usb zero copy dma handling
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Message ID 20190808084636.GB15080@priv-mua.localdomain
State New
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  • usb zero copy dma handling
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Commit Message

yvahkhfo.1df7f8c2@hashmail.org Aug. 8, 2019, 8:46 a.m. UTC
Hello linux-usb and linux-arm.

Ccing security@ because "the kernel dma code is mapping randomish
kernel/user mem to a user process" seems to have security implications
even though i didnt research that aspect past "its a 100% reliable way
to crash a raspi from userspace". 

tried submitting this through linux-arm-kernel ~2 weeks ago but
the only "response" i got was phishing-spam.
tried to follow up through raspi-internals chat, they suggested
i try linux-usb instead, but otoh the original reporter was
deflected from -usb to "try some other mls, they might care".
https://www.spinics.net/lists/linux-usb/msg173277.html

if i am not following some arcane ritual or indenting convention required 
by regular users of these lists i apologize in advance, but i am not a 
kernel developer, i am just here as a user with a bug and a patch. 
(and the vger FAQ link 404s...) 

i rediffed against HEAD even though the two weeks old patch still applied
cleanly with +2 offset.

# stepping off soap box # actual technical content starts here #

this is a followup to that thread from 2018-11:
https://www.spinics.net/lists/arm-kernel/msg685598.html

the issue was discussed in more detail than i can claim
to fully understand back then, but no fix ever merged.
but i would really like to use rtl_433 on a raspi without
having to build a custom-patched kernel first.

the attached patch is my stripdown/cleanup of a devel-diff
provided to me by the original reporter Steve Markgraf.
credits to him for the good parts, blame to me for the bad parts.

this does not cover the additional case of "PIO-based usb controllers"
mainly because i dont understand what that means (or how to handle it)
and if its broken right now (as the thread indicates) it might
as well stay broken until someone who understands cares enough.

could you please get this on track for merging?

regards,
  x23

Comments

Greg KH Aug. 8, 2019, 8:58 a.m. UTC | #1
On Thu, Aug 08, 2019 at 10:46:36AM +0200, yvahkhfo.1df7f8c2@hashmail.org wrote:
> Hello linux-usb and linux-arm.
> 
> Ccing security@ because "the kernel dma code is mapping randomish
> kernel/user mem to a user process" seems to have security implications
> even though i didnt research that aspect past "its a 100% reliable way
> to crash a raspi from userspace". 
> 
> tried submitting this through linux-arm-kernel ~2 weeks ago but
> the only "response" i got was phishing-spam.
> tried to follow up through raspi-internals chat, they suggested
> i try linux-usb instead, but otoh the original reporter was
> deflected from -usb to "try some other mls, they might care".
> https://www.spinics.net/lists/linux-usb/msg173277.html
> 
> if i am not following some arcane ritual or indenting convention required 
> by regular users of these lists i apologize in advance, but i am not a 
> kernel developer, i am just here as a user with a bug and a patch. 
> (and the vger FAQ link 404s...) 

The "arcane ritual" should be really well documented by now, it's in
Documentation/SubmittingPatches in your kernel tree, and you can read it
online at:
	https://www.kernel.org/doc/html/latest/process/submitting-patches.html


> i rediffed against HEAD even though the two weeks old patch still applied
> cleanly with +2 offset.
> 
> # stepping off soap box # actual technical content starts here #
> 
> this is a followup to that thread from 2018-11:
> https://www.spinics.net/lists/arm-kernel/msg685598.html
> 
> the issue was discussed in more detail than i can claim
> to fully understand back then, but no fix ever merged.
> but i would really like to use rtl_433 on a raspi without
> having to build a custom-patched kernel first.
> 
> the attached patch is my stripdown/cleanup of a devel-diff
> provided to me by the original reporter Steve Markgraf.
> credits to him for the good parts, blame to me for the bad parts.
> 
> this does not cover the additional case of "PIO-based usb controllers"
> mainly because i dont understand what that means (or how to handle it)
> and if its broken right now (as the thread indicates) it might
> as well stay broken until someone who understands cares enough.
> 
> could you please get this on track for merging?


