physical memory userspace/kernel split on Linux x86-64

physical memory userspace/kernel split on Linux x86-64

[Le Tan]

Hi,
Is there an explict split between userspace and kernel in physical
memory on Linux x86-64? That is, given a physical address, can I tell
whether this address is from userspace or not?
As far as I know, in virtual address space, the kernel will use the
upper half and the userspace will use the lower half. But what about
in physical address space?

Thanks very much!

Le

physical memory userspace/kernel split on Linux x86-64

[Karaoui mohamed lamine]

2015-05-27 3:12 GMT+02:00 Le Tan <tamlokveer@gmail.com>:

> Hi,
> Is there an explict split between userspace and kernel in physical
> memory on Linux x86-64? That is, given a physical address, can I tell
> whether this address is from userspace or not?
>

No. The same physical address can be  used by both the kernel and the
userspace.
The kernel and userspace share the same physical memory.
Any memory page can be allocated for the userspace then released (free)
then re-allocated for kernel use.

As far as I know, in virtual address space, the kernel will use the
> upper half and the userspace will use the lower half. But what about
> in physical address space?


> Thanks very much!
>
> Le
>
> _______________________________________________
> Kernelnewbies mailing list
> Kernelnewbies at kernelnewbies.org
> http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
>
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physical memory userspace/kernel split on Linux x86-64

[Le Tan]

Hi,

2015-05-27 21:54 GMT+08:00 Karaoui mohamed lamine <moharaka@gmail.com>:
> 2015-05-27 3:12 GMT+02:00 Le Tan <tamlokveer@gmail.com>:
>>
>> Hi,
>> Is there an explict split between userspace and kernel in physical
>> memory on Linux x86-64? That is, given a physical address, can I tell
>> whether this address is from userspace or not?
>
>
> No. The same physical address can be  used by both the kernel and the
> userspace.
> The kernel and userspace share the same physical memory.
> Any memory page can be allocated for the userspace then released (free) then
> re-allocated for kernel use.

Got it. Thanks very much!

>> As far as I know, in virtual address space, the kernel will use the
>> upper half and the userspace will use the lower half. But what about
>> in physical address space?
>>
>>
>> Thanks very much!
>>
>> Le
>>
>> _______________________________________________
>> Kernelnewbies mailing list
>> Kernelnewbies at kernelnewbies.org
>> http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
>
>

physical memory userspace/kernel split on Linux x86-64

[Min-Hua Chen]

Hi,

Linux kernel basically manages all available physical memory pages.
If user-space need a page, kernel allocates a page for it. Hence a
physical page may be in mapped to user-space virtual address or 
kernel-space virtual address or both.

The user-space and kernel-space exist in virtual address space, not
physical.

Thanks,
Min-Hua

On Wed, May 27, 2015 at 09:12:11AM +0800, Le Tan wrote:
> Hi,
> Is there an explict split between userspace and kernel in physical
> memory on Linux x86-64? That is, given a physical address, can I tell
> whether this address is from userspace or not?
> As far as I know, in virtual address space, the kernel will use the
> upper half and the userspace will use the lower half. But what about
> in physical address space?
> 
> Thanks very much!
> 
> Le
> 
> _______________________________________________
> Kernelnewbies mailing list
> Kernelnewbies at kernelnewbies.org
> http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies

physical memory userspace/kernel split on Linux x86-64

[Le Tan]

Hi Min-Hua,

2015-05-27 22:23 GMT+08:00 Min-Hua Chen <orca.chen@gmail.com>:
> Hi,
>
> Linux kernel basically manages all available physical memory pages.
> If user-space need a page, kernel allocates a page for it. Hence a
> physical page may be in mapped to user-space virtual address or
> kernel-space virtual address or both.
>
> The user-space and kernel-space exist in virtual address space, not
> physical.

Very clear description! I always seems to be confused by some basic concept. :)

Thanks!

Le

> Thanks,
> Min-Hua
>
> On Wed, May 27, 2015 at 09:12:11AM +0800, Le Tan wrote:
>> Hi,
>> Is there an explict split between userspace and kernel in physical
>> memory on Linux x86-64? That is, given a physical address, can I tell
>> whether this address is from userspace or not?
>> As far as I know, in virtual address space, the kernel will use the
>> upper half and the userspace will use the lower half. But what about
>> in physical address space?
>>
>> Thanks very much!
>>
>> Le
>>
>> _______________________________________________
>> Kernelnewbies mailing list
>> Kernelnewbies at kernelnewbies.org
>> http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies