KnVmAllocate()

This function is declared in the coresrv/vmm/vmm_api.h file.

void *KnVmAllocate(void *addr, rtl_size_t size, int flags);

Reserves a range of physical pages defined by the addr and size parameters. If the VMM_FLAG_COMMIT flag is indicated, the function reserves and commits pages for one call.

Parameters:

• addr is the page-aligned base physical address; if addr is set equal to 0, the system chooses a free area of physical memory.
• size is the size of the memory area in bytes (must be a multiple of the page size).
• flags refers to allocation flags.

Returns the base virtual address of the reserved area. If it is not possible to reserve a memory area, the function returns RTL_NULL.

Allocation flags

In the flags parameter, you can use the following flags (vmm/flags.h):

• VMM_FLAG_RESERVE is a required flag.
• VMM_FLAG_COMMIT lets you reserve and commit memory pages to one KnVmAllocate() call in so-called "lazy" mode.
• VMM_FLAG_LOCKED is used together with VMM_FLAG_COMMIT and lets you immediately commit physical memory pages instead of "lazy" commitment.
• VMM_FLAG_WRITE_BACK, VMM_FLAG_WRITE_THROUGH, VMM_FLAG_WRITE_COMBINE, VMM_FLAG_CACHE_DISABLE and VMM_FLAG_CACHE_MASK manage caching of memory pages.
• VMM_FLAG_READ, VMM_FLAG_WRITE, VMM_FLAG_EXECUTE and VMM_FLAG_RWX_MASK are memory protection attributes.
• VMM_FLAG_LOW_GUARD and VMM_FLAG_HIGH_GUARD add a protective page before and after the allocated memory, respectively.
• VMM_FLAG_GROW_DOWN  defines the direction of memory access (from older addresses to newer addresses).

Permissible combinations of memory protection attributes:

• VMM_FLAG_READ allows reading page contents.
• VMM_FLAG_READ | VMM_FLAG_WRITE allows reading and modifying page contents.
• VMM_FLAG_READ | VMM_FLAG_EXECUTE allows reading and executing page contents.
• VMM_FLAG_RWX_MASK or VMM_FLAG_READ | VMM_FLAG_WRITE | VMM_FLAG_EXECUTE refers to full access to page contents (these entries are equivalent).

Example

coredump->base = KnVmAllocate(RTL_NULL, vmaSize,

VMM_FLAG_READ | VMM_FLAG_RESERVE |

VMM_FLAG_WRITE | VMM_FLAG_COMMIT |

VMM_FLAG_LOCKED).

The KnVmProtect() function can be used to modify the defined memory area protection attributes if necessary.

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