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Subject[PATCH V4 0/3] Use mm_struct and switch_mm() instead of manually
From: Sai Praneeth <>

Presently, in x86, to invoke any efi function like
efi_set_virtual_address_map() or any efi_runtime_service() the code path
typically involves read_cr3() (save previous pgd), write_cr3()
(write efi_pgd) and calling efi function. Likewise after returning from
efi function the code path typically involves read_cr3() (save efi_pgd),
write_cr3() (write previous pgd). We do this couple of times in efi
subsystem of Linux kernel, instead we can use helper function
efi_switch_mm() to do this. This improves readability and maintainability.
Also, instead of maintaining a separate struct "efi_scratch" to store/restore
efi_pgd, we can use mm_struct to do this.

I have tested this patch set against LUV (Linux UEFI Validation), so I
think I didn't break any existing configurations. I have tested this
patch set for
1. x86_64,
2. x86_32,
3. Mixed mode
with efi=old_map and for kexec kernel. Please let me know if I have
missed any other configurations.

Changes in V2:
1. Resolve mm_dropping() issue by not mm_dropping()/mm_grabbing() any mm,
as we are not losing/creating any references.

Changes in V3:
1. When CPUMASK_OFFSTACK is enabled, switch_mm_irqs_off() sets cpumask
by calling cpumask_set_cpu(). This panics kernel as efi_mm is not
initialized, therefore initialize efi_mm in efi_alloc_page_tables().

Changes in V4:
1. Remove the unintended removal of local_irq_restore(flags) (in 3rd patch).
IRQ flags should be restored after switching to orginal mm.

This patch set is based on Linus's tree v4.15-rc8

Sai Praneeth (3):
efi: Use efi_mm in x86 as well as ARM
x86/efi: Replace efi_pgd with efi_mm.pgd
x86/efi: Use efi_switch_mm() rather than manually twiddling with %cr3

arch/x86/include/asm/efi.h | 29 +++++++++---------
arch/x86/platform/efi/efi_64.c | 58 +++++++++++++++++++-----------------
arch/x86/platform/efi/efi_thunk_64.S | 2 +-
drivers/firmware/efi/arm-runtime.c | 9 ------
drivers/firmware/efi/efi.c | 9 ++++++
include/linux/efi.h | 2 ++
6 files changed, 57 insertions(+), 52 deletions(-)

Signed-off-by: Sai Praneeth Prakhya <>
Cc: Lee, Chun-Yi <>
Cc: Borislav Petkov <>
Cc: Tony Luck <>
Cc: Andy Lutomirski <>
Cc: Michael S. Tsirkin <>
Cc: Ricardo Neri <>
Cc: Matt Fleming <>
Cc: Ard Biesheuvel <>
Cc: Ravi Shankar <>
Tested-by: Bhupesh Sharma <>


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