Date:   Sat, 2 Sep 2017 19:53:50 +0530
From:   Bhupesh Sharma <bhsharma@...hat.com>
To:     Sai Praneeth Prakhya <sai.praneeth.prakhya@...el.com>
Cc:     linux-efi@...r.kernel.org, linux-kernel@...r.kernel.org,
        Matt Fleming <matt@...eblueprint.co.uk>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>, jlee@...e.com,
        Borislav Petkov <bp@...en8.de>, tony.luck@...el.com,
        luto@...nel.org, mst@...hat.com, ricardo.neri@...el.com,
        ravi.v.shankar@...el.com
Subject: Re: [PATCH V2 0/3] Use mm_struct and switch_mm() instead of manually

On Sat, Sep 2, 2017 at 7:38 PM, Bhupesh Sharma <bhsharma@...hat.com> wrote:
> Hi Sai,
>
> On Tue, Aug 29, 2017 at 5:07 AM, Sai Praneeth Prakhya
> <sai.praneeth.prakhya@...el.com> wrote:
>> From: Sai Praneeth <sai.praneeth.prakhya@...el.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.
>>
>> 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       | 52 ++++++++++++++++++++----------------
>>  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, 55 insertions(+), 48 deletions(-)
>>
>> --
>> 2.1.4
>>
>
> Thanks for this v2.
> Introducing the 'efi_switch_mm() ' helper instead of manually
> twiddling with %cr3 seems more cleaner.
>
> I have tested this patchset on a x86_64 machine with the following
> configurations:
>
> 1. Primary kernel boot with efi=old_map
> 2. Primary kernel boot with new efi map
>
> While it seems that efi=old_map passes, the new efi map boot fails for
> me on both the two x86 machine (Dell 3050MT and a SGI - UV300 machine.
>
> It seems we are hitting a NULL pointer deference in
> 'efi_call_phys_prolog' while accessing '&efi_mm'.
>
> Please see the log below for details:
>
> [    0.020006] BUG: unable to handle kernel NULL pointer dereference
> at           (null)
> [    0.021000] IP: switch_mm_irqs_off+0x44/0x270
> [    0.021000] PGD 0
> [    0.021000] P4D 0
> [    0.021000]
> [    0.021000] Oops: 0002 [#1] SMP
> [    0.021000] Modules linked in:
> [    0.021000] CPU: 0 PID: 0 Comm: swapper/0 Not tainted 4.12.0-rc7+ #8
> [    0.021000] Hardware name: SGI UV300/UV300, BIOS SGI UV 300 series
> BIOS 05/25/2016
> [    0.021000] task: ffffffffb0e104c0 task.stack: ffffffffb0e00000
> [    0.021000] RIP: 0010:switch_mm_irqs_off+0x44/0x270
> [    0.021000] RSP: 0000:ffffffffb0e035d0 EFLAGS: 00010083
> [    0.021000] RAX: 0000000000000000 RBX: ffffffffb0fbe620 RCX: ffffffffb0e61348
> [    0.021000] RDX: ffffffffb0e104c0 RSI: ffffffffb0fbe620 RDI: ffffffffb0f14660
> [    0.021000] RBP: ffffffffb0e035f0 R08: 65202c3120676f6c R09: 0000000000000189
> [    0.021000] R10: 30313d6d6d5f6966 R11: 3432303331363936 R12: ffffffffb0f14660
> [    0.021000] R13: 0000000000000000 R14: 0000000000000bb0 R15: 0000000000000450
> [    0.021000] FS:  0000000000000000(0000) GS:ffff8bf2c3600000(0000)
> knlGS:0000000000000000
> [    0.021000] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> [    0.021000] CR2: 0000000000000000 CR3: 0000005b43e09000 CR4: 00000000000406b0
> [    0.021000] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> [    0.021000] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> [    0.021000] Call Trace:
> [    0.021000]  switch_mm+0x20/0x30
> [    0.021000]  efi_switch_mm+0x49/0x60
> [    0.021000]  efi_call_phys_prolog+0x56/0x1b3
> [    0.021000]  efi_enter_virtual_mode+0x3a9/0x520
> [    0.021000]  start_kernel+0x424/0x4c8
> [    0.021000]  ? set_init_arg+0x5a/0x5a
> [    0.021000]  ? early_idt_handler_array+0x120/0x120
> [    0.021000]  x86_64_start_reservations+0x29/0x2b
> [    0.021000]  x86_64_start_kernel+0x151/0x174
> [    0.021000]  secondary_startup_64+0x9f/0x9f
> [    0.021000] Code: 2d 82 51 d9 4f 65 c7 05 0f 65 da 4f 01 00 00 00
> 48 39 f7 0f 84 14 01 00 00 65 48 89 35 f6 64 da 4f 48 8b 86 e8 02 00
> 00 45 89 ed <f0> 4c 0f ab 28 bf 00 00 00 80 48 03 7e 50 48 8b 05 27 b0
> b9 00
> [    0.021000] RIP: switch_mm_irqs_off+0x44/0x270 RSP: ffffffffb0e035d0
> [    0.021000] CR2: 0000000000000000
> [    0.021000] ---[ end trace fb94349305e1cb8b ]---
> [    0.021000] Kernel panic - not syncing: Fatal exception
> [    0.021000] ---[ end Kernel panic - not syncing: Fatal exception
>

And I forgot to mention that I tried the patchset both with the
efi/next and linus's trees and saw the same result.

I would be happy to help in case you need further details of the test
environment or need help in testing this crash further.

Regards,
Bhupesh

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