linux-kernel - Re: scatterlist: sg_set_buf() argument must be in linear mapping (sha1: ac4e97abce9b80c020e7113325f49e58b7b15e3f)

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Message-ID: <87ppua9feh.fsf@rustcorp.com.au>
Date:	Tue, 23 Jul 2013 12:00:30 +0930
From:	Rusty Russell <rusty@...tcorp.com.au>
To:	monstr@...str.eu
Cc:	Jens Axboe <axboe@...nel.dk>, LKML <linux-kernel@...r.kernel.org>,
	Ohad Ben-Cohen <ohad@...ery.com>,
	Russell King <linux@....linux.org.uk>,
	linux-arm-kernel@...ts.infradead.org
Subject: Re: scatterlist: sg_set_buf() argument must be in linear mapping (sha1: ac4e97abce9b80c020e7113325f49e58b7b15e3f)

Michal Simek <monstr@...str.eu> writes:
> + Ohad
>
> On 07/22/2013 03:47 AM, Rusty Russell wrote:
>> Michal Simek <monstr@...str.eu> writes:
>>> Hi Rusty and Jens,
>>>
>>> I am getting problem with your patch which you have added to the kernel.
>>> The problem is with my arm zynq remoteproc driver where
>>> I use dma_declare_coherent_memory() to specify memory for remoteproc
>>> which is ioremap to the vmalloc area.
>>>
>>> Based on that buf addr is not inside ram even this coherent memory is in ram.
>>> That's why virt_addr_valid(buf) is failing.
>> 
>> But sg_set_buf() calls virt_to_page(buf).  So does that work?
>> 
>> I would think calling sg_set_page() directly would be what you want
>> here...
>
> Let me take some code from virtio_rpmsg_bus.c to show that problematic part.
>
> bufs_va = dma_alloc_coherent(vdev->dev.parent->parent,
> 				RPMSG_TOTAL_BUF_SPACE,
> 				&vrp->bufs_dma, GFP_KERNEL);
> vrp->rbufs = bufs_va;
> for (i = 0; i < RPMSG_NUM_BUFS / 2; i++) {
> 	struct scatterlist sg;
> 	void *cpu_addr = vrp->rbufs + i * RPMSG_BUF_SIZE;
>
> 	sg_init_one(&sg, cpu_addr, RPMSG_BUF_SIZE);
> }

Hmm.  Looking at arch/arm/include/asm/memory.h:

#define virt_to_page(kaddr)	pfn_to_page(__pa(kaddr) >> PAGE_SHIFT)
#define virt_addr_valid(kaddr)	((unsigned long)(kaddr) >= PAGE_OFFSET && (unsigned long)(kaddr) < (unsigned long)high_memory)

pfn_to_page in ARM seems to be the asm-generic one, which depends on
CONFIG_SPARSEMEM/CONFIG_DISCONTIGMEM/CONFIG_FLATMEM etc.

Perhaps virt_addr_valid() is wrong for your config?  It's pretty clear
that you shouldn't call virt_to_page() on something for which
!virt_addr_valid().

Cheers,
Rusty.
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