Using qemu to find out physical address of a given virtual address for Xen

Using qemu to find out physical address of a given virtual address for Xen

Environment: Xen 3.3 32bit PAE is installed as a QEMU virtual machine.
Input: 0xc0100000 (the virtual address of domain 0 kernel)
Output: the physical address of 0xc0100000.

Process:
1. Use "info registers" cmd in qemu monitor to get cr3. cr3 is 0x29cd00. This is the physical base addr of page directory pointer table (PDPT).
2. Get the top two bits of virtual address; it is the index for page directory pointer entry.
For 0xc0100000, the highest btye is 0xc, which is 1100(b). So the index is 11(b) = 3 .
3. The length of one entry of PDPT is 64bits (intel cpu manual 3a,3.8.5) = 8 byte. 3*8=24(d) = 0x18.
4. cr3+0x18 contains the entry for page directory table.
cr3+0x18 = 0x0029cd00+0x18 = 0x0029cd18.
xp /20hx 0x0029cd18 = 0x390b 6001. This is the base addr for page dir table.
5. Bits 21 to 29 of virtual address is the index for page dir table.
For 0xc010000, the top 4 bytes are 1100,0000,0001,0000 (b). Bits 21 to 29 are:00,0000,000(b). That is 0. So the index for page dir table is 0.
6. xp /20hx 0x390b,6000 (the lower byte(s) contains some flags, just ignore them for now.)
The output is 0x3dbc,a067.
7. Bits 20 to 12 of virtual address is the index for page table. (For 2MB pages, it is different)
That is 1,0000, 0000(b), which is 0x100. Since each entry is 8 byte (64bits). The position for page tabe is 0x100*8= 0x800.
8. The lower bits of 0x3dbc, a067 are some flags. Just ignore 067 for now. The physical address for page table is
0x3dbc,a000 + 0x800 = 0x3dbc,a800.
xp /20hx 0x3dbc, a800. The output is 0x3d10,0063. Again, the lower bits are flags. So we get final result: 0x3d10,0000. (I skipped the computation for offset with a page.)

Note: To verify that they are actually point the same data, use "x" and "xp" cmd in qemu monitor to show their content. E.g. x /20hx 0xc0100000 , and xp /20hx 0x3d100000. The output should be the same.

Reference:
Intel 64 and IA-32 Architectures Software Developer’s Manual Volume 3A