From: damian.tometzki@icloud.com (Damian Tometzki)
To: kernelnewbies@lists.kernelnewbies.org
Subject: Virtual Memory map
Date: Wed, 13 Dec 2017 09:28:33 +0100 [thread overview]
Message-ID: <AC5A5D5F-76FF-481B-A180-A16709AFA368@icloud.com> (raw)
In-Reply-To: <CAKsu7qzTgM8SVJY9Yy6faKp4+x0N2--POzJ-R-=1u9hZj4eHkQ@mail.gmail.com>
Hello,
On more question. The second example:
>> ffff800000000000 - ffff87ffffffffff (=43 bits) guard hole, reserved for hypervisor
What are the relation between the Bits (=43bits) and the Adresse Range ?
Is it possible to calculate the 43 Bits from the range ? If yes, how ?
Best regards
Damian
> Am 13.12.2017 um 05:35 schrieb arshad hussain <arshad.super@gmail.com>:
>
> On Wed, Dec 13, 2017 at 12:44 AM, Damian Tometzki
> <damian.tometzki@icloud.com> wrote:
>> Hello all,
>>
>> i have a short question:
>>
>> How are the bits (in brackets) calculated in the virtual memory map ?
>>
>> for example the first line (=47 bits)
>>
>> Virtual memory map with 4 level page tables:
>>
>> 0000000000000000 - 00007fffffffffff (=47 bits) user space, different per mm
>> hole caused by [47:63] sign extension
>> ffff800000000000 - ffff87ffffffffff (=43 bits) guard hole, reserved for hypervisor
>>
>
> Presently for x86-64 kernel uses 4-level paging. Out of 64bit only 48 bit
> is enabled (Which boils down to Terabyte of address space). For case
> where getpagesize() is 4K the breakup is :-
>
> CR3 -> Global(9 bits) -> Upper(9 bits) -> Middle(9 bits) -> Page
> table(9 bits) -> [12 bits for page or 4096 bytes] = (48 bits)
>
> Thanks
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next prev parent reply other threads:[~2017-12-13 8:28 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-12-12 19:14 Virtual Memory map Damian Tometzki
2017-12-13 2:59 ` valdis.kletnieks at vt.edu
2017-12-13 4:35 ` arshad hussain
2017-12-13 8:28 ` Damian Tometzki [this message]
2017-12-13 10:44 ` arshad hussain
2017-12-12 20:18 Virtual Memory Map Damian Tometzki
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