path: root/arch
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authorJoerg Roedel <joerg.roedel@amd.com>2010-08-16 14:38:33 +0200
committerH. Peter Anvin <hpa@zytor.com>2010-08-18 09:17:20 -0700
commitfd89a137924e0710078c3ae855e7cec1c43cb845 (patch)
tree901f2048e637d3369ea4f0431dd618081ebeef93 /arch
parent07a7795ca2e6e66d00b184efb46bd0e23d90d3fe (diff)
x86-32: Separate 1:1 pagetables from swapper_pg_dir
This patch fixes machine crashes which occur when heavily exercising the CPU hotplug codepaths on a 32-bit kernel. These crashes are caused by AMD Erratum 383 and result in a fatal machine check exception. Here's the scenario: 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). By adding those low, large page (2M) mappings (PAE kernel), we create the necessary conditions for Erratum 383 to occur. 3. Other CPUs which do not participate in the off- and onlining game may use swapper_pg_dir while the low mappings are present (when leave_mm is called). For all steps below, the CPU referred to is a CPU that is using swapper_pg_dir, and not the CPU which is being onlined. 4. The presence of the low mappings in swapper_pg_dir can result in TLB entries for addresses below __PAGE_OFFSET to be established speculatively. These TLB entries are marked global and large. 5. When the CPU with such TLB entry switches to another page table, this TLB entry remains because it is global. 6. The process then generates an access to an address covered by the above TLB entry but there is a permission mismatch - the TLB entry covers a large global page not accessible to userspace. 7. Due to this permission mismatch a new 4kb, user TLB entry gets established. Further, Erratum 383 provides for a small window of time where both TLB entries are present. This results in an uncorrectable machine check exception signalling a TLB multimatch which panics the machine. 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 and with performance implications 2. Do not use swapper_pg_dir to boot secondary CPUs like 64-bit does. 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. -v2: switch to swapper_pg_dir right after entering start_secondary() so that we are able to access percpu data which might not be mapped in the trampoline page table. Signed-off-by: Joerg Roedel <joerg.roedel@amd.com> LKML-Reference: <20100816123833.GB28147@aftab> Signed-off-by: Borislav Petkov <borislav.petkov@amd.com> Signed-off-by: H. Peter Anvin <hpa@zytor.com>
Diffstat (limited to 'arch')
6 files changed, 44 insertions, 20 deletions
diff --git a/arch/x86/include/asm/pgtable_32.h b/arch/x86/include/asm/pgtable_32.h
index 2984a25ff38..f686f49e8b7 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 cb507bb05d7..8f78fdf3f17 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);
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 ff4c453e13f..fa8c1b8e09f 100644
--- a/arch/x86/kernel/head_32.S
+++ b/arch/x86/kernel/head_32.S
@@ -334,7 +334,7 @@ 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
@@ -614,6 +614,8 @@ ignore_int:
.align 4
.long i386_start_kernel
+ .long pa(swapper_pg_dir)
* BSS section
@@ -629,6 +631,10 @@ ENTRY(swapper_pg_dir)
.fill 1024,4,0
+ .fill 1024,4,0
.fill 4096,1,0
diff --git a/arch/x86/kernel/setup.c b/arch/x86/kernel/setup.c
index b008e788320..c3a4fbb2b99 100644
--- a/arch/x86/kernel/setup.c
+++ b/arch/x86/kernel/setup.c
@@ -1014,6 +1014,8 @@ void __init setup_arch(char **cmdline_p)
+ setup_trampoline_page_table();
#ifdef CONFIG_X86_64
diff --git a/arch/x86/kernel/smpboot.c b/arch/x86/kernel/smpboot.c
index a5e928b0cb5..abf4a86ffc5 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;
/* State of each CPU */
@@ -281,6 +280,18 @@ notrace static void __cpuinit start_secondary(void *unused)
* fragile that we want to limit the things done here to the
* most necessary things.
+#ifdef CONFIG_X86_32
+ /*
+ * Switch away from the trampoline page-table
+ *
+ * Do this before cpu_init() because it needs to access per-cpu
+ * data which may not be mapped in the trampoline page-table.
+ */
+ load_cr3(swapper_pg_dir);
+ __flush_tlb_all();
@@ -299,12 +310,6 @@ notrace static void __cpuinit start_secondary(void *unused)
-#ifdef CONFIG_X86_32
- while (low_mappings)
- cpu_relax();
- __flush_tlb_all();
/* This must be done before setting cpu_online_mask */
@@ -750,6 +755,7 @@ do_rest:
#ifdef CONFIG_X86_32
/* Stack for startup_32 can be just as for start_secondary onwards */
+ initial_page_table = __pa(&trampoline_pg_dir);
clear_tsk_thread_flag(c_idle.idle, TIF_FORK);
initial_gs = per_cpu_offset(cpu);
@@ -897,20 +903,8 @@ 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;
- err = do_boot_cpu(apicid, cpu);
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 c652ef62742..a874495b367 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,
+ /* Initialize low mappings */
+ clone_pgd_range(trampoline_pg_dir,
+ swapper_pg_dir + KERNEL_PGD_BOUNDARY,
+ min_t(unsigned long, KERNEL_PGD_PTRS,