> 
> regards,
>   x23
> 
> 
> 

> diff --git a/drivers/usb/core/devio.c b/drivers/usb/core/devio.c
> index b265ab5405f9..69594c2169ea 100644
> --- a/drivers/usb/core/devio.c
> +++ b/drivers/usb/core/devio.c
> @@ -238,9 +238,14 @@ static int usbdev_mmap(struct file *file, struct vm_area_struct *vma)
>  	usbm->vma_use_count = 1;
>  	INIT_LIST_HEAD(&usbm->memlist);
>  
> +#ifdef CONFIG_X86
>  	if (remap_pfn_range(vma, vma->vm_start,
>  			virt_to_phys(usbm->mem) >> PAGE_SHIFT,
>  			size, vma->vm_page_prot) < 0) {
> +#else /* !CONFIG_X86 */
> +	if (dma_mmap_coherent(ps->dev->bus->sysdev, 
> +			vma, mem, dma_handle, size) < 0) {
> +#endif /* !CONFIG_X86 */
>  		dec_usb_memory_use_count(usbm, &usbm->vma_use_count);
>  		return -EAGAIN;
>  	}

First off, we need this in a format we could apply it in (hint, read the
above links).

But the main issue here is what exactly is this "fixing"?  What is wrong
with the existing code that non-x86 systems have such a problem with?
Shouldn't all of these dma issues be handled by the platform with the
remap_pfn_range() call itself?

What is the problem that you are having?

thanks,

greg k-h
Robin Murphy Aug. 8, 2019, 9:46 a.m. UTC | #2
On 2019-08-08 9:58 am, Greg KH wrote:
> On Thu, Aug 08, 2019 at 10:46:36AM +0200, yvahkhfo.1df7f8c2@hashmail.org wrote:
>> Hello linux-usb and linux-arm.
>>
>> Ccing security@ because "the kernel dma code is mapping randomish
>> kernel/user mem to a user process" seems to have security implications
>> even though i didnt research that aspect past "its a 100% reliable way
>> to crash a raspi from userspace".
>>
>> tried submitting this through linux-arm-kernel ~2 weeks ago but
>> the only "response" i got was phishing-spam.
>> tried to follow up through raspi-internals chat, they suggested
>> i try linux-usb instead, but otoh the original reporter was
>> deflected from -usb to "try some other mls, they might care".
>> https://www.spinics.net/lists/linux-usb/msg173277.html
>>
>> if i am not following some arcane ritual or indenting convention required
>> by regular users of these lists i apologize in advance, but i am not a
>> kernel developer, i am just here as a user with a bug and a patch.
>> (and the vger FAQ link 404s...)
> 
> The "arcane ritual" should be really well documented by now, it's in
> Documentation/SubmittingPatches in your kernel tree, and you can read it
> online at:
> 	https://www.kernel.org/doc/html/latest/process/submitting-patches.html
> 
> 
>> i rediffed against HEAD even though the two weeks old patch still applied
>> cleanly with +2 offset.
>>
>> # stepping off soap box # actual technical content starts here #
>>
>> this is a followup to that thread from 2018-11:
>> https://www.spinics.net/lists/arm-kernel/msg685598.html
>>
>> the issue was discussed in more detail than i can claim
>> to fully understand back then, but no fix ever merged.
>> but i would really like to use rtl_433 on a raspi without
>> having to build a custom-patched kernel first.
>>
>> the attached patch is my stripdown/cleanup of a devel-diff
>> provided to me by the original reporter Steve Markgraf.
>> credits to him for the good parts, blame to me for the bad parts.
>>
>> this does not cover the additional case of "PIO-based usb controllers"
>> mainly because i dont understand what that means (or how to handle it)
>> and if its broken right now (as the thread indicates) it might
>> as well stay broken until someone who understands cares enough.
>>
>> could you please get this on track for merging?
> 
> 
>>
>> regards,
>>    x23
>>
>>
>>
> 
>> diff --git a/drivers/usb/core/devio.c b/drivers/usb/core/devio.c
>> index b265ab5405f9..69594c2169ea 100644
>> --- a/drivers/usb/core/devio.c
>> +++ b/drivers/usb/core/devio.c
>> @@ -238,9 +238,14 @@ static int usbdev_mmap(struct file *file, struct vm_area_struct *vma)
>>   	usbm->vma_use_count = 1;
>>   	INIT_LIST_HEAD(&usbm->memlist);
>>   
>> +#ifdef CONFIG_X86
>>   	if (remap_pfn_range(vma, vma->vm_start,
>>   			virt_to_phys(usbm->mem) >> PAGE_SHIFT,
>>   			size, vma->vm_page_prot) < 0) {
>> +#else /* !CONFIG_X86 */
>> +	if (dma_mmap_coherent(ps->dev->bus->sysdev,
>> +			vma, mem, dma_handle, size) < 0) {
>> +#endif /* !CONFIG_X86 */
>>   		dec_usb_memory_use_count(usbm, &usbm->vma_use_count);
>>   		return -EAGAIN;
>>   	}
> 
> First off, we need this in a format we could apply it in (hint, read the
> above links).
> 
> But the main issue here is what exactly is this "fixing"?  What is wrong
> with the existing code that non-x86 systems have such a problem with?
> Shouldn't all of these dma issues be handled by the platform with the
> remap_pfn_range() call itself?

