[tip: x86/boot] x86/setup: Merge several reservations of start of memory

["tip-bot2 for Mike Rapoport" <tip-bot2@linutronix.de>]

The following commit has been merged into the x86/boot branch of tip:

Commit-ID:     4c674481dcf9974834b96622fa4b079c176f36f9
Gitweb:        https://git.kernel.org/tip/4c674481dcf9974834b96622fa4b079c176f36f9
Author:        Mike Rapoport <rppt@linux.ibm.com>
AuthorDate:    Tue, 02 Mar 2021 12:04:06 +02:00
Committer:     Borislav Petkov <bp@suse.de>
CommitterDate: Tue, 23 Mar 2021 17:17:36 +01:00

x86/setup: Merge several reservations of start of memory

Currently, the first several pages are reserved both to avoid leaking
their contents on systems with L1TF and to avoid corrupting BIOS memory.

Merge the two memory reservations.

Signed-off-by: Mike Rapoport <rppt@linux.ibm.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Reviewed-by: David Hildenbrand <david@redhat.com>
Acked-by: Borislav Petkov <bp@suse.de>
Link: https://lkml.kernel.org/r/20210302100406.22059-3-rppt@kernel.org
---
 arch/x86/kernel/setup.c | 19 ++++++++++---------
 1 file changed, 10 insertions(+), 9 deletions(-)

diff --git a/arch/x86/kernel/setup.c b/arch/x86/kernel/setup.c
index 3e3c603..776fc9b 100644
--- a/arch/x86/kernel/setup.c
+++ b/arch/x86/kernel/setup.c
@@ -713,11 +713,6 @@ static int __init parse_reservelow(char *p)
 
 early_param("reservelow", parse_reservelow);
 
-static void __init trim_low_memory_range(void)
-{
-	memblock_reserve(0, ALIGN(reserve_low, PAGE_SIZE));
-}
-
 static void __init early_reserve_memory(void)
 {
 	/*
@@ -730,10 +725,17 @@ static void __init early_reserve_memory(void)
 			 (unsigned long)__end_of_kernel_reserve - (unsigned long)_text);
 
 	/*
-	 * Make sure page 0 is always reserved because on systems with
-	 * L1TF its contents can be leaked to user processes.
+	 * The first 4Kb of memory is a BIOS owned area, but generally it is
+	 * not listed as such in the E820 table.
+	 *
+	 * Reserve the first memory page and typically some additional
+	 * memory (64KiB by default) since some BIOSes are known to corrupt
+	 * low memory. See the Kconfig help text for X86_RESERVE_LOW.
+	 *
+	 * In addition, make sure page 0 is always reserved because on
+	 * systems with L1TF its contents can be leaked to user processes.
 	 */
-	memblock_reserve(0, PAGE_SIZE);
+	memblock_reserve(0, ALIGN(reserve_low, PAGE_SIZE));
 
 	early_reserve_initrd();
 
@@ -746,7 +748,6 @@ static void __init early_reserve_memory(void)
 	reserve_bios_regions();
 
 	trim_snb_memory();
-	trim_low_memory_range();
 }
 
 /*