[PATCH v2 2/2] x86/setup: merge several reservations of start of the memory

From: Mike Rapoport <rppt@kernel.org>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: Andrea Arcangeli <aarcange@redhat.com>,
	Baoquan He <bhe@redhat.com>, Borislav Petkov <bp@alien8.de>,
	David Hildenbrand <david@redhat.com>,
	"H. Peter Anvin" <hpa@zytor.com>, Ingo Molnar <mingo@redhat.com>,
	Mel Gorman <mgorman@suse.de>, Michal Hocko <mhocko@kernel.org>,
	Mike Rapoport <rppt@kernel.org>,
	Mike Rapoport <rppt@linux.ibm.com>, Qian Cai <cai@lca.pw>,
	Thomas Gleixner <tglx@linutronix.de>,
	Vlastimil Babka <vbabka@suse.cz>,
	linux-kernel@vger.kernel.org, linux-mm@kvack.org, x86@kernel.org,
	Borislav Petkov <bp@suse.de>
Subject: [PATCH v2 2/2] x86/setup: merge several reservations of start of the memory
Date: Thu, 28 Jan 2021 12:57:11 +0200	[thread overview]
Message-ID: <20210128105711.10428-3-rppt@kernel.org> (raw)
In-Reply-To: <20210128105711.10428-1-rppt@kernel.org>

From: Mike Rapoport <rppt@linux.ibm.com>

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>
Reviewed-by: David Hildenbrand <david@redhat.com>
Acked-by: Borislav Petkov <bp@suse.de>
---
 arch/x86/kernel/setup.c | 28 ++++++++++------------------
 1 file changed, 10 insertions(+), 18 deletions(-)

diff --git a/arch/x86/kernel/setup.c b/arch/x86/kernel/setup.c
index 3b582406363a..b36624e3dc9e 100644
--- a/arch/x86/kernel/setup.c
+++ b/arch/x86/kernel/setup.c
@@ -703,20 +703,6 @@ static int __init parse_reservelow(char *p)
 
 early_param("reservelow", parse_reservelow);
 
-static void __init trim_low_memory_range(void)
-{
-	/*
-	 * A special case is the first 4Kb of memory;
-	 * This is a BIOS owned area, not kernel ram, but generally
-	 * not listed as such in the E820 table.
-	 *
-	 * This typically reserves additional memory (64KiB by default)
-	 * since some BIOSes are known to corrupt low memory.  See the
-	 * Kconfig help text for X86_RESERVE_LOW.
-	 */
-	memblock_reserve(0, ALIGN(reserve_low, PAGE_SIZE));
-}
-
 static void __init early_reserve_memory(void)
 {
 	/*
@@ -729,10 +715,17 @@ 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();
 
@@ -745,7 +738,6 @@ static void __init early_reserve_memory(void)
 	reserve_bios_regions();
 
 	trim_snb_memory();
-	trim_low_memory_range();
 }
 
 /*
-- 
2.28.0

