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Extended Feature Enable Register (EFER) is a model-specific register added in the AMD K6 processor, to allow enabling the SYSCALL/SYSRET instruction, and later for entering and exiting long mode. This register becomes architectural in AMD64 and has been adopted by Intel as IA32_EFER.
In protected mode with paging enabled (bit 31, PG, of control register CR0 is set), but without PAE, x86 processors use a two-level page translation scheme. Control register CR3 holds the page-aligned physical address of a single 4 KB long page directory .
In traditional 32-bit protected mode, x86 processors use a two-level page translation scheme, where the control register CR3 points to a single 4 KiB-long page directory, which is divided into 1024 × 4-byte entries that point to 4 KiB-long page tables, similarly consisting of 1024 × 4-byte entries pointing to 4 KiB-long pages.
In computing, protected mode, also called protected virtual address mode, [1] is an operational mode of x86-compatible central processing units (CPUs). It allows system software to use features such as segmentation, virtual memory, paging and safe multi-tasking designed to increase an operating system's control over application software.
If paging is not enabled, these linear addresses are the same as physical addresses. Note that when paging is enabled, different tasks may have different linear-to-physical address mappings. When this is the case, an address in a debug address register may be relevant to one task but not to another.
With hardware TLB management, the CPU automatically walks the page tables (using the CR3 register on x86, for instance) to see whether there is a valid page-table entry for the specified virtual address. If an entry exists, it is brought into the TLB, and the TLB access is retried: this time the access will hit, and the program can proceed ...
Moves to the CR3 control register are serializing and will flush the TLB. [l] On Pentium and later processors, moves to the CR0 and CR4 control registers are also serializing. [m] MOV reg,DRx: 0F 21 /r [j] Move from x86 debug register to general register. [k] MOV DRx,reg: 0F 23 /r [j] Move from general register to x86 debug register. [k]
Second Level Address Translation (SLAT), also known as nested paging, is a hardware-assisted virtualization technology which makes it possible to avoid the overhead associated with software-managed shadow page tables.