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SubjectRe: mm/percpu.c: use smarter memory allocation for struct pcpu_alloc_info (crisv32 hang)
On Wed, Nov 22, 2017 at 03:17:00PM -0500, Nicolas Pitre wrote:
> On Wed, 22 Nov 2017, Jesper Nilsson wrote:
>
> > On Mon, Nov 20, 2017 at 10:50:46PM -0500, Nicolas Pitre wrote:
> > > On Mon, 20 Nov 2017, Guenter Roeck wrote:
> > > > On Mon, Nov 20, 2017 at 07:28:21PM -0500, Nicolas Pitre wrote:
> > > > > On Mon, 20 Nov 2017, Guenter Roeck wrote:
> > > > >
> > > > > > bdata->node_min_pfn=60000 PFN_PHYS(bdata->node_min_pfn)=c0000000 start_off=536000 region=c0536000
> > > > >
> > > > > If PFN_PHYS(bdata->node_min_pfn)=c0000000 and
> > > > > region=c0536000 that means phys_to_virt() is a no-op.
> > > > >
> > > > No, it is |= 0x80000000
> > >
> > > Then the bootmem registration looks very fishy. If you have:
> > >
> > > > I think the problem is the 0x60000 in bdata->node_min_pfn. It is shifted
> > > > left by PFN_PHYS, making it 0xc0000000, which in my understanding is
> > > > a virtual address.
> > >
> > > Exact.
> > >
> > > #define __pa(x) ((unsigned long)(x) & 0x7fffffff)
> > > #define __va(x) ((void *)((unsigned long)(x) | 0x80000000))
> > >
> > > With that, the only possible physical address range you may have is
> > > 0x40000000 - 0x7fffffff, and it better start at 0x40000000. If that's
> > > not where your RAM is then something is wrong.
> > >
> > > This is in fact a very bad idea to define __va() and __pa() using
> > > bitwise operations as this hides mistakes like defining physical RAM
> > > address at 0xc0000000. Instead, it should look like:
> > >
> > > #define __pa(x) ((unsigned long)(x) - 0x80000000)
> > > #define __va(x) ((void *)((unsigned long)(x) + 0x80000000))
> > >
> > > This way, bad physical RAM address definitions will be caught
> > > immediately.
> > >
> > > > That doesn't seem to be easy to fix. It seems there is a mixup of physical
> > > > and virtual addresses in the architecture.
> > >
> > > Well... I don't think there is much else to say other than this needs
> > > fixing.
> >
> > The memory map for the ETRAX FS has the SDRAM mapped at both 0x40000000-0x7fffffff
> > and 0xc0000000-0xffffffff, and the difference is cached and non-cached.
> > That is actively (ab)used in the port, unfortunately, allthough I'm
> > uncertain if this is the problem in this case.
>
> It certainly is a problem. If your cached RAM is physically mapped at
> 0xc0000000 and you want it to be virtually mapped at 0xc0000000 then you
> should have:
>
> #define __pa(x) ((unsigned long)(x))
> #define __va(x) ((void *)(x))
>
> i.e. no translation.

Sorry, it's the other way around, cached memory is at 0x40000000 and
non-cached is at 0xc0000000, so the translation is right, even if
as you pointed out earlier, it should be performed differently.

> For non-cached RAM access, there are specific
> interfaces for that. For example, you could have dma_alloc_coherent()
> take advantage of the fact that memory with the top bit cleared becomes
> uncached. But __pa() is the wrong interface for obtaining uncached
> memory.
>
> Nicolas

/^JN - Jesper Nilsson
--
Jesper Nilsson -- jesper.nilsson@axis.com

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