If usbm->mem is (or ever can be) a CPU address returned by 
dma_alloc_coherent(), then doing virt_to_phys() on it is bogus and may 
yield a nonsense 'PFN' to begin with. However, it it can can ever come 
from a regular page allocation/kmalloc/vmalloc then unconditionally 
passing it to dma_mmap_coherent wouldn't be right either.

Robin.

> 
> What is the problem that you are having?
> 
> thanks,
> 
> greg k-h
> 
> _______________________________________________
> linux-arm-kernel mailing list
> linux-arm-kernel@lists.infradead.org
> http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
>
Russell King - ARM Linux admin Aug. 8, 2019, 9:59 a.m. UTC | #3
On Thu, Aug 08, 2019 at 10:58:11AM +0200, Greg KH wrote:
> But the main issue here is what exactly is this "fixing"?  What is wrong
> with the existing code that non-x86 systems have such a problem with?
> Shouldn't all of these dma issues be handled by the platform with the
> remap_pfn_range() call itself?

remap_pfn_range() takes a PFN.  virt_to_phys() converts a kernel *direct
mapped* virtual address to a physical address.  That much is fine.

The question is - what is usbm->mem?  If that is anything other than an
address returned by kmalloc() or from the normal page allocator, then
virt_to_phys() will return garbage.

In other words, if it comes from dma_alloc_coherent(), vmalloc() or
ioremap(), using virt_to_phys() on it results in garbage.

This aspect of virt_to_phys() has been well known about for ages; it's
one of the fundamentals of kernel programming.
Oliver Neukum Aug. 8, 2019, 10:02 a.m. UTC | #4
Am Donnerstag, den 08.08.2019, 10:59 +0100 schrieb Russell King - ARM
Linux admin:
> On Thu, Aug 08, 2019 at 10:58:11AM +0200, Greg KH wrote:
> > But the main issue here is what exactly is this "fixing"?  What is wrong
> > with the existing code that non-x86 systems have such a problem with?
> > Shouldn't all of these dma issues be handled by the platform with the
> > remap_pfn_range() call itself?
> 
> remap_pfn_range() takes a PFN.  virt_to_phys() converts a kernel *direct
> mapped* virtual address to a physical address.  That much is fine.
> 
> The question is - what is usbm->mem?  If that is anything other than an
> address returned by kmalloc() or from the normal page allocator, then
> virt_to_phys() will return garbage.
> 
> In other words, if it comes from dma_alloc_coherent(), vmalloc() or
> ioremap(), using virt_to_phys() on it results in garbage.

It comes from usb_alloc_coherent() -> hcd_buffer_alloc() ->
hcd_buffer_alloc()

That function is a bit complicated. so I rather quote than explain:

        if (hcd->localmem_pool)
                return gen_pool_dma_alloc(hcd->localmem_pool, size, dma)

        /* some USB hosts just use PIO */
        if (!IS_ENABLED(CONFIG_HAS_DMA) ||
            !is_device_dma_capable(bus->sysdev)) {
                *dma = ~(dma_addr_t) 0;
                return kmalloc(size, mem_flags);
        }

        for (i = 0; i < HCD_BUFFER_POOLS; i++) {
                if (size <= pool_max[i])
                        return dma_pool_alloc(hcd->pool[i], mem_flags, dma);
        }

        return dma_alloc_coherent(hcd->self.sysdev, size, dma, mem_flags);

