efi/x86: Do not clean dummy variable in kexec path

kexec reboot fails randomly in UEFI based KVM guest.  The firmware
just resets while calling efi_delete_dummy_variable();  Unfortunately
I don't know how to debug the firmware, it is also possible a potential
problem on real hardware as well although nobody reproduced it.

The intention of the efi_delete_dummy_variable is to trigger garbage collection
when entering virtual mode.  But SetVirtualAddressMap can only run once
for each physical reboot, thus kexec_enter_virtual_mode() is not necessarily
a good place to clean a dummy object.

Drop the efi_delete_dummy_variable so that kexec reboot can work.

Signed-off-by: Dave Young <[email protected]>
Signed-off-by: Ard Biesheuvel <[email protected]>
Acked-by: Matthew Garrett <[email protected]>
Cc: Ben Dooks <[email protected]>
Cc: Jarkko Sakkinen <[email protected]>
Cc: Jerry Snitselaar <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: Lukas Wunner <[email protected]>
Cc: Lyude Paul <[email protected]>
Cc: Octavian Purdila <[email protected]>
Cc: Peter Jones <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Scott Talbert <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: [email protected]
Cc: [email protected]
Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Ingo Molnar <[email protected]>

Author: daveyoung

arch/x86/platform/efi/efi.c

@@ -917,9 +917,6 @@ static void __init kexec_enter_virtual_mode(void)
 
 	if (efi_enabled(EFI_OLD_MEMMAP) && (__supported_pte_mask & _PAGE_NX))
 		runtime_code_page_mkexec();
-
-	/* clean DUMMY object */
-	efi_delete_dummy_variable();
 #endif
 }