.org, linux-kernel@...r.kernel.org, 
	linux-kselftest@...r.kernel.org, linux-mm@...ck.org, dave.hansen@...el.com, 
	linux-hardening@...r.kernel.org, deraadt@...nbsd.org
Subject: Re: [PATCH v10 0/5] Introduce mseal

On Fri, Apr 19, 2024 at 2:22 AM Jeff Xu <jeffxu@...omium.org> wrote:
> The overhead is likely to grow linearly with the number of VMA, since
> it takes time to retrieve VMA's metadata.
>
> Let's use one data sample to look at impact:
>
> Test: munmap 1000 memory range, each memory range has 1 VMA
>
> syscall__       vmas    t       t_mseal delta_ns        per_vma %
> munmap__        1       909     944     35      35      104%
>
> For those 1000 munmap calls, sealing adds 35000 ns in total, or 35 ns per call.

Have you tried to spray around some likely() and unlikely()s? Does
that make a difference? I'm thinking that sealing VMAs will be very
rare, and mprotect/munmapping them is probably a programming error
anyway, so the extra branches in the mprotect/munmap/madvice (etc)
should be a nice target for some branch annotation.

-- 
Pedro