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HvExtCallGetBootZeroedMemory

  • Article

The hypercall returns ranges that are known to be zeroed at the time the hypercall is made. Cacheable reads from reported ranges must return all zeroes.

Querying zeroed ranges may allow the virtual machine to avoid zeroing memory that was already zeroed by the hypervisor.

Ranges can include memory that don’t exist and can overlap. The hypervisor should attempt to report "best" / biggest zeroed ranges earlier in the list for optimal performance.

Interface

HV_STATUS
HvExtCallGetBootZeroedMemory(
   _Out_ PUINT64 RangeCount,
   _Out_ HV_EXT_OUTPUT_BOOT_ZEROED_MEMORY_RANGE Ranges[]
   );

Call Code

0x8002 (Simple)

Output Parameters

The hypercall output size is 0xFF8 bytes.

The first 8 bytes in the output indicates the number of zeroed ranges in the rest of the output. At most 255 ranges can be returned.

Each subsequent 16 bytes indicates a zeroed range. The first 8 bytes indicates the start guest physical page number of the range, the next 8 bytes indicates the total number of pages in the range.

Name Offset Size Information Provided
RangeCount 0 8 Number of returned ranges
Range 0 StartGpa 8 8 Start GPA page number of the first range
Range 0 PageCount 16 8 Page count of the first range
...
Range 254 StartGpa 4072 8 Start GPA page number of the last range
Range 254 PageCount 4080 8 Page count of the last range