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Date:   Wed, 11 Apr 2018 10:08:06 +0200
From:   Boris Brezillon <boris.brezillon@bootlin.com>
To:     Ladislav Michl <ladis@linux-mips.org>
Cc:     Andreas Kemnade <andreas@kemnade.info>,
        Discussions about the Letux Kernel 
        <letux-kernel@openphoenux.org>,
        Boris Brezillon <boris.brezillon@free-electrons.com>,
        Aaro Koskinen <aaro.koskinen@iki.fi>,
        Tony Lindgren <tony@atomide.com>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Peter Ujfalusi <peter.ujfalusi@ti.com>,
        linux-omap <linux-omap@vger.kernel.org>,
        Roger Quadros <rogerq@ti.com>
Subject: Re: [Letux-kernel] [Bug]: mtd: onenand: omap2plus: kernel panic
 with OneNAND on OMAP3 (DM3730) device GTA04A5
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        <20180411073655.GA18273@lenoch>
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On Wed, 11 Apr 2018 09:36:56 +0200
Ladislav Michl <ladis@linux-mips.org> wrote:

> Hi Boris,
> 
> On Wed, Apr 11, 2018 at 09:15:28AM +0200, Boris Brezillon wrote:
> > Hi Ladislav,
> > 
> > On Wed, 11 Apr 2018 08:26:07 +0200
> > Ladislav Michl <ladis@linux-mips.org> wrote:
> >   
> > > Hi Andreas,
> > > 
> > > On Wed, Apr 11, 2018 at 06:59:03AM +0200, Andreas Kemnade wrote:  
> > > > Hi Ladis,
> > > > 
> > > > On Tue, 10 Apr 2018 22:56:43 +0200
> > > > Ladislav Michl <ladis@linux-mips.org> wrote:
> > > >     
> > > > > Hi Nikolaus,
> > > > > 
> > > > > On Tue, Apr 10, 2018 at 06:25:17PM +0200, H. Nikolaus Schaller wrote:    
> > > > > > Hi,
> > > > > > we just started testing the v4.16 kernel and found the
> > > > > > device no longer bootable (works with v4.15). It turned
> > > > > > out that there was a harmful modification somewhere between
> > > > > > v4.15.0 and v4.16-rc1.
> > > > > > 
> > > > > > A git bisect points to this patch:      
> > > > > 
> > > > > Well, that's a shame... However, this code is in production for several
> > > > > months now, so could you, please put 'goto out_copy' if 'buf >= high_memory'
> > > > > condition is met, ie:
> > > > > --- a/drivers/mtd/nand/onenand/omap2.c
> > > > > +++ b/drivers/mtd/nand/onenand/omap2.c
> > > > > @@ -392,6 +392,7 @@ static int omap2_onenand_read_bufferram(struct mtd_info *mtd, int area,
> > > > >  	if (buf >= high_memory) {
> > > > >  		struct page *p1;
> > > > >  
> > > > > +		goto out_copy;
> > > > >  		if (((size_t)buf & PAGE_MASK) !=
> > > > >  		    ((size_t)(buf + count - 1) & PAGE_MASK))
> > > > >  			goto out_copy;    
> > > > 
> > > > I had the same problem here, and that snippet  helps here. ubiattach
> > > > -p /dev/mtdX does not cause kernel oopses here anymore    
> > > 
> > > It seems reviving old code always comes at a price :-) Could you try
> > > following patch, so far compile tested only?
> > > (we'll need to do the same for omap2_onenand_write_bufferram, but
> > > it sould be enough for testing purposes now)
> > > 
> > > diff --git a/drivers/mtd/nand/onenand/omap2.c b/drivers/mtd/nand/onenand/omap2.c
> > > index 9c159f0dd9a6..04cefd7a6487 100644
> > > --- a/drivers/mtd/nand/onenand/omap2.c
> > > +++ b/drivers/mtd/nand/onenand/omap2.c
> > > @@ -375,11 +375,12 @@ static int omap2_onenand_read_bufferram(struct mtd_info *mtd, int area,
> > >  {
> > >  	struct omap2_onenand *c = container_of(mtd, struct omap2_onenand, mtd);
> > >  	struct onenand_chip *this = mtd->priv;
> > > +	struct device *dev = &c->pdev->dev;
> > >  	dma_addr_t dma_src, dma_dst;
> > >  	int bram_offset;
> > >  	void *buf = (void *)buffer;
> > >  	size_t xtra;
> > > -	int ret;
> > > +	int ret, page_dma = 0;
> > >  
> > >  	bram_offset = omap2_onenand_bufferram_offset(mtd, area) + area + offset;
> > >  	if (bram_offset & 3 || (size_t)buf & 3 || count < 384)
> > > @@ -389,38 +390,43 @@ static int omap2_onenand_read_bufferram(struct mtd_info *mtd, int area,
> > >  	if (in_interrupt() || oops_in_progress)
> > >  		goto out_copy;
> > >  
> > > +	xtra = count & 3;
> > > +	if (xtra) {
> > > +		count -= xtra;
> > > +		memcpy(buf + count, this->base + bram_offset + count, xtra);
> > > +	}
> > > +
> > > +	/* Handle vmalloc address */
> > >  	if (buf >= high_memory) {
> > > -		struct page *p1;
> > > +		struct page *page;
> > >  
> > >  		if (((size_t)buf & PAGE_MASK) !=
> > >  		    ((size_t)(buf + count - 1) & PAGE_MASK))
> > >  			goto out_copy;
> > > -		p1 = vmalloc_to_page(buf);
> > > -		if (!p1)
> > > +		page = vmalloc_to_page(buf);  
> > 
> > Not sure this approach is safe on all archs: if the cache is VIVT or
> > VIPT, you may have several entries pointing to the same phys page, and
> > then, when dma_map_page() does its cache maintenance operations, it's
> > only taking one of these entries into account.  
> 
> Hmm, I used the same approach Samsung OneNAND driver does since commit
> dcf08227e964a53a2cb39130b74842c7dcb6adde.
> Both TI OMAP3630 and Samsung S5PC110 are using Cortex-A8 which
> is VIPT. In that case samsung's driver code has the same problem.
> 
> > In other parts of the MTD subsystem, we tend to not do DMA on buffers
> > that have been vmalloc-ed.
> > 
> > You can do something like
> > 
> > 		if (virt_addr_valid(buf))
> > 			/* Use DMA */
> > 		else
> > 			/*
> > 			 * Do not use DMA, or use a bounce buffer
> > 			 * allocated with kmalloc
> > 			 */  
> 
> Okay, I'll use this approach then, but first I'd like to be sure above is
> correct. Anyone?

See this discussion [1]. The problem came up a few times already, so
might find other threads describing why it's not safe.

[1]https://lists.linuxfoundation.org/pipermail/iommu/2016-March/016240.html