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How a 64-bit process virtual address space is divided in Linux?



The Next CEO of Stack OverflowLinux Kernel logical address space organisationhow is page size determined in virtual address space?Physical Address Extension - how do virtual addresses work?How can two identical virtual addresses point to different physical addresses?How does the CPU knows which physical address is mapped to which virtual address?how to get virtual address generated by a processHow can the Linux kernel address from 8 MB to 1 GB of virtual memory in x86 systemsDoes the isolation between virtual memory address spaces of different processes not apply to privileged process and to swap?Do the virtual address spaces of all the processes have the same content in their “Kernel” parts?Disabling virtual address space randomization for a linux kernel module










6















The following image shows how a 32-bit process virtual address space is divided:



enter image description here



But how a 64-bit process virtual address space is divided?










share|improve this question


























    6















    The following image shows how a 32-bit process virtual address space is divided:



    enter image description here



    But how a 64-bit process virtual address space is divided?










    share|improve this question
























      6












      6








      6


      1






      The following image shows how a 32-bit process virtual address space is divided:



      enter image description here



      But how a 64-bit process virtual address space is divided?










      share|improve this question














      The following image shows how a 32-bit process virtual address space is divided:



      enter image description here



      But how a 64-bit process virtual address space is divided?







      linux






      share|improve this question













      share|improve this question











      share|improve this question




      share|improve this question










      asked 11 hours ago









      ChristopherChristopher

      1532




      1532




















          1 Answer
          1






          active

          oldest

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          5














          The 64-bit x86 virtual memory map splits the address space into two: the lower section (with the top bit set to 0) is user-space, the upper section (with the top bit set to 1) is kernel-space. (Note that x86-64 defines “canonical” “lower half” and “higher half” addresses, with a number of bits effectively limited to 48 or 56; see Wikipedia for details.)



          The complete map is documented in detail in the kernel; currently it looks like



          ===========================================================================================
          Start addr | Offset | End addr | Size | VM area description
          ===========================================================================================
          | | | |
          0000000000000000 | 0 | 00007fffffffffff | 128 TB | user-space virtual memory
          __________________|____________|__________________|_________|______________________________
          | | | |
          0000800000000000 | +128 TB | ffff7fffffffffff | ~16M TB | non-canonical
          __________________|____________|__________________|_________|______________________________
          | | | |
          ffff800000000000 | -128 TB | ffffffffffffffff | 128 TB | kernel-space virtual memory
          __________________|____________|__________________|_________|______________________________


          with 48-bit virtual addresses.



          Unlike the 32-bit case, the “64-bit” memory map is a direct reflection of hardware constraints.






          share|improve this answer

























          • To clarify: this limitation is imposed by the hardware. There is currently no 64-bit processor implementation that doesn't leave a huge hole of unusable addresses in the middle of the virtual address space. The amount of physical memory the CPUs are able to address is also way below 2 to the power of 64.

            – Johan Myréen
            9 hours ago











          • Thanks @Johan, I’ve tried to highlight this.

            – Stephen Kitt
            9 hours ago











          Your Answer








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          1 Answer
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          oldest

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          1 Answer
          1






          active

          oldest

          votes









          active

          oldest

          votes






          active

          oldest

          votes









          5














          The 64-bit x86 virtual memory map splits the address space into two: the lower section (with the top bit set to 0) is user-space, the upper section (with the top bit set to 1) is kernel-space. (Note that x86-64 defines “canonical” “lower half” and “higher half” addresses, with a number of bits effectively limited to 48 or 56; see Wikipedia for details.)



          The complete map is documented in detail in the kernel; currently it looks like



          ===========================================================================================
          Start addr | Offset | End addr | Size | VM area description
          ===========================================================================================
          | | | |
          0000000000000000 | 0 | 00007fffffffffff | 128 TB | user-space virtual memory
          __________________|____________|__________________|_________|______________________________
          | | | |
          0000800000000000 | +128 TB | ffff7fffffffffff | ~16M TB | non-canonical
          __________________|____________|__________________|_________|______________________________
          | | | |
          ffff800000000000 | -128 TB | ffffffffffffffff | 128 TB | kernel-space virtual memory
          __________________|____________|__________________|_________|______________________________


          with 48-bit virtual addresses.



          Unlike the 32-bit case, the “64-bit” memory map is a direct reflection of hardware constraints.






          share|improve this answer

























          • To clarify: this limitation is imposed by the hardware. There is currently no 64-bit processor implementation that doesn't leave a huge hole of unusable addresses in the middle of the virtual address space. The amount of physical memory the CPUs are able to address is also way below 2 to the power of 64.

            – Johan Myréen
            9 hours ago











          • Thanks @Johan, I’ve tried to highlight this.

            – Stephen Kitt
            9 hours ago















          5














          The 64-bit x86 virtual memory map splits the address space into two: the lower section (with the top bit set to 0) is user-space, the upper section (with the top bit set to 1) is kernel-space. (Note that x86-64 defines “canonical” “lower half” and “higher half” addresses, with a number of bits effectively limited to 48 or 56; see Wikipedia for details.)



