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

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

[Sai Praneeth Prakhya]

From: Sai Praneeth <sai.praneeth.prakhya@intel.com>

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().

Note:
This patch set is based on Linus's tree v4.15-rc3

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       | 59 +++++++++++++++++++-----------------
 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(+), 53 deletions(-)

Signed-off-by: Sai Praneeth Prakhya <sai.praneeth.prakhya@intel.com>
Cc: Lee, Chun-Yi <jlee@suse.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Tony Luck <tony.luck@intel.com>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Michael S. Tsirkin <mst@redhat.com>
Cc: Ricardo Neri <ricardo.neri@intel.com>
Cc: Matt Fleming <matt@codeblueprint.co.uk>
Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Cc: Ravi Shankar <ravi.v.shankar@intel.com>
Tested-by: Bhupesh Sharma <bhsharma@redhat.com>

-- 
2.1.4

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

[Bhupesh Sharma]

Hi Sai,

On Sun, Dec 17, 2017 at 5:35 AM, Sai Praneeth Prakhya
<sai.praneeth.prakhya@intel.com> wrote:
> From: Sai Praneeth <sai.praneeth.prakhya@intel.com>
>
> 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().

Thanks for the v3.

I confirmed that the issue I saw with the v2 when I enabled
'efi=debug' on the sgi-uv 300 machine (i.e the NULL pointer access
while accessing mm_cpumask(next), in the function call
'switch_mm_irqs_off') is fixed in the v3.

Also as I noted during the v2 review, introducing the 'efi_switch_mm()
' helper instead of manually
twiddling with %cr3 seems more cleaner (having personally debugged
this leg several times on the underlying x86 EFI machines).

So in addition to me testing this on the sgi-uv300 and Dell Optiplex
EFI enabled machine, please feel free to add:

Reviewed-by: Bhupesh Sharma <bhsharma@redhat.com>

Thanks,
Bhupesh


> Note:
> This patch set is based on Linus's tree v4.15-rc3
>
> 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       | 59 +++++++++++++++++++-----------------
>  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(+), 53 deletions(-)
>
> Signed-off-by: Sai Praneeth Prakhya <sai.praneeth.prakhya@intel.com>
> Cc: Lee, Chun-Yi <jlee@suse.com>
> Cc: Borislav Petkov <bp@alien8.de>
> Cc: Tony Luck <tony.luck@intel.com>
> Cc: Andy Lutomirski <luto@kernel.org>
> Cc: Michael S. Tsirkin <mst@redhat.com>
> Cc: Ricardo Neri <ricardo.neri@intel.com>
> Cc: Matt Fleming <matt@codeblueprint.co.uk>
> Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
> Cc: Ravi Shankar <ravi.v.shankar@intel.com>
> Tested-by: Bhupesh Sharma <bhsharma@redhat.com>
>
> --
> 2.1.4
>
> --
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RE: [PATCH 0/3] Use mm_struct and switch_mm() instead of manually

[Prakhya, Sai Praneeth]

> > 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().
> 
> Thanks for the v3.
> 
> I confirmed that the issue I saw with the v2 when I enabled 'efi=debug' on the
> sgi-uv 300 machine (i.e the NULL pointer access while accessing
> mm_cpumask(next), in the function call
> 'switch_mm_irqs_off') is fixed in the v3.
> 
> Also as I noted during the v2 review, introducing the 'efi_switch_mm() ' helper
> instead of manually twiddling with %cr3 seems more cleaner (having personally
> debugged this leg several times on the underlying x86 EFI machines).
> 
> So in addition to me testing this on the sgi-uv300 and Dell Optiplex EFI enabled
> machine, please feel free to add:
> 
> Reviewed-by: Bhupesh Sharma <bhsharma@redhat.com>
> 

Hi  Bhupesh,

Thanks for the review and re-iterating the usefulness of this patch set.

Regards,
Sai

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

[Sai Praneeth Prakhya]

From: Sai Praneeth <sai.praneeth.prakhya@intel.com>

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, so we can use a 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, 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.

Special thanks to Matt for his initial review.

Matt,
I have implemented efi_switch_mm() in "arch/x86/platform/efi/efi_64.c"
because it's used only by x86_64. Please let me know if you think it
should be in "drivers/firmware/efi/efi.c"

Andy and Michael,
As I am twiddling with memory management for the first time and I think
you are mm experts, could you please review efi_switch_mm() function
in "x86/efi: Use efi_switch_mm() rather than manually twiddling with cr3"

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           | 30 +++++++++----------
 arch/x86/platform/efi/efi_64.c       | 57 ++++++++++++++++++++++--------------
 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, 62 insertions(+), 47 deletions(-)

-- 
2.1.4