	Regards
		Oliver
Greg KH Aug. 8, 2019, 10:07 a.m. UTC | #5
On Thu, Aug 08, 2019 at 10:46:24AM +0100, Robin Murphy wrote:
> On 2019-08-08 9:58 am, Greg KH wrote:
> > On Thu, Aug 08, 2019 at 10:46:36AM +0200, yvahkhfo.1df7f8c2@hashmail.org wrote:
> > > Hello linux-usb and linux-arm.
> > > 
> > > Ccing security@ because "the kernel dma code is mapping randomish
> > > kernel/user mem to a user process" seems to have security implications
> > > even though i didnt research that aspect past "its a 100% reliable way
> > > to crash a raspi from userspace".
> > > 
> > > tried submitting this through linux-arm-kernel ~2 weeks ago but
> > > the only "response" i got was phishing-spam.
> > > tried to follow up through raspi-internals chat, they suggested
> > > i try linux-usb instead, but otoh the original reporter was
> > > deflected from -usb to "try some other mls, they might care".
> > > https://www.spinics.net/lists/linux-usb/msg173277.html
> > > 
> > > if i am not following some arcane ritual or indenting convention required
> > > by regular users of these lists i apologize in advance, but i am not a
> > > kernel developer, i am just here as a user with a bug and a patch.
> > > (and the vger FAQ link 404s...)
> > 
> > The "arcane ritual" should be really well documented by now, it's in
> > Documentation/SubmittingPatches in your kernel tree, and you can read it
> > online at:
> > 	https://www.kernel.org/doc/html/latest/process/submitting-patches.html
> > 
> > 
> > > i rediffed against HEAD even though the two weeks old patch still applied
> > > cleanly with +2 offset.
> > > 
> > > # stepping off soap box # actual technical content starts here #
> > > 
> > > this is a followup to that thread from 2018-11:
> > > https://www.spinics.net/lists/arm-kernel/msg685598.html
> > > 
> > > the issue was discussed in more detail than i can claim
> > > to fully understand back then, but no fix ever merged.
> > > but i would really like to use rtl_433 on a raspi without
> > > having to build a custom-patched kernel first.
> > > 
> > > the attached patch is my stripdown/cleanup of a devel-diff
> > > provided to me by the original reporter Steve Markgraf.
> > > credits to him for the good parts, blame to me for the bad parts.
> > > 
> > > this does not cover the additional case of "PIO-based usb controllers"
> > > mainly because i dont understand what that means (or how to handle it)
> > > and if its broken right now (as the thread indicates) it might
> > > as well stay broken until someone who understands cares enough.
> > > 
> > > could you please get this on track for merging?
> > 
> > 
> > > 
> > > regards,
> > >    x23
> > > 
> > > 
> > > 
> > 
> > > diff --git a/drivers/usb/core/devio.c b/drivers/usb/core/devio.c
> > > index b265ab5405f9..69594c2169ea 100644
> > > --- a/drivers/usb/core/devio.c
> > > +++ b/drivers/usb/core/devio.c
> > > @@ -238,9 +238,14 @@ static int usbdev_mmap(struct file *file, struct vm_area_struct *vma)
> > >   	usbm->vma_use_count = 1;
> > >   	INIT_LIST_HEAD(&usbm->memlist);
> > > +#ifdef CONFIG_X86
> > >   	if (remap_pfn_range(vma, vma->vm_start,
> > >   			virt_to_phys(usbm->mem) >> PAGE_SHIFT,
> > >   			size, vma->vm_page_prot) < 0) {
> > > +#else /* !CONFIG_X86 */
> > > +	if (dma_mmap_coherent(ps->dev->bus->sysdev,
> > > +			vma, mem, dma_handle, size) < 0) {
> > > +#endif /* !CONFIG_X86 */
> > >   		dec_usb_memory_use_count(usbm, &usbm->vma_use_count);
> > >   		return -EAGAIN;
> > >   	}
> > 
> > First off, we need this in a format we could apply it in (hint, read the
> > above links).
> > 
> > But the main issue here is what exactly is this "fixing"?  What is wrong
> > with the existing code that non-x86 systems have such a problem with?
> > Shouldn't all of these dma issues be handled by the platform with the
> > remap_pfn_range() call itself?
> 
> If usbm->mem is (or ever can be) a CPU address returned by
> dma_alloc_coherent(), then doing virt_to_phys() on it is bogus and may yield
> a nonsense 'PFN' to begin with. However, it it can can ever come from a
> regular page allocation/kmalloc/vmalloc then unconditionally passing it to
> dma_mmap_coherent wouldn't be right either.

usbm->mem comes from a call to usb_alloc_coherent() which calls
hcd_buffer_alloc() which tries to allocate memory in the best possible
way for that specific host controller.  If the host controller has a
pool of memory, it uses that, if the host controller has PIO it uses
kmalloc(), if there are some "pools" of host controller memory it uses
dma_pool_alloc() and as a total last resort, calls dma_alloc_coherent().

