Re: [Xen-devel] [PATCH] xen: Add support for dom0 with Linux kernel 3.19 and newer

[David Vrabel]

On 21/01/16 20:13, Daniel Kiper wrote:
> Linux kernel commit 054954eb051f35e74b75a566a96fe756015352c8
> (xen: switch to linear virtual mapped sparse p2m list), which
> appeared in 3.19, introduced linear virtual mapped sparse p2m
> list. If readmem() reads p2m then it access this list using
> physical addresses. Sadly, VMA to physical address translation
> in crash requires access to p2m list. This means that we have
> a chicken and egg problem. In general this issue must be solved
> by introducing some changes in libxl, Linux kernel and crash
> (I have added this task to my long TODO list). However, in dom0
> case we can use crash_xen_info_t.dom0_pfn_to_mfn_frame_list_list
> which is available out of the box. So, let's use it and make
> at least some users happy.

I'm confused.  How does a virtual address to (pseudo-)physical address
lookup require access to the p2m?  Surely this is a walk of the page
tables followed by a M2P lookup on the MFN in the L1 PTE?

David