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From:   Mike Rapoport <rppt@kernel.org>
To:     x86@kernel.org
Cc:     Andrew Morton <akpm@linux-foundation.org>,
        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, Borislav Petkov <bp@suse.de>
Subject: [PATCH v3 2/2] x86/setup: merge several reservations of start of the memory
Date:   Tue,  2 Mar 2021 12:04:06 +0200
Message-Id: <20210302100406.22059-3-rppt@kernel.org>
In-Reply-To: <20210302100406.22059-1-rppt@kernel.org>
References: <20210302100406.22059-1-rppt@kernel.org>
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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 | 19 ++++++++++---------
 1 file changed, 10 insertions(+), 9 deletions(-)

diff --git a/arch/x86/kernel/setup.c b/arch/x86/kernel/setup.c
index 3e3c6036b023..776fc9b3fafe 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();
 }
 
 /*
-- 
2.28.0