So yes, this could happen.

So how to fix this properly?  What host controller driver is being used
here that ends up defaulting to dma_alloc_coherent()?  Shouldn't that be
fixed up no matter what?

And then, if what you say is correct then a real fix for devio.c could
be made, but that is NOT going to just depend on the arch the system is
running on, as all of this depends on the host controller being accessed
at that moment for that device.

thanks,

greg k-h
Robin Murphy Aug. 8, 2019, 10:43 a.m. UTC | #6
On 2019-08-08 11:07 am, Greg KH wrote:
> On Thu, Aug 08, 2019 at 10:46:24AM +0100, Robin Murphy wrote:
>> On 2019-08-08 9:58 am, Greg KH wrote:
>>> On Thu, Aug 08, 2019 at 10:46:36AM +0200, yvahkhfo.1df7f8c2@hashmail.org wrote:
>>>> Hello linux-usb and linux-arm.
>>>>
>>>> Ccing security@ because "the kernel dma code is mapping randomish
>>>> kernel/user mem to a user process" seems to have security implications
>>>> even though i didnt research that aspect past "its a 100% reliable way
>>>> to crash a raspi from userspace".
>>>>
>>>> tried submitting this through linux-arm-kernel ~2 weeks ago but
>>>> the only "response" i got was phishing-spam.
>>>> tried to follow up through raspi-internals chat, they suggested
>>>> i try linux-usb instead, but otoh the original reporter was
>>>> deflected from -usb to "try some other mls, they might care".
>>>> https://www.spinics.net/lists/linux-usb/msg173277.html
>>>>
>>>> if i am not following some arcane ritual or indenting convention required
>>>> by regular users of these lists i apologize in advance, but i am not a
>>>> kernel developer, i am just here as a user with a bug and a patch.
>>>> (and the vger FAQ link 404s...)
>>>
>>> The "arcane ritual" should be really well documented by now, it's in
>>> Documentation/SubmittingPatches in your kernel tree, and you can read it
>>> online at:
>>> 	https://www.kernel.org/doc/html/latest/process/submitting-patches.html
>>>
>>>
>>>> i rediffed against HEAD even though the two weeks old patch still applied
>>>> cleanly with +2 offset.
>>>>
>>>> # stepping off soap box # actual technical content starts here #
>>>>
>>>> this is a followup to that thread from 2018-11:
>>>> https://www.spinics.net/lists/arm-kernel/msg685598.html
>>>>
>>>> the issue was discussed in more detail than i can claim
>>>> to fully understand back then, but no fix ever merged.
>>>> but i would really like to use rtl_433 on a raspi without
>>>> having to build a custom-patched kernel first.
>>>>
>>>> the attached patch is my stripdown/cleanup of a devel-diff
>>>> provided to me by the original reporter Steve Markgraf.
>>>> credits to him for the good parts, blame to me for the bad parts.
>>>>
>>>> this does not cover the additional case of "PIO-based usb controllers"
>>>> mainly because i dont understand what that means (or how to handle it)
>>>> and if its broken right now (as the thread indicates) it might
>>>> as well stay broken until someone who understands cares enough.
>>>>
>>>> could you please get this on track for merging?
>>>
>>>
>>>>
>>>> regards,
>>>>     x23
>>>>
>>>>
>>>>
>>>
>>>> diff --git a/drivers/usb/core/devio.c b/drivers/usb/core/devio.c
>>>> index b265ab5405f9..69594c2169ea 100644
>>>> --- a/drivers/usb/core/devio.c
>>>> +++ b/drivers/usb/core/devio.c
>>>> @@ -238,9 +238,14 @@ static int usbdev_mmap(struct file *file, struct vm_area_struct *vma)
>>>>    	usbm->vma_use_count = 1;
>>>>    	INIT_LIST_HEAD(&usbm->memlist);
>>>> +#ifdef CONFIG_X86
>>>>    	if (remap_pfn_range(vma, vma->vm_start,
>>>>    			virt_to_phys(usbm->mem) >> PAGE_SHIFT,
>>>>    			size, vma->vm_page_prot) < 0) {
>>>> +#else /* !CONFIG_X86 */
>>>> +	if (dma_mmap_coherent(ps->dev->bus->sysdev,
>>>> +			vma, mem, dma_handle, size) < 0) {
>>>> +#endif /* !CONFIG_X86 */
>>>>    		dec_usb_memory_use_count(usbm, &usbm->vma_use_count);
>>>>    		return -EAGAIN;
>>>>    	}
>>>
>>> First off, we need this in a format we could apply it in (hint, read the
>>> above links).
>>>
>>> But the main issue here is what exactly is this "fixing"?  What is wrong
>>> with the existing code that non-x86 systems have such a problem with?
>>> Shouldn't all of these dma issues be handled by the platform with the
>>> remap_pfn_range() call itself?
>>
>> If usbm->mem is (or ever can be) a CPU address returned by
>> dma_alloc_coherent(), then doing virt_to_phys() on it is bogus and may yield
>> a nonsense 'PFN' to begin with. However, it it can can ever come from a
>> regular page allocation/kmalloc/vmalloc then unconditionally passing it to
>> dma_mmap_coherent wouldn't be right either.
> 
> usbm->mem comes from a call to usb_alloc_coherent() which calls
> hcd_buffer_alloc() which tries to allocate memory in the best possible
> way for that specific host controller.  If the host controller has a
> pool of memory, it uses that, if the host controller has PIO it uses
> kmalloc(), if there are some "pools" of host controller memory it uses
> dma_pool_alloc() and as a total last resort, calls dma_alloc_coherent().
> 
> So yes, this could happen.
> 
> So how to fix this properly?  What host controller driver is being used
> here that ends up defaulting to dma_alloc_coherent()?  Shouldn't that be
> fixed up no matter what?
> 
> And then, if what you say is correct then a real fix for devio.c could
> be made, but that is NOT going to just depend on the arch the system is
> running on, as all of this depends on the host controller being accessed
> at that moment for that device.

