Re: [PATCH V4 0/3] Use mm_struct and switch_mm() instead of manually

[Ard Biesheuvel]

On 29 January 2018 at 10:51, Ard Biesheuvel  wrote:
> On 26 January 2018 at 21:16, Matt Fleming  wrote:
>> On Thu, 18 Jan, at 01:01:04PM, Sai Praneeth Prakhya wrote:
>>> 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.
>>
>> FWIW this series looks OK to me.
>>
>> Reviewed-by: Matt Fleming 
>
> Thanks Matt
>
> I know the x86 guys have been rather busy lately, so I will give them
> some more time to respond. If there are no objections raised, I will
> queue it for v4.17 in a couple of weeks.

Queued in linux-efi/next

Thanks all.
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Re: [PATCH V4 0/3] Use mm_struct and switch_mm() instead of manually

[Ard Biesheuvel]

On 26 January 2018 at 21:16, Matt Fleming  wrote:
> On Thu, 18 Jan, at 01:01:04PM, Sai Praneeth Prakhya wrote:
>> 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.
>
> FWIW this series looks OK to me.
>
> Reviewed-by: Matt Fleming 

Thanks Matt

I know the x86 guys have been rather busy lately, so I will give them
some more time to respond. If there are no objections raised, I will
queue it for v4.17 in a couple of weeks.
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Re: [PATCH V4 0/3] Use mm_struct and switch_mm() instead of manually

[Matt Fleming]

On Thu, 18 Jan, at 01:01:04PM, Sai Praneeth Prakhya wrote:
> 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.
 
FWIW this series looks OK to me.

Reviewed-by: Matt Fleming 
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[PATCH V4 0/3] Use mm_struct and switch_mm() instead of manually

[Sai Praneeth Prakhya]

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.

Note:
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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