          The complete map is documented in detail in the kernel; currently it looks like



          ===========================================================================================
          Start addr | Offset | End addr | Size | VM area description
          ===========================================================================================
          | | | |
          0000000000000000 | 0 | 00007fffffffffff | 128 TB | user-space virtual memory
          __________________|____________|__________________|_________|______________________________
          | | | |
          0000800000000000 | +128 TB | ffff7fffffffffff | ~16M TB | non-canonical
          __________________|____________|__________________|_________|______________________________
          | | | |
          ffff800000000000 | -128 TB | ffffffffffffffff | 128 TB | kernel-space virtual memory
          __________________|____________|__________________|_________|______________________________


          with 48-bit virtual addresses.



          Unlike the 32-bit case, the “64-bit” memory map is a direct reflection of hardware constraints.






          share|improve this answer

























          • To clarify: this limitation is imposed by the hardware. There is currently no 64-bit processor implementation that doesn't leave a huge hole of unusable addresses in the middle of the virtual address space. The amount of physical memory the CPUs are able to address is also way below 2 to the power of 64.

            – Johan Myréen
            9 hours ago











          • Thanks @Johan, I’ve tried to highlight this.

            – Stephen Kitt
            9 hours ago













          5












          5








          5







          The 64-bit x86 virtual memory map splits the address space into two: the lower section (with the top bit set to 0) is user-space, the upper section (with the top bit set to 1) is kernel-space. (Note that x86-64 defines “canonical” “lower half” and “higher half” addresses, with a number of bits effectively limited to 48 or 56; see Wikipedia for details.)



          The complete map is documented in detail in the kernel; currently it looks like



          ===========================================================================================
          Start addr | Offset | End addr | Size | VM area description
          ===========================================================================================
          | | | |
          0000000000000000 | 0 | 00007fffffffffff | 128 TB | user-space virtual memory
          __________________|____________|__________________|_________|______________________________
          | | | |
          0000800000000000 | +128 TB | ffff7fffffffffff | ~16M TB | non-canonical
          __________________|____________|__________________|_________|______________________________
          | | | |
          ffff800000000000 | -128 TB | ffffffffffffffff | 128 TB | kernel-space virtual memory
          __________________|____________|__________________|_________|______________________________


          with 48-bit virtual addresses.



          Unlike the 32-bit case, the “64-bit” memory map is a direct reflection of hardware constraints.






          share|improve this answer















          The 64-bit x86 virtual memory map splits the address space into two: the lower section (with the top bit set to 0) is user-space, the upper section (with the top bit set to 1) is kernel-space. (Note that x86-64 defines “canonical” “lower half” and “higher half” addresses, with a number of bits effectively limited to 48 or 56; see Wikipedia for details.)



          The complete map is documented in detail in the kernel; currently it looks like



          ===========================================================================================
          Start addr | Offset | End addr | Size | VM area description
          ===========================================================================================
          | | | |
          0000000000000000 | 0 | 00007fffffffffff | 128 TB | user-space virtual memory
          __________________|____________|__________________|_________|______________________________
          | | | |
          0000800000000000 | +128 TB | ffff7fffffffffff | ~16M TB | non-canonical
          __________________|____________|__________________|_________|______________________________
          | | | |
          ffff800000000000 | -128 TB | ffffffffffffffff | 128 TB | kernel-space virtual memory
          __________________|____________|__________________|_________|______________________________


          with 48-bit virtual addresses.



          Unlike the 32-bit case, the “64-bit” memory map is a direct reflection of hardware constraints.







          share|improve this answer














          share|improve this answer



          share|improve this answer








          edited 9 hours ago

























          answered 11 hours ago









          Stephen KittStephen Kitt

          179k24406484




          179k24406484












          • To clarify: this limitation is imposed by the hardware. There is currently no 64-bit processor implementation that doesn't leave a huge hole of unusable addresses in the middle of the virtual address space. The amount of physical memory the CPUs are able to address is also way below 2 to the power of 64.

            – Johan Myréen
            9 hours ago











          • Thanks @Johan, I’ve tried to highlight this.

            – Stephen Kitt
            9 hours ago

















          • To clarify: this limitation is imposed by the hardware. There is currently no 64-bit processor implementation that doesn't leave a huge hole of unusable addresses in the middle of the virtual address space. The amount of physical memory the CPUs are able to address is also way below 2 to the power of 64.

            – Johan Myréen
            9 hours ago











          • Thanks @Johan, I’ve tried to highlight this.

            – Stephen Kitt
            9 hours ago
















          To clarify: this limitation is imposed by the hardware. There is currently no 64-bit processor implementation that doesn't leave a huge hole of unusable addresses in the middle of the virtual address space. The amount of physical memory the CPUs are able to address is also way below 2 to the power of 64.

          – Johan Myréen
          9 hours ago





          To clarify: this limitation is imposed by the hardware. There is currently no 64-bit processor implementation that doesn't leave a huge hole of unusable addresses in the middle of the virtual address space. The amount of physical memory the CPUs are able to address is also way below 2 to the power of 64.

          – Johan Myréen
          9 hours ago













          Thanks @Johan, I’ve tried to highlight this.

          – Stephen Kitt
          9 hours ago





          Thanks @Johan, I’ve tried to highlight this.

          – Stephen Kitt
          9 hours ago

















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