Received-SPF: pass (google.com: domain of linux-crypto-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
MIME-Version: 1.0
References: <20200420075711.2385190-1-Jason@zx2c4.com> <2cdb57f2cdbd49e9bb1034d01d054bb7@AcuMS.aculab.com>
In-Reply-To: <2cdb57f2cdbd49e9bb1034d01d054bb7@AcuMS.aculab.com>
From:   "Jason A. Donenfeld" <Jason@zx2c4.com>
Date:   Mon, 20 Apr 2020 22:02:31 -0600
Message-ID: <CAHmME9qfrHVQ+-4HjqCO2TaGF6DNTHmS1max1KcVaP5_QjUDRQ@mail.gmail.com>
Subject: Re: [PATCH crypto-stable] crypto: arch/lib - limit simd usage to
 PAGE_SIZE chunks
To:     David Laight <David.Laight@aculab.com>
Cc:     "herbert@gondor.apana.org.au" <herbert@gondor.apana.org.au>,
        "linux-crypto@vger.kernel.org" <linux-crypto@vger.kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "ebiggers@google.com" <ebiggers@google.com>,
        "ardb@kernel.org" <ardb@kernel.org>,
        "stable@vger.kernel.org" <stable@vger.kernel.org>
Content-Type: text/plain; charset="UTF-8"
Sender: linux-crypto-owner@vger.kernel.org
Precedence: bulk

On Mon, Apr 20, 2020 at 2:32 AM David Laight <David.Laight@aculab.com> wrote:
> Maybe kernel_fp_begin() should be passed the address of somewhere
> the address of an fpu save area buffer can be written to.
> Then the pre-emption code can allocate the buffer and save the
> state into it.
>
> However that doesn't solve the problem for non-preemptive kernels.
> The may need a cond_resched() in the loop if it might take 1ms (or so).
>
> kernel_fpu_begin() ought also be passed a parameter saying which
> fpu features are required, and return which are allocated.
> On x86 this could be used to check for AVX512 (etc) which may be
> available in an ISR unless it interrupted inside a kernel_fpu_begin()
> section (etc).
> It would also allow optimisations if only 1 or 2 fpu registers are
> needed (eg for some of the crypto functions) rather than the whole
> fpu register set.

There might be ways to improve lots of FPU things, indeed. This patch
here is just a patch to Herbert's branch in order to make uniform
usage of our existing solution for this, fixing the existing bug. I
wouldn't mind seeing more involved and better solutions in a patchset
for crypto-next.

Will follow up with your suggestion in a different thread, so as not
to block this one.