[PATCH v4 0/4] x86/mm: Fix some issues with using trampoline_pgd

[Joerg Roedel <joro@8bytes.org>]

From: Joerg Roedel <jroedel@suse.de>

Hi

here are a couple of fixes and documentation improvements for the use of
the trampoline_pgd in the kernel. Most importantly it fixes the issue
that switching to the trampoline_pgd will unmap the kernel stack and
real_mode_header, making crashes likely before the code can actually
jump to real mode.

The first patch adds a comment to document that the trampoline_pgd
aliases kernel page-tables in the user address range, establishing
global TLB entries for these addresses. The next two patches add
global TLB flushes when switching to and from the trampoline_pgd.

The last patch extends the trampoline_pgd to cover the whole kernel
address range. This is needed to make sure the stack and the
real_mode_header are still mapped after the switch and that the code
flow can safely reach real-mode.

Please review.

Thanks,

	Joerg

Changes v3->v4:

	- Rebased to latest tip/master
	- Addressed Boris' review comments

Link to v3: https://lore.kernel.org/all/20211001154817.29225-1-joro@8bytes.org/

Joerg Roedel (4):
  x86/realmode: Add comment for Global bit usage in trampline_pgd
  x86/mm/64: Flush global TLB on boot and AP bringup
  x86/mm: Flush global TLB when switching to trampoline page-table
  x86/64/mm: Map all kernel memory into trampoline_pgd

 arch/x86/include/asm/realmode.h |  1 +
 arch/x86/include/asm/tlbflush.h |  5 +++++
 arch/x86/kernel/head64.c        |  2 ++
 arch/x86/kernel/head_64.S       | 19 ++++++++++++++++-
 arch/x86/kernel/reboot.c        | 12 ++---------
 arch/x86/mm/init.c              |  5 +++++
 arch/x86/mm/tlb.c               |  8 ++-----
 arch/x86/realmode/init.c        | 38 ++++++++++++++++++++++++++++++++-
 8 files changed, 72 insertions(+), 18 deletions(-)


base-commit: b6c28e3cc445bf451a516ac075ec27b4619e4f5f
-- 
2.34.0