Re: [PATCH 07/12] x86/virt/guest/xen: Remove use of pgd_list from the Xen guest code

From: Boris Ostrovsky
Date: Tue Jun 16 2015 - 10:21:17 EST

On 06/16/2015 10:15 AM, David Vrabel wrote:
On 15/06/15 21:35, Ingo Molnar wrote:
* David Vrabel <david.vrabel@xxxxxxxxxx> wrote:

On 15/06/15 10:05, Ian Campbell wrote:
On Sat, 2015-06-13 at 11:49 +0200, Ingo Molnar wrote:
xen_mm_pin_all()/unpin_all() are used to implement full guest instance
suspend/restore. It's a stop-all method that needs to iterate through all
allocated pgds in the system to fix them up for Xen's use.

This code uses pgd_list, probably because it was an easy interface.

But we want to remove the pgd_list, so convert the code over to walk all
tasks in the system. This is an equivalent method.
It is not equivalent because pgd_alloc() now populates entries in pgds that are
not visible to xen_mm_pin_all() (note how the original code adds the pgd to the
pgd_list in pgd_ctor() before calling pgd_prepopulate_pmd()). These newly
allocated page tables won't be correctly converted on suspend/resume and the new
process will die after resume.
So how should the Xen logic be fixed for the new scheme? I can't say I can see
through the paravirt complexity here.
Actually, since we freeze_processes() before trying to pin page tables,
I think it should be ok as-is.

I'll put the patch through some tests.

Actually, I just ran this through a couple of boot/suspend/resume tests and didn't see any issues (with the one fix I mentioned to Ingo earlier). On unstable Xen only.


To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at
Please read the FAQ at