x86/sev: Make sure IRQs are disabled while GHCB is active

x86/sev: Make sure IRQs are disabled while GHCB is active

BugLink: https://bugs.launchpad.net/bugs/1938340
[ Upstream commit d187f217335dba2b49fc9002aab2004e04acddee ]

The #VC handler only cares about IRQs being disabled while the GHCB is
active, as it must not be interrupted by something which could cause
another #VC while it holds the GHCB (NMI is the exception for which the
backup GHCB exits).

Make sure nothing interrupts the code path while the GHCB is active
by making sure that callers of __sev_{get,put}_ghcb() have disabled
interrupts upfront.

 [ bp: Massage commit message. ]

Signed-off-by: Joerg Roedel <jroedel@suse.de>
Signed-off-by: Borislav Petkov <bp@suse.de>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20210618115409.22735-2-joro@8bytes.org
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Kamal Mostafa <kamal@canonical.com>
Signed-off-by: Stefan Bader <stefan.bader@canonical.com>