[Xen-devel] Questions on EPT dump and creation

[YAO <yffbrave@xxxxxxxxx>]

First, I used "xm debug-key D" to dump ept mappings. But I have a doubt about the mapping.

I started a 32bit HVM which memory is 512, so the max gfn should be 0x1ffff. But the result of "xm dmesg" showed gfn->mfn mapping until 0xfffff.

Output looked like below:

(XEN) gfn: fc012  mfn: 179e6

(XEN) gfn: fc013  mfn: 179e5

(XEN) gfn: fee00  mfn: 2e8

(XEN) gfn: feffb  mfn: 178fd

(XEN) gfn: feffc  mfn: 178fc

(XEN) gfn: feffd  mfn: 178fb

(XEN) gfn: feffe  mfn: 178fa

(XEN) gfn: fefff  mfn: 178f9

(XEN) gfn: fffff  mfn: 2eb

What I think is every HVM has one EPT table and the table maps the allocated memory like from 0 to 0x1ffff, why does the HVM ept map all the 4G space?

Isn't it unneccessary and waste of memory?

Second, I want to copy the system ept and used the copy for later translation. Since the HVM is 512M, so I need one PML4 pointed by eptp, one PDP pointed by PML4 entry[0], one PD pointed by PDP entry[0], 512 PT's pointed by all PD entries. After all settings are done, I'v got gfn->mfn mapping of 1G memory. I think it should be working, but not. Where am I wrong? What would I pay attention to?

Looking forward to your help,

Yao

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