Erratum 383 fix for 32 bit x86 kernels

Joerg Roedel
2010-09-24T12:08:04Z

Hi Greg,

here is a patch which I want to ask you to include into the current
-stable kernels. This patch fixes the occurence of AMD Erratum 383 on
32 bit x86 kernels when using CPU hotplug. This patch is a combined
patch created by cherry-picking (and fixing a small compile error)
upstream commits:

fd89a137924e0710078c3ae855e7cec1c43cb845
b7d460897739e02f186425b7276e3fdb1595cea7

The second commit fixes a problem in the first one. The patch I attach
here is against 2.6.32.22 but should also apply against 2.6.35 (At least
cherry-picking from 2.6.36-rc gave no conflicts).
Please consider to include this patch into the -stable kernel series.

Regards,

Joerg

>From d12a669119908f1c24a3b5037445c124c312eea5 Mon Sep 17 00:00:00 2001
From: Joerg Roedel <joerg.roedel@amd.com>
Date: Thu, 22 Jul 2010 11:32:00 +0200
Subject: [PATCH] x86-32: Fix crashes with CPU hotplug on AMD machines

This patch fixes machine crashes which occured when heavily
testing cpu hotplug code on a 32 bit kernel. The kernel
crashed because these tests triggered AMD erratum 383 which
resulted in a machine check exception.
The erratum triggered in the test cases because of the
following steps:

1. On 32 bit the swapper_pg_dir page table is used
as the initial page table for booting a secondary
cpu.

2. To make this work swapper_pg_dir needs a direct
mapping of physical memory in it (the low
mappings)

3. Other cpus may use swapper_pg_dir while the low
mappings are present (when leave_mm is called).

4. This can result in TLB entries for addresses
below __PAGE_OFFSET to be established due to
speculative TLB loads. These TLB entries are
marked global and possibly large.

5. When the CPU which has this entry loaded switches
to another page table this global TLB entry is not
flushed.

6. The process accesses an address covered by this
TLB entry but there is a permission mismatch
(present TLB entry covers a large global page not
accessible for userspace).

7. Due to the permission mismatch the hardware
walks the new page table and establishes a new
4kb TLB entry. Due to AMD erratum 383 there might
be a small window of time now where both TLB
entries are present.

8. After the page walk the hardware does a new TLB
lookup which may result in two matches. This
results in a machine check exception which
signals a TLB multimatch error. The machine
crashes.

There are two ways to fix this issue:

1. Always do a global TLB flush when a new cr3 is
loaded and the old page table was swapper_pg_dir.
I consider this a hack hard to understand.

2. Do not use swapper_pg_dir to boot secondary cpus.

This patch implements solution 2. It introduces a
trampoline_pg_dir which has the same layout as
swapper_pg_dir with low_mappings. This page table is used as
the initial page table of the booting cpu. Later in the
bringup process it switches to swapper_pg_dir and does a
global tlb flush. This fixes the crashes in our test cases.

Signed-off-by: Joerg Roedel <joerg.roedel@amd.com>
---
arch/x86/include/asm/pgtable_32.h | 1 +
arch/x86/include/asm/trampoline.h | 3 +++
arch/x86/kernel/head_32.S | 8 +++++++-
arch/x86/kernel/setup.c | 2 ++
arch/x86/kernel/smpboot.c | 21 ++++++---------------
arch/x86/kernel/trampoline.c | 18 ++++++++++++++++++
6 files changed, 37 insertions(+), 16 deletions(-)

diff --git a/arch/x86/include/asm/pgtable_32.h b/arch/x86/include/asm/pgtable_32.h
index 2984a25..f686f49 100644
--- a/arch/x86/include/asm/pgtable_32.h
+++ b/arch/x86/include/asm/pgtable_32.h
@@ -26,6 +26,7 @@ struct mm_struct;
struct vm_area_struct;

extern pgd_t swapper_pg_dir[1024];
+extern pgd_t trampoline_pg_dir[1024];

static inline void pgtable_cache_init(void) { }
static inline void check_pgt_cache(void) { }
diff --git a/arch/x86/include/asm/trampoline.h b/arch/x86/include/asm/trampoline.h
index cb507bb..8f78fdf 100644
--- a/arch/x86/include/asm/trampoline.h
+++ b/arch/x86/include/asm/trampoline.h
@@ -13,14 +13,17 @@ extern unsigned char *trampoline_base;

extern unsigned long init_rsp;
extern unsigned long initial_code;
+extern unsigned long initial_page_table;
extern unsigned long initial_gs;

#define TRAMPOLINE_SIZE roundup(trampoline_end - trampoline_data, PAGE_SIZE)

extern unsigned long setup_trampoline(void);
+extern void __init setup_trampoline_page_table(void);
extern void __init reserve_trampoline_memory(void);
#else
static inline void reserve_trampoline_memory(void) {};
+extern void __init setup_trampoline_page_table(void) {};
#endif /* CONFIG_X86_TRAMPOLINE */

