From: Tao Liu <ltao@redhat.com>
A kexec kernel boot failure is sometimes observed on AMD CPUs due to
an unmapped EFI config table array. This can be seen when "nogbpages"
is on the kernel command line, and has been observed as a full BIOS
reboot rather than a successful kexec.
This was also the cause of reported regressions attributed to Commit
7143c5f4cf20 ("x86/mm/ident_map: Use gbpages only where full GB page
should be mapped.") which was subsequently reverted.
To avoid this page fault, explicitly include the EFI config table
array in the kexec identity map.
Further explanation:
The following 2 commits caused the EFI config table array to be
accessed when enabling sev at kernel startup.
commit ec1c66af3a30 ("x86/compressed/64: Detect/setup SEV/SME features
earlier during boot")
commit c01fce9cef84 ("x86/compressed: Add SEV-SNP feature
detection/setup")
This is in the code that examines whether SEV should be enabled or
not, so it can even affect systems that are not SEV capable.
This may result in a page fault if the EFI config table array's
address is unmapped. Since the page fault occurs before the new kernel
establishes its own identity map and page fault routines, it is
unrecoverable and kexec fails.
Most often, this problem is not seen because the EFI config table
array gets included in the map by the luck of being placed at a memory
address close enough to other memory areas that *are* included in the
map created by kexec.
Both the "nogbpages" command line option and the "use gpbages only
where full GB page should be mapped" patch greatly reduce the chance
of being included in the map by luck, which is why the problem
appears.
Signed-off-by: Tao Liu <ltao@redhat.com>
Signed-off-by: Steve Wahl <steve.wahl@hpe.com>
Tested-by: Pavin Joseph <me@pavinjoseph.com>
Tested-by: Sarah Brofeldt <srhb@dbc.dk>
Tested-by: Eric Hagberg <ehagberg@gmail.com>
---
Version 3: Do not rename map_efi_systab to map_efi_tables, and don't add
'config table' to the comments, per Ard Biesheuvel request.
arch/x86/kernel/machine_kexec_64.c | 27 +++++++++++++++++++++++++++
1 file changed, 27 insertions(+)
diff --git a/arch/x86/kernel/machine_kexec_64.c b/arch/x86/kernel/machine_kexec_64.c
index cc0f7f70b17b..9c9ac606893e 100644
--- a/arch/x86/kernel/machine_kexec_64.c
+++ b/arch/x86/kernel/machine_kexec_64.c
@@ -28,6 +28,7 @@
#include <asm/setup.h>
#include <asm/set_memory.h>
#include <asm/cpu.h>
+#include <asm/efi.h>
#ifdef CONFIG_ACPI
/*
@@ -87,6 +88,8 @@ map_efi_systab(struct x86_mapping_info *info, pgd_t *level4p)
{
#ifdef CONFIG_EFI
unsigned long mstart, mend;
+ void *kaddr;
+ int ret;
if (!efi_enabled(EFI_BOOT))
return 0;
@@ -102,6 +105,30 @@ map_efi_systab(struct x86_mapping_info *info, pgd_t *level4p)
if (!mstart)
return 0;
+ ret = kernel_ident_mapping_init(info, level4p, mstart, mend);
+ if (ret)
+ return ret;
+
+ kaddr = memremap(mstart, mend - mstart, MEMREMAP_WB);
+ if (!kaddr) {
+ pr_err("Could not map UEFI system table\n");
+ return -ENOMEM;
+ }
+
+ mstart = efi_config_table;
+
+ if (efi_enabled(EFI_64BIT)) {
+ efi_system_table_64_t *stbl = (efi_system_table_64_t *)kaddr;
+
+ mend = mstart + sizeof(efi_config_table_64_t) * stbl->nr_tables;
+ } else {
+ efi_system_table_32_t *stbl = (efi_system_table_32_t *)kaddr;
+
+ mend = mstart + sizeof(efi_config_table_32_t) * stbl->nr_tables;
+ }
+
+ memunmap(kaddr);
+
return kernel_ident_mapping_init(info, level4p, mstart, mend);
#endif
return 0;
--
2.26.2On Wed, 17 Jul 2024 at 14:32, Steve Wahl <steve.wahl@hpe.com> wrote:
>
> From: Tao Liu <ltao@redhat.com>
>
> A kexec kernel boot failure is sometimes observed on AMD CPUs due to
> an unmapped EFI config table array. This can be seen when "nogbpages"
> is on the kernel command line, and has been observed as a full BIOS
> reboot rather than a successful kexec.
>
> This was also the cause of reported regressions attributed to Commit
> 7143c5f4cf20 ("x86/mm/ident_map: Use gbpages only where full GB page
> should be mapped.") which was subsequently reverted.
>
> To avoid this page fault, explicitly include the EFI config table
> array in the kexec identity map.
>
> Further explanation:
>
> The following 2 commits caused the EFI config table array to be
> accessed when enabling sev at kernel startup.
>
> commit ec1c66af3a30 ("x86/compressed/64: Detect/setup SEV/SME features
> earlier during boot")
> commit c01fce9cef84 ("x86/compressed: Add SEV-SNP feature
> detection/setup")
>
> This is in the code that examines whether SEV should be enabled or
> not, so it can even affect systems that are not SEV capable.
>
> This may result in a page fault if the EFI config table array's
> address is unmapped. Since the page fault occurs before the new kernel
> establishes its own identity map and page fault routines, it is
> unrecoverable and kexec fails.
>
> Most often, this problem is not seen because the EFI config table
> array gets included in the map by the luck of being placed at a memory
> address close enough to other memory areas that *are* included in the
> map created by kexec.
