From fb1d9d3f95654f00c4156129f3cd90d3efe32d26 Mon Sep 17 00:00:00 2001
From: Jiri Kosina <jkosina@suse.cz>
Date: Wed, 25 Jan 2017 20:52:33 +0100
Subject: [PATCH] x86/efi: always map first physical page into EFI pagetables
Commit 129766708 ("x86/efi: Only map RAM into EFI page tables if in
mixed-mode") stopped creating 1:1 mapping for all RAM in case of running
in native 64bit mode.
It turns out though that there are 64bit EFI implementations in the wild
(this particular problem has been reported on Lenovo Yoga 710-11IKB) which
still make use of first physical page for their own private use (which is
what legacy BIOS used to do, but EFI specification doesn't grant any such
right to EFI BIOS ... oh well).
In case there is no mapping for this particular frame in EFI pagetables,
as soon as firmware tries to make use of it, triple fault occurs and the
system reboots (in case of Yoga 710-11IKB this is very early during boot).
Fix that by always mapping the first page of physical memory into EFI
pagetables.
Note: just reverting 129766708 is not enough on v4.9-rc1+ to fix the
regression on affected hardware, as commit ab72a27da ("x86/efi:
Consolidate region mapping logic") later made the first physical frame not
to be mapped anyway.
Fixes: 129766708 ("x86/efi: Only map RAM into EFI page tables if in mixed-mode")
Cc: stable@kernel.org # v4.8+
Cc: Waiman Long <waiman.long@hpe.com>
Cc: Borislav Petkov <bp@suse.de>
Cc: Laura Abbott <labbott@redhat.com>
Cc: Vojtech Pavlik <vojtech@ucw.cz>
Reported-by: Hanka Pavlikova <hanka@ucw.cz>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>
---
arch/x86/platform/efi/efi_64.c | 11 +++++++++++
1 file changed, 11 insertions(+)
diff --git a/arch/x86/platform/efi/efi_64.c b/arch/x86/platform/efi/efi_64.c
index 319148bd4b05..02ae2abe8b8e 100644
--- a/arch/x86/platform/efi/efi_64.c
+++ b/arch/x86/platform/efi/efi_64.c
@@ -269,6 +269,17 @@ int __init efi_setup_page_tables(unsigned long pa_memmap, unsigned num_pages)
efi_scratch.use_pgd = true;
/*
+ * Certain firmware versions are way too sentimental and still believe
+ * they are exclusive and unquestionable owners of first physical page.
+ * Create 1:1 mapping for this page to avoid triple faults during early
+ * boot with such firmware.
+ */
+ if (kernel_map_pages_in_pgd(pgd, 0x0, 0x0, 1, _PAGE_RW)) {
+ pr_err("Failed to create 1:1 mapping of first page\n");
+ return 1;
+ }
+
+ /*
* When making calls to the firmware everything needs to be 1:1
* mapped and addressable with 32-bit pointers. Map the kernel
* text and allocate a new stack because we can't rely on the
--
2.11.0