Hopefully correct backports for gntdev deadlock

Subject: Hopefully correct backports for gntdev deadlock
From: Demi Marie Obenour <demi@xxxxxxxxxxxxxxxxxxxxxx>
Date: Thu, 30 Jun 2022 20:09:47 -0400
Cc: stable@xxxxxxxxxxxxxxx, Xen developer discussion <xen-devel@xxxxxxxxxxxxxxxxxxxx>
Feedback-id: iac594737:Fastmail

This backports "xen/gntdev: Avoid blocking in unmap_grant_pages()" to
the various stable trees, hopefully correctly.

Follow-Ups:
- Re: Hopefully correct backports for gntdev deadlock
  - From: Juergen Gross
- [PATCH 4.9] xen/gntdev: Avoid blocking in unmap_grant_pages()
  - From: Demi Marie Obenour
- [PATCH 5.10] xen/gntdev: Avoid blocking in unmap_grant_pages()
  - From: Demi Marie Obenour
- [PATCH 5.4] xen/gntdev: Avoid blocking in unmap_grant_pages()
  - From: Demi Marie Obenour
- [PATCH 4.14] xen/gntdev: Avoid blocking in unmap_grant_pages()
  - From: Demi Marie Obenour
- [PATCH 4.19] xen/gntdev: Avoid blocking in unmap_grant_pages()
  - From: Demi Marie Obenour