netdev - Re: [PATCH v8 0/7] Optimize dm-verity and fsverity using multibuffer hashing

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Message-ID: <Z7FblsbOQnJ7sYOA@gondor.apana.org.au>
Date: Sun, 16 Feb 2025 11:29:26 +0800
From: Herbert Xu <herbert@...dor.apana.org.au>
To: Eric Biggers <ebiggers@...nel.org>
Cc: Jakub Kicinski <kuba@...nel.org>, fsverity@...ts.linux.dev,
	linux-crypto@...r.kernel.org, dm-devel@...ts.linux.dev,
	x86@...nel.org, linux-arm-kernel@...ts.infradead.org,
	linux-kernel@...r.kernel.org, Ard Biesheuvel <ardb@...nel.org>,
	Sami Tolvanen <samitolvanen@...gle.com>,
	Alasdair Kergon <agk@...hat.com>, Mike Snitzer <snitzer@...nel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Mikulas Patocka <mpatocka@...hat.com>,
	David Howells <dhowells@...hat.com>, netdev@...r.kernel.org
Subject: Re: [PATCH v8 0/7] Optimize dm-verity and fsverity using multibuffer
 hashing

On Sat, Feb 15, 2025 at 07:26:16PM -0800, Eric Biggers wrote:
>
> Well, the async fallback (using cryptd) occurs only when a kernel-mode FPU
> section in process context is interrupted by a hardirq and at the end of it a
> softirq also tries to use kernel-mode FPU.  It's generally a rare case but also
> a terrible implementation that is really bad for performance; this should never

It may not be rare if the kernel is busy doing bidirectional
TX/RX with crypto.  The process context will be the TX-side
encrypting while the softirq context will do RX-side decryption.

> have been implemented this way.  I am planning to fix it so that softirqs on x86

Sure but it's way better than falling back to the C implementation
on the RX-side.

> will always be able to use the FPU, like they can on some of the other arches
> like arm64 and riscv.

That's great news.  Thanks!
-- 
Email: Herbert Xu <herbert@...dor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt