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Date: Mon, 25 May 2020 07:24:18 +0000
From: Nicolas TOROMANOFF <nicolas.toromanoff@...com>
To: Ard Biesheuvel <ardb@...nel.org>
CC: Herbert Xu <herbert@...dor.apana.org.au>,
"David S . Miller" <davem@...emloft.net>,
Maxime Coquelin <mcoquelin.stm32@...il.com>,
"Alexandre TORGUE" <alexandre.torgue@...com>,
Linux Crypto Mailing List <linux-crypto@...r.kernel.org>,
"linux-stm32@...md-mailman.stormreply.com"
<linux-stm32@...md-mailman.stormreply.com>,
Linux ARM <linux-arm-kernel@...ts.infradead.org>,
Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH 5/5] crypto: stm32/crc: protect from concurrent accesses
Hello,
> -----Original Message-----
> From: Ard Biesheuvel <ardb@...nel.org>
> Sent: Friday, May 22, 2020 6:12 PM>
> On Tue, 12 May 2020 at 16:13, Nicolas Toromanoff
> <nicolas.toromanoff@...com> wrote:
> >
> > Protect STM32 CRC device from concurrent accesses.
> >
> > As we create a spinlocked section that increase with buffer size, we
> > provide a module parameter to release the pressure by splitting
> > critical section in chunks.
> >
> > Size of each chunk is defined in burst_size module parameter.
> > By default burst_size=0, i.e. don't split incoming buffer.
> >
> > Signed-off-by: Nicolas Toromanoff <nicolas.toromanoff@...com>
>
> Would you mind explaining the usage model here? It looks like you are sharing a
> CRC hardware accelerator with a synchronous interface between different users
> by using spinlocks? You are aware that this will tie up the waiting CPUs
> completely during this time, right? So it would be much better to use a mutex
> here. Or perhaps it would make more sense to fall back to a s/w based CRC
> routine if the h/w is tied up working for another task?
I know mutex are more acceptable here, but shash _update() and _init() may be call
from any context, and so I cannot take a mutex.
And to protect my concurrent HW access I only though about spinlock. Due to possible
constraint on CPUs, I add a burst_size option to force slitting long buffer into smaller one,
and so decrease time we take the lock.
But I didn't though to fallback to software CRC.
I'll do a patch on top.
In in the burst_update() function I'll use a spin_trylock_irqsave() and use software CRC32 if HW is already in use.
Thanks and regards,
Nicolas.
> Using spinlocks for this is really not acceptable.
>
>
>
> > ---
> > drivers/crypto/stm32/stm32-crc32.c | 47
> > ++++++++++++++++++++++++++++--
> > 1 file changed, 45 insertions(+), 2 deletions(-)
> >
> > diff --git a/drivers/crypto/stm32/stm32-crc32.c
> > b/drivers/crypto/stm32/stm32-crc32.c
> > index 413415c216ef..3ba41148c2a4 100644
> > --- a/drivers/crypto/stm32/stm32-crc32.c
> > +++ b/drivers/crypto/stm32/stm32-crc32.c
> > @@ -35,11 +35,16 @@
> >
> > #define CRC_AUTOSUSPEND_DELAY 50
> >
> > +static unsigned int burst_size;
> > +module_param(burst_size, uint, 0644); MODULE_PARM_DESC(burst_size,
> > +"Select burst byte size (0 unlimited)");
> > +
> > struct stm32_crc {
> > struct list_head list;
> > struct device *dev;
> > void __iomem *regs;
> > struct clk *clk;
> > + spinlock_t lock;
> > };
> >
> > struct stm32_crc_list {
> > @@ -109,6 +114,7 @@ static int stm32_crc_init(struct shash_desc *desc)
> > struct stm32_crc_desc_ctx *ctx = shash_desc_ctx(desc);
> > struct stm32_crc_ctx *mctx = crypto_shash_ctx(desc->tfm);
> > struct stm32_crc *crc;
> > + unsigned long flags;
> >
> > crc = stm32_crc_get_next_crc();
> > if (!crc)
> > @@ -116,6 +122,8 @@ static int stm32_crc_init(struct shash_desc *desc)
> >
> > pm_runtime_get_sync(crc->dev);
> >
> > + spin_lock_irqsave(&crc->lock, flags);
> > +
> > /* Reset, set key, poly and configure in bit reverse mode */
> > writel_relaxed(bitrev32(mctx->key), crc->regs + CRC_INIT);
> > writel_relaxed(bitrev32(mctx->poly), crc->regs + CRC_POL); @@
> > -125,18 +133,21 @@ static int stm32_crc_init(struct shash_desc *desc)
> > /* Store partial result */
> > ctx->partial = readl_relaxed(crc->regs + CRC_DR);
> >
> > + spin_unlock_irqrestore(&crc->lock, flags);
> > +
> > pm_runtime_mark_last_busy(crc->dev);
> > pm_runtime_put_autosuspend(crc->dev);
> >
> > return 0;
> > }
> >
> > -static int stm32_crc_update(struct shash_desc *desc, const u8 *d8,
> > - unsigned int length)
> > +static int burst_update(struct shash_desc *desc, const u8 *d8,
> > + size_t length)
> > {
> > struct stm32_crc_desc_ctx *ctx = shash_desc_ctx(desc);
> > struct stm32_crc_ctx *mctx = crypto_shash_ctx(desc->tfm);
> > struct stm32_crc *crc;
> > + unsigned long flags;
> >
> > crc = stm32_crc_get_next_crc();
> > if (!crc)
> > @@ -144,6 +155,8 @@ static int stm32_crc_update(struct shash_desc
> > *desc, const u8 *d8,
> >
> > pm_runtime_get_sync(crc->dev);
> >
> > + spin_lock_irqsave(&crc->lock, flags);
> > +
> > /*
> > * Restore previously calculated CRC for this context as init value
> > * Restore polynomial configuration @@ -182,12 +195,40 @@
> > static int stm32_crc_update(struct shash_desc *desc, const u8 *d8,
> > /* Store partial result */
> > ctx->partial = readl_relaxed(crc->regs + CRC_DR);
> >
> > + spin_unlock_irqrestore(&crc->lock, flags);
> > +
> > pm_runtime_mark_last_busy(crc->dev);
> > pm_runtime_put_autosuspend(crc->dev);
> >
> > return 0;
> > }
> >
> > +static int stm32_crc_update(struct shash_desc *desc, const u8 *d8,
> > + unsigned int length) {
> > + const unsigned int burst_sz = burst_size;
> > + unsigned int rem_sz;
> > + const u8 *cur;
> > + size_t size;
> > + int ret;
> > +
> > + if (!burst_sz)
> > + return burst_update(desc, d8, length);
> > +
> > + /* Digest first bytes not 32bit aligned at first pass in the loop */
> > + size = min(length,
> > + burst_sz + (unsigned int)d8 - ALIGN_DOWN((unsigned int)d8,
> > + sizeof(u32)));
> > + for (rem_sz = length, cur = d8; rem_sz;
> > + rem_sz -= size, cur += size, size = min(rem_sz, burst_sz)) {
> > + ret = burst_update(desc, cur, size);
> > + if (ret)
> > + return ret;
> > + }
> > +
> > + return 0;
> > +}
> > +
> > static int stm32_crc_final(struct shash_desc *desc, u8 *out) {
> > struct stm32_crc_desc_ctx *ctx = shash_desc_ctx(desc); @@
> > -300,6 +341,8 @@ static int stm32_crc_probe(struct platform_device *pdev)
> > pm_runtime_irq_safe(dev);
> > pm_runtime_enable(dev);
> >
> > + spin_lock_init(&crc->lock);
> > +
> > platform_set_drvdata(pdev, crc);
> >
> > spin_lock(&crc_list.lock);
> > --
> > 2.17.1
> >
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