Re: [PATCH] x86/efi: Fix kexec kernel panic when efi=old_map is enabled

[Dave Young]

On 05/15/17 at 02:23pm, Matt Fleming wrote:
> (Pulling in Dave, Mr. Kexec on EFI)
> 
> On Mon, 08 May, at 12:25:23PM, Sai Praneeth Prakhya wrote:
> > From: Sai Praneeth <sai.praneeth.prakhya@xxxxxxxxx>
> > 
> > Booting kexec kernel with "efi=old_map" in kernel command line hits
> > kernel panic as shown below.
> > 
> > [    0.001000] BUG: unable to handle kernel paging request at ffff88007fe78070
> > [    0.001000] IP: virt_efi_set_variable.part.7+0x63/0x1b0
> > [    0.001000] PGD 7ea28067
> > [    0.001000] PUD 7ea2b067
> > [    0.001000] PMD 7ea2d067
> > [    0.001000] PTE 0
> > [    0.001000]
> > [    0.001000] Oops: 0000 [#1] SMP
> > [    0.001000] Modules linked in:
> > [    0.001000] CPU: 0 PID: 0 Comm: swapper/0 Not tainted 4.11.0-rc2-yocto-standard+ #229
> > [    0.001000] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 0.0.0 02/06/2015
> > [    0.001000] task: ffffffff82022500 task.stack: ffffffff82000000
> > [    0.001000] RIP: 0010:virt_efi_set_variable.part.7+0x63/0x1b0
> > [    0.001000] RSP: 0000:ffffffff82003dc0 EFLAGS: 00010246
> > [    0.001000] RAX: ffff88007fe78018 RBX: ffffffff82050300 RCX: 0000000000000007
> > [    0.001000] RDX: ffffffff82003e50 RSI: ffffffff82050300 RDI: ffffffff82050300
> > [    0.001000] RBP: ffffffff82003e08 R08: 0000000000000000 R09: 0000000000000000
> > [    0.001000] R10: 0000000000000000 R11: 0000000000000000 R12: ffffffff82003e50
> > [    0.001000] R13: 0000000000000007 R14: 0000000000000246 R15: 0000000000000000
> > [    0.001000] FS:  0000000000000000(0000) GS:ffff88007fa00000(0000) knlGS:0000000000000000
> > [    0.001000] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> > [    0.001000] CR2: ffff88007fe78070 CR3: 000000007da1d000 CR4: 00000000000006b0
> > [    0.001000] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> > [    0.001000] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> > [    0.001000] Call Trace:
> > [    0.001000]  virt_efi_set_variable+0x5d/0x70
> > [    0.001000]  efi_delete_dummy_variable+0x7a/0x80
> > [    0.001000]  efi_enter_virtual_mode+0x3f6/0x4a7
> > [    0.001000]  start_kernel+0x375/0x400
> > [    0.001000]  x86_64_start_reservations+0x2a/0x2c
> > [    0.001000]  x86_64_start_kernel+0x168/0x176
> > [    0.001000]  start_cpu+0x14/0x14
> > [    0.001000] Code: 04 b0 84 ff 80 3d c5 56 b3 00 00 4c 8b 44 24 08 75
> > 6b 9c 41 5e 48 8b 05 9c 78 99 00 4d 89 c1 48 89 de 4d 89 f8 44 89 e9 4c
> > 89 e2 <48> 8b 40 58 48 8b 78 58 e8 b0 2d 88 ff 48 c7 c6 b6 1d f4 81 4c
> > [    0.001000] RIP: virt_efi_set_variable.part.7+0x63/0x1b0 RSP: ffffffff82003dc0
> > [    0.001000] CR2: ffff88007fe78070
> > [    0.001000] ---[ end trace 0000000000000000 ]---
> > [    0.001000] Kernel panic - not syncing: Attempted to kill the idle task!
> > [    0.001000] ---[ end Kernel panic - not syncing: Attempted to kill the idle task!
> > 
> > This happens because efi=old_map doesn't use efi_pgd but rather it uses
> > kernel's pgd. We don't hit the same panic in a regular kernel because
> > it uses old_map_region() and not __map_region().
> > 
> > Signed-off-by: Sai Praneeth Prakhya <sai.praneeth.prakhya@xxxxxxxxx>
> > Cc: Borislav Petkov <bp@xxxxxxxxx>
> > Cc: Ricardo Neri <ricardo.neri@xxxxxxxxx>
> > Cc: Matt Fleming <matt@xxxxxxxxxxxxxxxxxxx>
> > Cc: Ard Biesheuvel <ard.biesheuvel@xxxxxxxxxx>
> > Cc: Ravi Shankar <ravi.v.shankar@xxxxxxxxx>
> > ---
> >  arch/x86/platform/efi/efi_64.c | 3 +++
> >  1 file changed, 3 insertions(+)
> > 
> > diff --git a/arch/x86/platform/efi/efi_64.c b/arch/x86/platform/efi/efi_64.c
> > index 4e043a8c8556..76e1cd6b74dd 100644
> > --- a/arch/x86/platform/efi/efi_64.c
> > +++ b/arch/x86/platform/efi/efi_64.c
> > @@ -320,6 +320,9 @@ static void __init __map_region(efi_memory_desc_t *md, u64 va)
> >  	unsigned long pfn;
> >  	pgd_t *pgd = efi_pgd;
> >  
> > +	if (efi_enabled(EFI_OLD_MEMMAP))
> > +		pgd = swapper_pg_dir;
> > +
> >  	if (!(md->attribute & EFI_MEMORY_WB))
> >  		flags |= _PAGE_PCD;
> >  
> 
> The thing is, efi=old_map was never intended to work with kexec.
> 
> Part of the reason for introducing the new EFI runtime services
> mapping scheme was so that we could kexec on EFI. See commit
> d2f7cbe7b26a ("x86/efi: Runtime services virtual mapping").
> 
> The problem with using efi=old_map is that the virtual addresses are
> assigned from the memory region used by other kernel mappings;
> vmalloc() space.
> 
> Potentially there could be collisions when booting kexec if something
> else is mapped at the virtual address we allocated for runtime service
> regions in the initial boot.
> 
> So, while this patch may work for you and Joey, I don't think it's
> reliable.
> 
> Dave, did I miss anything?

Matt, sorry for late reply, I did not notice this patch is kexec related
and I missed it.

Yes, you are right, efi=old_map is supposed not to work with kexec
reboot because the runtime va is not persistent. The only way for
old_map kexec boot is use below kexec-tools option to load kexec kernel:
kexec --noefi
and at the same time need pass acpi root pointer in kexec kernel
cmdline:
acpi_rsdp=<acpi rsdp addr, see /sys/firmware/efi/systab>

Thanks
Dave