Date: Thu, 27 Oct 2011 07:55:19 -0500 From: Mark Tinguely <marktinguely@gmail.com> To: Daniel Grech <dgre090@gmail.com> Cc: freebsd-hackers@freebsd.org Subject: Re: Kernel Space Memory Allocation Message-ID: <4EA954B7.7070205@gmail.com> In-Reply-To: <CAG167sYaz3=Qvv0YYP7YvSkgm2HKkdP-XDu=HBUMv8TV1QUd5A@mail.gmail.com> References: <CAG167sYaz3=Qvv0YYP7YvSkgm2HKkdP-XDu=HBUMv8TV1QUd5A@mail.gmail.com>
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On 10/27/2011 3:31 AM, Daniel Grech wrote:
> Hi,
>
> I am allocating memory from a device driver in the kernel and passing it on
> to another driver. In the other driver it is neccessary for me to determine
> whether the address passed is from user space or kernel space as this driver
> can also be called from user space. I am currently using the following check
> to determine if the address is in kernel space or userspace :
>
> if ( ( (char *) VM_MIN_KERNEL_ADDRESS<= address)&& (address<= (char *)
> VM_MAX_KERNEL_ADDRESS) )
> {
> KERNEL SPACE
> }
> else
> {
> USER SPACE
> }
>
> However, this does not always work. Sometimes although I allocate memory in
> the kernel using the malloc macro, this returns an address which is not in
> the above range. Is there any workaround for this problem?
>
> Thanks in advance for your help.
>
> Daniel
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>
Be careful if using user virtual addresses in DMA POST commands, because
the interrupt handler may not have the the same address space as the
caller. For example: BUS_DMASYNC_POSTREAD copying a bounce buffer to a
user VA.
--Mark Tinguely
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