Right, in that case we'd probably want some kind of usb_mmap_coherent() 
helper to encapsulate equivalent logic to usb_{alloc,free}_coherent() to 
figure out which remap operation is appropriate. It's absolutely not an 
arch-specific thing.

Robin.
Greg KH Aug. 8, 2019, 1:05 p.m. UTC | #7
On Thu, Aug 08, 2019 at 12:07:26PM +0200, Greg KH wrote:
> On Thu, Aug 08, 2019 at 10:46:24AM +0100, Robin Murphy wrote:
> > On 2019-08-08 9:58 am, Greg KH wrote:
> > > On Thu, Aug 08, 2019 at 10:46:36AM +0200, yvahkhfo.1df7f8c2@hashmail.org wrote:
> > > > Hello linux-usb and linux-arm.
> > > > 
> > > > Ccing security@ because "the kernel dma code is mapping randomish
> > > > kernel/user mem to a user process" seems to have security implications
> > > > even though i didnt research that aspect past "its a 100% reliable way
> > > > to crash a raspi from userspace".
> > > > 
> > > > tried submitting this through linux-arm-kernel ~2 weeks ago but
> > > > the only "response" i got was phishing-spam.
> > > > tried to follow up through raspi-internals chat, they suggested
> > > > i try linux-usb instead, but otoh the original reporter was
> > > > deflected from -usb to "try some other mls, they might care".
> > > > https://www.spinics.net/lists/linux-usb/msg173277.html
> > > > 
> > > > if i am not following some arcane ritual or indenting convention required
> > > > by regular users of these lists i apologize in advance, but i am not a
> > > > kernel developer, i am just here as a user with a bug and a patch.
> > > > (and the vger FAQ link 404s...)
> > > 
> > > The "arcane ritual" should be really well documented by now, it's in
> > > Documentation/SubmittingPatches in your kernel tree, and you can read it
> > > online at:
> > > 	https://www.kernel.org/doc/html/latest/process/submitting-patches.html
> > > 
> > > 
> > > > i rediffed against HEAD even though the two weeks old patch still applied
> > > > cleanly with +2 offset.
> > > > 
> > > > # stepping off soap box # actual technical content starts here #
> > > > 
> > > > this is a followup to that thread from 2018-11:
> > > > https://www.spinics.net/lists/arm-kernel/msg685598.html
> > > > 
> > > > the issue was discussed in more detail than i can claim
> > > > to fully understand back then, but no fix ever merged.
> > > > but i would really like to use rtl_433 on a raspi without
> > > > having to build a custom-patched kernel first.
> > > > 
> > > > the attached patch is my stripdown/cleanup of a devel-diff
> > > > provided to me by the original reporter Steve Markgraf.
> > > > credits to him for the good parts, blame to me for the bad parts.
> > > > 
> > > > this does not cover the additional case of "PIO-based usb controllers"
> > > > mainly because i dont understand what that means (or how to handle it)
> > > > and if its broken right now (as the thread indicates) it might
> > > > as well stay broken until someone who understands cares enough.
> > > > 
> > > > could you please get this on track for merging?
> > > 
> > > 
> > > > 
> > > > regards,
> > > >    x23
> > > > 
> > > > 
> > > > 
> > > 
> > > > diff --git a/drivers/usb/core/devio.c b/drivers/usb/core/devio.c
> > > > index b265ab5405f9..69594c2169ea 100644
> > > > --- a/drivers/usb/core/devio.c
> > > > +++ b/drivers/usb/core/devio.c
