From: Tao Liu ltao@redhat.com
[ Upstream commit 5760929f6545c651682de3c2c6c6786816b17bb1 ]
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 Signed-off-by: Sasha Levin sashal@kernel.org --- 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 cc0f7f70b17ba..9c9ac606893e9 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;