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include vmm.inc
 
VMMcall _ModifyPageBits, <VM, VMLinPgNum, nPages, bitAND, bitOR,
                          pType, flags>
 
or      eax, eax            ; nonzero if modified, zero if error
jz      not_modified
 
The _ModifyPageBits service modifies the page attribute bits associated with
PG_HOOKED pages in the V86 address space of a virtual machine. Virtual
devices use this service to modify the P_PRES, P_WRITE, and P_USER bits and
the PG_TYPE, if appropriate.
 
Parameter   Description
────────────────────────────────────────────────────────────────────────────
 
VM          Specifies a handle identifying the virtual machine owning the
            pages to modify.
 
VMLinPgNum  Specifies the linear page number of the first page to modify.
            All pages must be in the 1 megabyte V86 address space. Page
            numbers below the first page of the specified virtual machine or
            above 10Fh cause an error.
 
nPages      Specifies the number of pages to modify.
 
bitAND      Specifies the AND mask for the page attribute bits. All AND mask
            bits, except the P_PRES, P_WRITE, and P_USER bits, must be set
            to 1. The P_PRES, P_WRITE, and P_USER bits can be 0 or 1 to
            clear or preserve the corresponding page attributes.
 
bitOR       Specifies the OR mask for the page attribute bits. All bits,
            except the P_PRES, P_WRITE, and P_USER bits, must be set to 0.
            The P_PRES, P_WRITE, and P_USER bits can be 0 or 1 to preserve
            or set the corresponding page attributes.
 
pType       Specifies the page type. It can be one of the following values:
 
            Value      Meaning
            ────────────────────────────────────────────────────────────────
            PG_HOOKED  Changes the page type to hooked. This value must be
                       specified if the service clears any one of the
                       P_PRES, P_WRITE and P_USER bits.
 
            PG_IGNORE  Leaves the current page type unchanged.
 
            All other values are reserved.
 
flags       Specifies the operation flags. This parameter must be set to 0.
 
Return Value
 
The EAX register contains a nonzero value if the service is successful.
Otherwise, EAX contains zero to indicate an error such as an invalid virtual
machine handle, invalid bits in AND and OR masks, an invalid type, or a bad
page range.
 
Comments
 
This service always clears the P_DIRTY and P_ACC bits regardless of the AND
and OR mask values.
 
If a virtual device clears the P_PRES, P_WRITE, or P_USER bits, the virtual
device must set the page type for all such pages to PG_HOOKED. Also the
virtual device must have previously installed a hook page fault handler for
these pages.
 
This service cannot be used to set the P_PRES bit. Virtual devices can use
the _MapIntoV86 or _PhysIntoV86 service to make pages present. Since the
_MapIntoV86 service resets the page type to the same page type as the memory
specified by the memory handle, the virtual devices should set the page type
to PG_HOOKED when it creates the memory handle using the _PageAllocate
service. Since the _PhysIntoV86 service sets the page type to PG_SYS, the
virtual devices must use the _ModifyPageBits service to change the page type
to PG_HOOKED if it uses _PhysIntoV86 to map physical pages into a hooked
page region.
 
If using the P_WRITE bit to simulate ROM in a virtual machine, a virtual
device should map the pages using the _PhysIntoV86 service and immediately
call the _ModifyPageBits service to clear the P_WRITE bit and change the
page type to PG_HOOKED.
 
Uses
 
EAX
 
See Also
 
_MapIntoV86, _PhysIntoV86
 
 
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