#endif /* __ASSEMBLY__ */
diff --git a/arch/x86/kernel/head_32.S b/arch/x86/kernel/head_32.S
index 37c3d4b..75e3981 100644
--- a/arch/x86/kernel/head_32.S
+++ b/arch/x86/kernel/head_32.S
@@ -328,7 +328,7 @@ ENTRY(startup_32_smp)
/*
* Enable paging
*/
- movl $pa(swapper_pg_dir),%eax
+ movl pa(initial_page_table), %eax
movl %eax,%cr3 /* set the page table pointer.. */
movl %cr0,%eax
orl $X86_CR0_PG,%eax
@@ -608,6 +608,8 @@ ignore_int:
.align 4
ENTRY(initial_code)
.long i386_start_kernel
+ENTRY(initial_page_table)
+ .long pa(swapper_pg_dir)

/*
* BSS section
@@ -623,6 +625,10 @@ ENTRY(swapper_pg_dir)
#endif
swapper_pg_fixmap:
.fill 1024,4,0
+#ifdef CONFIG_X86_TRAMPOLINE
+ENTRY(trampoline_pg_dir)
+ .fill 1024,4,0
+#endif
ENTRY(empty_zero_page)
.fill 4096,1,0

diff --git a/arch/x86/kernel/setup.c b/arch/x86/kernel/setup.c
index b4ae4ac..6600cfd 100644
--- a/arch/x86/kernel/setup.c
+++ b/arch/x86/kernel/setup.c
@@ -1008,6 +1008,8 @@ void __init setup_arch(char **cmdline_p)
paging_init();
x86_init.paging.pagetable_setup_done(swapper_pg_dir);

+ setup_trampoline_page_table();
+
tboot_probe();

#ifdef CONFIG_X86_64
diff --git a/arch/x86/kernel/smpboot.c b/arch/x86/kernel/smpboot.c
index c4f33b2..7b05eb1 100644
--- a/arch/x86/kernel/smpboot.c
+++ b/arch/x86/kernel/smpboot.c
@@ -73,7 +73,6 @@

#ifdef CONFIG_X86_32
u8 apicid_2_node[MAX_APICID];
-static int low_mappings;
#endif

/* State of each CPU */
@@ -300,8 +299,8 @@ notrace static void __cpuinit start_secondary(void *unused)
}

#ifdef CONFIG_X86_32
- while (low_mappings)
- cpu_relax();
+ /* switch away from the trampoline page-table */
+ load_cr3(swapper_pg_dir);
__flush_tlb_all();
#endif

@@ -765,6 +764,10 @@ do_rest:
initial_code = (unsigned long)start_secondary;
stack_start.sp = (void *) c_idle.idle->thread.sp;

+#ifdef CONFIG_X86_32
+ initial_page_table = __pa(&trampoline_pg_dir);
+#endif
+
/* start_ip had better be page-aligned! */
start_ip = setup_trampoline();

@@ -894,20 +897,8 @@ int __cpuinit native_cpu_up(unsigned int cpu)

per_cpu(cpu_state, cpu) = CPU_UP_PREPARE;

-#ifdef CONFIG_X86_32
- /* init low mem mapping */
- clone_pgd_range(swapper_pg_dir, swapper_pg_dir + KERNEL_PGD_BOUNDARY,
- min_t(unsigned long, KERNEL_PGD_PTRS, KERNEL_PGD_BOUNDARY));
- flush_tlb_all();
- low_mappings = 1;
-
err = do_boot_cpu(apicid, cpu);

- zap_low_mappings(false);
- low_mappings = 0;
-#else
- err = do_boot_cpu(apicid, cpu);
-#endif
if (err) {
pr_debug("do_boot_cpu failed %d\n", err);
return -EIO;
diff --git a/arch/x86/kernel/trampoline.c b/arch/x86/kernel/trampoline.c
index c652ef6..a874495 100644
--- a/arch/x86/kernel/trampoline.c
+++ b/arch/x86/kernel/trampoline.c
@@ -1,6 +1,7 @@
#include <linux/io.h>

#include <asm/trampoline.h>
+#include <asm/pgtable.h>
#include <asm/e820.h>

#if defined(CONFIG_X86_64) && defined(CONFIG_ACPI_SLEEP)
@@ -37,3 +38,20 @@ unsigned long __trampinit setup_trampoline(void)
memcpy(trampoline_base, trampoline_data, TRAMPOLINE_SIZE);
return virt_to_phys(trampoline_base);
}
+
+void __init setup_trampoline_page_table(void)
+{
+#ifdef CONFIG_X86_32
+ /* Copy kernel address range */
+ clone_pgd_range(trampoline_pg_dir + KERNEL_PGD_BOUNDARY,
+ swapper_pg_dir + KERNEL_PGD_BOUNDARY,
+ min_t(unsigned long, KERNEL_PGD_PTRS,
+ KERNEL_PGD_BOUNDARY));
+
+ /* Initialize low mappings */
+ clone_pgd_range(trampoline_pg_dir,
+ swapper_pg_dir + KERNEL_PGD_BOUNDARY,
+ min_t(unsigned long, KERNEL_PGD_PTRS,
+ KERNEL_PGD_BOUNDARY));
+#endif
+}
--
1.7.0.4

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