> > > > @@ -238,9 +238,14 @@ static int usbdev_mmap(struct file *file, struct vm_area_struct *vma)
> > > >   	usbm->vma_use_count = 1;
> > > >   	INIT_LIST_HEAD(&usbm->memlist);
> > > > +#ifdef CONFIG_X86
> > > >   	if (remap_pfn_range(vma, vma->vm_start,
> > > >   			virt_to_phys(usbm->mem) >> PAGE_SHIFT,
> > > >   			size, vma->vm_page_prot) < 0) {
> > > > +#else /* !CONFIG_X86 */
> > > > +	if (dma_mmap_coherent(ps->dev->bus->sysdev,
> > > > +			vma, mem, dma_handle, size) < 0) {
> > > > +#endif /* !CONFIG_X86 */
> > > >   		dec_usb_memory_use_count(usbm, &usbm->vma_use_count);
> > > >   		return -EAGAIN;
> > > >   	}
> > > 
> > > First off, we need this in a format we could apply it in (hint, read the
> > > above links).
> > > 
> > > But the main issue here is what exactly is this "fixing"?  What is wrong
> > > with the existing code that non-x86 systems have such a problem with?
> > > Shouldn't all of these dma issues be handled by the platform with the
> > > remap_pfn_range() call itself?
> > 
> > If usbm->mem is (or ever can be) a CPU address returned by
> > dma_alloc_coherent(), then doing virt_to_phys() on it is bogus and may yield
> > a nonsense 'PFN' to begin with. However, it it can can ever come from a
> > regular page allocation/kmalloc/vmalloc then unconditionally passing it to
> > dma_mmap_coherent wouldn't be right either.
> 
> usbm->mem comes from a call to usb_alloc_coherent() which calls
> hcd_buffer_alloc() which tries to allocate memory in the best possible
> way for that specific host controller.  If the host controller has a
> pool of memory, it uses that, if the host controller has PIO it uses
> kmalloc(), if there are some "pools" of host controller memory it uses
> dma_pool_alloc() and as a total last resort, calls dma_alloc_coherent().
> 
> So yes, this could happen.
> 
> So how to fix this properly?  What host controller driver is being used
> here that ends up defaulting to dma_alloc_coherent()?  Shouldn't that be
> fixed up no matter what?
> 
> And then, if what you say is correct then a real fix for devio.c could
> be made, but that is NOT going to just depend on the arch the system is
> running on, as all of this depends on the host controller being accessed
> at that moment for that device.

Also see this thread:
	https://lore.kernel.org/linux-usb/20190801220134.3295-1-gavinli@thegavinli.com/

where this just came up and how the proposed patch here would cause
warnings to occur in the kernel log of users for no good reason.  That
issue is supposed to be fixed "soon"...

thanks,

greg k-h
Christoph Hellwig Aug. 8, 2019, 4:10 p.m. UTC | #8
On Thu, Aug 08, 2019 at 10:46:36AM +0200, yvahkhfo.1df7f8c2@hashmail.org wrote:
> --- a/drivers/usb/core/devio.c
> +++ b/drivers/usb/core/devio.c
> @@ -238,9 +238,14 @@ static int usbdev_mmap(struct file *file, struct vm_area_struct *vma)
>  	usbm->vma_use_count = 1;
>  	INIT_LIST_HEAD(&usbm->memlist);
>  
> +#ifdef CONFIG_X86
>  	if (remap_pfn_range(vma, vma->vm_start,
>  			virt_to_phys(usbm->mem) >> PAGE_SHIFT,
>  			size, vma->vm_page_prot) < 0) {
> +#else /* !CONFIG_X86 */
> +	if (dma_mmap_coherent(ps->dev->bus->sysdev, 
> +			vma, mem, dma_handle, size) < 0) {
> +#endif /* !CONFIG_X86 */

Doing the dma_mmap_coherent unconditionally is the right thing here.
Gavin who is on Cc has been looking into that.

