linux-kernel - [PATCH 7/7] efi/x86: do not clean dummy variable in kexec path

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Message-Id: <20191002165904.8819-8-ard.biesheuvel@linaro.org>
Date:   Wed,  2 Oct 2019 18:59:04 +0200
From:   Ard Biesheuvel <ard.biesheuvel@...aro.org>
To:     linux-efi@...r.kernel.org, Ingo Molnar <mingo@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>
Cc:     Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        linux-kernel@...r.kernel.org,
        Ben Dooks <ben.dooks@...ethink.co.uk>,
        Dave Young <dyoung@...hat.com>,
        Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>,
        Jerry Snitselaar <jsnitsel@...hat.com>,
        linux-integrity@...r.kernel.org, Lukas Wunner <lukas@...ner.de>,
        Lyude Paul <lyude@...hat.com>,
        Matthew Garrett <mjg59@...gle.com>,
        Octavian Purdila <octavian.purdila@...el.com>,
        Peter Jones <pjones@...hat.com>, Scott Talbert <swt@...hie.net>
Subject: [PATCH 7/7] efi/x86: do not clean dummy variable in kexec path

From: Dave Young <dyoung@...hat.com>

kexec reboot fails randomly in UEFI based kvm guest.  The firmware
just reset 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 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 dummy object.

Drop efi_delete_dummy_variable so that kexec reboot can work.

Signed-off-by: Dave Young <dyoung@...hat.com>
Acked-by: Matthew Garrett <mjg59@...gle.com>
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@...aro.org>
---
 arch/x86/platform/efi/efi.c | 3 ---
 1 file changed, 3 deletions(-)

diff --git a/arch/x86/platform/efi/efi.c b/arch/x86/platform/efi/efi.c
index c202e1b07e29..425e025341db 100644
--- a/arch/x86/platform/efi/efi.c
+++ b/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
 }
 
-- 
2.20.1