>
> Both the "nogbpages" command line option and the "use gpbages only
> where full GB page should be mapped" patch greatly reduce the chance
> of being included in the map by luck, which is why the problem
> appears.
>
> Signed-off-by: Tao Liu <ltao@redhat.com>
> Signed-off-by: Steve Wahl <steve.wahl@hpe.com>
> Tested-by: Pavin Joseph <me@pavinjoseph.com>
> Tested-by: Sarah Brofeldt <srhb@dbc.dk>
> Tested-by: Eric Hagberg <ehagberg@gmail.com>
> ---
>
> Version 3: Do not rename map_efi_systab to map_efi_tables, and don't add
> 'config table' to the comments, per Ard Biesheuvel request.
>
> arch/x86/kernel/machine_kexec_64.c | 27 +++++++++++++++++++++++++++
> 1 file changed, 27 insertions(+)
>
Reviewed-by: Ard Biesheuvel <ardb@kernel.org>
The following commit has been merged into the x86/mm branch of tip:
Commit-ID: 5760929f6545c651682de3c2c6c6786816b17bb1
Gitweb: https://git.kernel.org/tip/5760929f6545c651682de3c2c6c6786816b17bb1
Author: Tao Liu <ltao@redhat.com>
AuthorDate: Wed, 17 Jul 2024 16:31:20 -05:00
Committer: Thomas Gleixner <tglx@linutronix.de>
CommitterDate: Mon, 05 Aug 2024 16:09:31 +02:00
x86/kexec: Add EFI config table identity mapping for kexec kernel
A kexec kernel boot failure is sometimes observed on AMD CPUs due to an
unmapped EFI config table array. This can be seen when "nogbpages" is on
the kernel command line, and has been observed as a full BIOS reboot rather
than a successful kexec.
This was also the cause of reported regressions attributed to Commit
7143c5f4cf20 ("x86/mm/ident_map: Use gbpages only where full GB page should
be mapped.") which was subsequently reverted.
To avoid this page fault, explicitly include the EFI config table array in
the kexec identity map.
Further explanation:
The following 2 commits caused the EFI config table array to be
accessed when enabling sev at kernel startup.
commit ec1c66af3a30 ("x86/compressed/64: Detect/setup SEV/SME features
earlier during boot")
commit c01fce9cef84 ("x86/compressed: Add SEV-SNP feature
detection/setup")
This is in the code that examines whether SEV should be enabled or not, so
it can even affect systems that are not SEV capable.
This may result in a page fault if the EFI config table array's address is
unmapped. Since the page fault occurs before the new kernel establishes its
own identity map and page fault routines, it is unrecoverable and kexec
fails.
Most often, this problem is not seen because the EFI config table array
gets included in the map by the luck of being placed at a memory address
close enough to other memory areas that *are* included in the map created
by kexec.
Both the "nogbpages" command line option and the "use gpbages only where
full GB page should be mapped" change greatly reduce the chance of being
included in the map by luck, which is why the problem appears.
Signed-off-by: Tao Liu <ltao@redhat.com>
Signed-off-by: Steve Wahl <steve.wahl@hpe.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Tested-by: Pavin Joseph <me@pavinjoseph.com>
Tested-by: Sarah Brofeldt <srhb@dbc.dk>
Tested-by: Eric Hagberg <ehagberg@gmail.com>
Reviewed-by: Ard Biesheuvel <ardb@kernel.org>
Link: https://lore.kernel.org/all/20240717213121.3064030-2-steve.wahl@hpe.com
---
arch/x86/kernel/machine_kexec_64.c | 27 +++++++++++++++++++++++++++
1 file changed, 27 insertions(+)
diff --git a/arch/x86/kernel/machine_kexec_64.c b/arch/x86/kernel/machine_kexec_64.c
index cc0f7f7..9c9ac60 100644
--- a/arch/x86/kernel/machine_kexec_64.c
+++ b/arch/x86/kernel/machine_kexec_64.c
@@ -28,6 +28,7 @@
#include <asm/setup.h>
#include <asm/set_memory.h>
#include <asm/cpu.h>
+#include <asm/efi.h>
#ifdef CONFIG_ACPI
/*
@@ -87,6 +88,8 @@ map_efi_systab(struct x86_mapping_info *info, pgd_t *level4p)
{
#ifdef CONFIG_EFI
unsigned long mstart, mend;
+ void *kaddr;
+ int ret;
if (!efi_enabled(EFI_BOOT))
return 0;
@@ -102,6 +105,30 @@ map_efi_systab(struct x86_mapping_info *info, pgd_t *level4p)
if (!mstart)
return 0;
+ ret = kernel_ident_mapping_init(info, level4p, mstart, mend);
+ if (ret)
+ return ret;
+
+ kaddr = memremap(mstart, mend - mstart, MEMREMAP_WB);
+ if (!kaddr) {
+ pr_err("Could not map UEFI system table\n");
+ return -ENOMEM;
+ }
+
+ mstart = efi_config_table;
+
+ if (efi_enabled(EFI_64BIT)) {
+ efi_system_table_64_t *stbl = (efi_system_table_64_t *)kaddr;
+
+ mend = mstart + sizeof(efi_config_table_64_t) * stbl->nr_tables;
+ } else {
+ efi_system_table_32_t *stbl = (efi_system_table_32_t *)kaddr;
+
+ mend = mstart + sizeof(efi_config_table_32_t) * stbl->nr_tables;
+ }
+
+ memunmap(kaddr);
+
return kernel_ident_mapping_init(info, level4p, mstart, mend);
#endif
return 0;© 2016 - 2025 Red Hat, Inc.