From: Maxime Ripard Subject: Re: [PATCH] crypto: sun4i-ss: prevent deadlock on emulated hardware Date: Fri, 15 Jun 2018 11:04:12 +0200 Message-ID: <20180615090412.xgw35ga5cvc6w3h3@flea> References: <20180614193659.29261-1-clabbe.montjoie@gmail.com> <20180615075754.b3ivyagjsomiafwk@flea> <20180615081554.GA3047@Red> Reply-To: maxime.ripard-LDxbnhwyfcJBDgjK7y7TUQ@public.gmane.org Mime-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="2mo5zrs2piu4jjwq" Cc: davem-fT/PcQaiUtIeIZ0/mPfg9Q@public.gmane.org, herbert-lOAM2aK0SrRLBo1qDEOMRrpzq4S04n8Q@public.gmane.org, wens-jdAy2FN1RRM@public.gmane.org, linux-arm-kernel-IAPFreCvJWM7uuMidbF8XUB+6BGkLq7r@public.gmane.org, linux-crypto-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-sunxi-/JYPxA39Uh5TLH3MbocFFw@public.gmane.org To: Corentin Labbe Return-path: Sender: linux-sunxi-/JYPxA39Uh5TLH3MbocFFw@public.gmane.org Content-Disposition: inline In-Reply-To: <20180615081554.GA3047@Red> List-Post: , List-Help: , List-Archive: , List-Unsubscribe: , List-Id: linux-crypto.vger.kernel.org --2mo5zrs2piu4jjwq Content-Type: text/plain; charset="UTF-8" Content-Disposition: inline On Fri, Jun 15, 2018 at 10:15:54AM +0200, Corentin Labbe wrote: > On Fri, Jun 15, 2018 at 09:57:54AM +0200, Maxime Ripard wrote: > > On Thu, Jun 14, 2018 at 09:36:59PM +0200, Corentin Labbe wrote: > > > Running a qemu emulated cubieboard with sun4i-ss driver enabled led to a never > > > ending boot. > > > This is due to sun4i-ss deadlocked and taking all cpu in an infinite loop. > > > Since the crypto hardware is not implemented, all registers are read as 0. > > > So sun4i-ss will never progress in any operations. (TX_CNT being always 0) > > > > > > The first idea is to add a "TX_CNT always zero timeout" but this made cipher/hash loops > > > more complex and prevent a case that never happen on real hardware. > > > > > > The best way to fix is to check at probe time if we run on a virtual > > > machine with hardware emulated but non-implemented and prevent > > > sun4i-ss to be loaded in that case. > > > Letting sun4i-ss to load is useless anyway since all crypto algorithm will be > > > disabled since they will fail crypto selftests. > > > > > > Tested-on: qemu-cubieboard > > > Tested-on: cubieboard2 > > > > > > Signed-off-by: Corentin Labbe > > > --- > > > drivers/crypto/sunxi-ss/sun4i-ss-core.c | 10 ++++++++++ > > > 1 file changed, 10 insertions(+) > > > > > > diff --git a/drivers/crypto/sunxi-ss/sun4i-ss-core.c b/drivers/crypto/sunxi-ss/sun4i-ss-core.c > > > index a81d89b3b7d8..a178e80adcf3 100644 > > > --- a/drivers/crypto/sunxi-ss/sun4i-ss-core.c > > > +++ b/drivers/crypto/sunxi-ss/sun4i-ss-core.c > > > @@ -341,9 +341,18 @@ static int sun4i_ss_probe(struct platform_device *pdev) > > > * I expect to be a sort of Security System Revision number. > > > * Since the A80 seems to have an other version of SS > > > * this info could be useful > > > + * Detect virtual machine with non-implemented hardware > > > + * (qemu-cubieboard) by checking the register value after a write to it. > > > + * On non-implemented hardware, all registers are read as 0. > > > + * On real hardware we should have a value > 0. > > > */ > > > writel(SS_ENABLED, ss->base + SS_CTL); > > > v = readl(ss->base + SS_CTL); > > > + if (!v) { > > > + dev_err(&pdev->dev, "Qemu with non-implemented SS detected.\n"); > > > + err = -ENODEV; > > > + goto error_rst; > > > + } > > > > This is wrong way to tackle the issue. There's multiple reason why > > this could happen (for example the device not being clocked, or > > maintained in reset). There's nothing specific about qemu here, and > > the fundamental issue isn't that the device isn't functional in qemu, > > it's that qemu lies about which hardware it can emulate in the DT it > > passes to the kernel. > > > > There's no way this can scale, alone from the fact that qemu should > > patch the DT according to what it can do. Not trying to chase after > > each and every device that is broken in qemu. > > > > NAK. > > > > My fix detect also when the device is badly clocked. In which case, the proper fix is to enable the clock, not throw the kernel's arm up in the air. Maxime -- Maxime Ripard, Bootlin (formerly Free Electrons) Embedded Linux and Kernel engineering https://bootlin.com --2mo5zrs2piu4jjwq--