[G][PATCH 0/1] qemu (secure guest) crash due to gup_fast / dynamic page table folding issue (LP: 1896726)

[frank.heimes at canonical.com]

BugLink: https://bugs.launchpad.net/bugs/1896726

Secure KVM guest (using secure execution on Ubuntu Server 20.04 for s390x)
crashes happen from time to time during boot.
Such crashed guests ("reason=crashed" in the libvirt log) end up in shutoff state
instead of crashed state (<on_crash> preserve is set).
The crash points to a kernel memory management problem, addressed by the following patch/fix.
The modifications touch common memory management code,
but it will have no effect to architectures other than s390x.
This is ensured by the fact that only s390 provides / implements the new helper functions.
And for s390x, this is actually a critical (and carefully tested) fix for a (previous) regression,
so it can hardly get any more regressive.
The patch landed upstream in linux-next, is in depth discussed
at LKML https://lkml.kernel.org/r/20190418100218.0a4afd51@mschwideX1
and here https://lore.kernel.org/linux-arch/patch.git-943f1e5dcff2.your-ad-here.call-01599856292-ext-8676@work.hours/
and will soon land via the regular upstream stable release update for kernel 5.4 in focal, too.
The process already started:
https://lore.kernel.org/stable/patch-1.thread-41918b.git-41918be365c0.your-ad-here.call-01600439945-ext-8991@work.hours/

Hence this cherry-pick from the upstream patch should be added to groovy
to avoid any potential regression in case the patch landed in focal via the upstream release update process,
but is not in groovy and someones upgrades from focal to groovy.

Vasily Gorbik (1):
  From: Vasily Gorbik <gor at linux.ibm.com>

 arch/s390/include/asm/pgtable.h | 42 +++++++++++++++++++++++----------
 include/linux/pgtable.h         | 10 ++++++++
 mm/gup.c                        | 18 +++++++-------
 3 files changed, 49 insertions(+), 21 deletions(-)

-- 
2.25.1