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-rw-r--r--0005-x86-setup-always-reserve-the-first-1M-of-RAM.patch170
1 files changed, 170 insertions, 0 deletions
diff --git a/0005-x86-setup-always-reserve-the-first-1M-of-RAM.patch b/0005-x86-setup-always-reserve-the-first-1M-of-RAM.patch
new file mode 100644
index 00000000000..169ba22ae2d
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+++ b/0005-x86-setup-always-reserve-the-first-1M-of-RAM.patch
@@ -0,0 +1,170 @@
+From 3ffe8ae29143ee20e01b0bc4a63774182b59daf9 Mon Sep 17 00:00:00 2001
+From: Mike Rapoport <rppt@linux.ibm.com>
+Date: Tue, 1 Jun 2021 10:53:52 +0300
+Subject: [PATCH 5/8] x86/setup: always reserve the first 1M of RAM
+
+There are BIOSes that are known to corrupt the memory under 1M, or more
+precisely under 640K because the memory above 640K is anyway reserved for
+the EGA/VGA frame buffer and BIOS.
+
+To prevent usage of the memory that will be potentially clobbered by the
+kernel, the beginning of the memory is always reserved. The exact size of
+the reserved area is determined by CONFIG_X86_RESERVE_LOW build time and
+reservelow command line option. The reserved range may be from 4K to 640K
+with the default of 64K. There are also configurations that reserve the
+entire 1M range, like machines with SandyBridge graphic devices or systems
+that enable crash kernel.
+
+In addition to the potentially clobbered memory, EBDA of unknown size may
+be as low as 128K and the memory above that EBDA start is also reserved
+early.
+
+It would have been possible to reserve the entire range under 1M unless for
+the real mode trampoline that must reside in that area.
+
+To accommodate placement of the real mode trampoline and keep the memory
+safe from being clobbered by BIOS reserve the first 64K of RAM before
+memory allocations are possible and then, after the real mode trampoline is
+allocated, reserve the entire range from 0 to 1M.
+
+Update trim_snb_memory() and reserve_real_mode() to avoid redundant
+reservations of the same memory range.
+
+Also make sure the memory under 1M is not getting freed by
+efi_free_boot_services().
+
+Fixes: a799c2bd29d1 ("x86/setup: Consolidate early memory reservations")
+Signed-off-by: Mike Rapoport <rppt@linux.ibm.com>
+---
+ arch/x86/kernel/setup.c | 35 ++++++++++++++++++++--------------
+ arch/x86/platform/efi/quirks.c | 12 ++++++++++++
+ arch/x86/realmode/init.c | 14 ++++++++------
+ 3 files changed, 41 insertions(+), 20 deletions(-)
+
+diff --git a/arch/x86/kernel/setup.c b/arch/x86/kernel/setup.c
+index 7d466f51be1f..d7cfb927864f 100644
+--- a/arch/x86/kernel/setup.c
++++ b/arch/x86/kernel/setup.c
+@@ -638,11 +638,11 @@ static void __init trim_snb_memory(void)
+ * them from accessing certain memory ranges, namely anything below
+ * 1M and in the pages listed in bad_pages[] above.
+ *
+- * To avoid these pages being ever accessed by SNB gfx devices
+- * reserve all memory below the 1 MB mark and bad_pages that have
+- * not already been reserved at boot time.
++ * To avoid these pages being ever accessed by SNB gfx devices reserve
++ * bad_pages that have not already been reserved at boot time.
++ * All memory below the 1 MB mark is anyway reserved later during
++ * setup_arch(), so there is no need to reserve it here.
+ */
+- memblock_reserve(0, 1<<20);
+
+ for (i = 0; i < ARRAY_SIZE(bad_pages); i++) {
+ if (memblock_reserve(bad_pages[i], PAGE_SIZE))
+@@ -734,14 +734,14 @@ static void __init early_reserve_memory(void)
+ * 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.
++ * Reserve the first 64K of memory since some BIOSes are known to
++ * corrupt low memory. After the real mode trampoline is allocated the
++ * rest of the memory below 640k is reserved.
+ *
+ * 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, ALIGN(reserve_low, PAGE_SIZE));
++ memblock_reserve(0, SZ_64K);
+
+ early_reserve_initrd();
+
+@@ -752,6 +752,7 @@ static void __init early_reserve_memory(void)
+
+ reserve_ibft_region();
+ reserve_bios_regions();
++ trim_snb_memory();
+ }
+
+ /*
+@@ -1083,14 +1084,20 @@ void __init setup_arch(char **cmdline_p)
+ (max_pfn_mapped<<PAGE_SHIFT) - 1);
+ #endif
+
+- reserve_real_mode();
+-
+ /*
+- * Reserving memory causing GPU hangs on Sandy Bridge integrated
+- * graphics devices should be done after we allocated memory under
+- * 1M for the real mode trampoline.
++ * Find free memory for the real mode trampoline and place it
++ * there.
++ * If there is not enough free memory under 1M, on EFI-enabled
++ * systems there will be additional attempt to reclaim the memory
++ * for the real mode trampoline at efi_free_boot_services().
++ *
++ * Unconditionally reserve the entire first 1M of RAM because
++ * BIOSes are know to corrupt low memory and several
++ * hundred kilobytes are not worth complex detection what memory gets
++ * clobbered. Moreover, on machines with SandyBridge graphics or in
++ * setups that use crashkernel the entire 1M is anyway reserved.
+ */
+- trim_snb_memory();
++ reserve_real_mode();
+
+ init_mem_mapping();
+
+diff --git a/arch/x86/platform/efi/quirks.c b/arch/x86/platform/efi/quirks.c
+index 67d93a243c35..27561b56a821 100644
+--- a/arch/x86/platform/efi/quirks.c
++++ b/arch/x86/platform/efi/quirks.c
+@@ -450,6 +450,18 @@ void __init efi_free_boot_services(void)
+ size -= rm_size;
+ }
+
++ /*
++ * Don't free memory under 1M for two reasons:
++ * - BIOS might clobber it
++ * - Crash kernel needs it to be reserved
++ */
++ if (start + size < SZ_1M)
++ continue;
++ if (start < SZ_1M) {
++ size -= (SZ_1M - start);
++ start = SZ_1M;
++ }
++
+ memblock_free_late(start, size);
+ }
+
+diff --git a/arch/x86/realmode/init.c b/arch/x86/realmode/init.c
+index 22fda7d99159..ea42630d4e2e 100644
+--- a/arch/x86/realmode/init.c
++++ b/arch/x86/realmode/init.c
+@@ -29,14 +29,16 @@ void __init reserve_real_mode(void)
+
+ /* Has to be under 1M so we can execute real-mode AP code. */
+ mem = memblock_find_in_range(0, 1<<20, size, PAGE_SIZE);
+- if (!mem) {
++ if (!mem)
+ pr_info("No sub-1M memory is available for the trampoline\n");
+- return;
+- }
++ else
++ set_real_mode_mem(mem);
+
+- memblock_reserve(mem, size);
+- set_real_mode_mem(mem);
+- crash_reserve_low_1M();
++ /*
++ * Unconditionally reserve the entire fisrt 1M, see comment in
++ * setup_arch()
++ */
++ memblock_reserve(0, SZ_1M);
+ }
+
+ static void sme_sev_setup_real_mode(struct trampoline_header *th)
+--
+2.32.0
+