Note that you'll also need this patch which I'm going to send to Linus
this week before it properly works on x86:

http://git.infradead.org/users/hch/dma-mapping.git/commitdiff/197b3e665b82c6027be5c68a143233df7ce5224f
Christoph Hellwig Aug. 8, 2019, 4:12 p.m. UTC | #9
On Thu, Aug 08, 2019 at 09:10:15AM -0700, Christoph Hellwig wrote:
> On Thu, Aug 08, 2019 at 10:46:36AM +0200, yvahkhfo.1df7f8c2@hashmail.org wrote:
> > --- a/drivers/usb/core/devio.c
> > +++ b/drivers/usb/core/devio.c
> > @@ -238,9 +238,14 @@ static int usbdev_mmap(struct file *file, struct vm_area_struct *vma)
> >  	usbm->vma_use_count = 1;
> >  	INIT_LIST_HEAD(&usbm->memlist);
> >  
> > +#ifdef CONFIG_X86
> >  	if (remap_pfn_range(vma, vma->vm_start,
> >  			virt_to_phys(usbm->mem) >> PAGE_SHIFT,
> >  			size, vma->vm_page_prot) < 0) {
> > +#else /* !CONFIG_X86 */
> > +	if (dma_mmap_coherent(ps->dev->bus->sysdev, 
> > +			vma, mem, dma_handle, size) < 0) {
> > +#endif /* !CONFIG_X86 */
> 
> Doing the dma_mmap_coherent unconditionally is the right thing here.
> Gavin who is on Cc has been looking into that.

Ok, tht is assuming it always is dma_alloc_* memory which apparently
it isn't.  But the arch ifdef for sure is wrong.
Russell King - ARM Linux admin Aug. 8, 2019, 4:57 p.m. UTC | #10
On Thu, Aug 08, 2019 at 09:10:15AM -0700, Christoph Hellwig wrote:
> On Thu, Aug 08, 2019 at 10:46:36AM +0200, yvahkhfo.1df7f8c2@hashmail.org wrote:
> > --- a/drivers/usb/core/devio.c
> > +++ b/drivers/usb/core/devio.c
> > @@ -238,9 +238,14 @@ static int usbdev_mmap(struct file *file, struct vm_area_struct *vma)
> >  	usbm->vma_use_count = 1;
> >  	INIT_LIST_HEAD(&usbm->memlist);
> >  
> > +#ifdef CONFIG_X86
> >  	if (remap_pfn_range(vma, vma->vm_start,
> >  			virt_to_phys(usbm->mem) >> PAGE_SHIFT,
> >  			size, vma->vm_page_prot) < 0) {
> > +#else /* !CONFIG_X86 */
> > +	if (dma_mmap_coherent(ps->dev->bus->sysdev, 
> > +			vma, mem, dma_handle, size) < 0) {
> > +#endif /* !CONFIG_X86 */
> 
> Doing the dma_mmap_coherent unconditionally is the right thing here.

So what if usbm->mem is from kmalloc because the host doesn't support DMA?

Patch
diff mbox series

diff --git a/drivers/usb/core/devio.c b/drivers/usb/core/devio.c
index b265ab5405f9..69594c2169ea 100644
--- a/drivers/usb/core/devio.c
+++ b/drivers/usb/core/devio.c
@@ -238,9 +238,14 @@  static int usbdev_mmap(struct file *file, struct vm_area_struct *vma)
 	usbm->vma_use_count = 1;
 	INIT_LIST_HEAD(&usbm->memlist);
 
+#ifdef CONFIG_X86
 	if (remap_pfn_range(vma, vma->vm_start,
 			virt_to_phys(usbm->mem) >> PAGE_SHIFT,
 			size, vma->vm_page_prot) < 0) {
+#else /* !CONFIG_X86 */
+	if (dma_mmap_coherent(ps->dev->bus->sysdev, 
+			vma, mem, dma_handle, size) < 0) {
+#endif /* !CONFIG_X86 */
 		dec_usb_memory_use_count(usbm, &usbm->vma_use_count);
 		return -EAGAIN;
 	}