[PATCH v2 5/7] arm64/efi: Use a semaphore to protect the EFI stack and FP/SIMD state
From: Ard Biesheuvel <hidden>
Date: 2025-09-05 13:30:54
Also in:
linux-efi, lkml
Subsystem:
arm64 port (aarch64 architecture), extensible firmware interface (efi), the rest · Maintainers:
Catalin Marinas, Will Deacon, Ard Biesheuvel, Linus Torvalds
From: Ard Biesheuvel <ardb@kernel.org> Replace the spinlock in the arm64 glue code with a semaphore, so that the CPU can preempted while running the EFI runtime service. Signed-off-by: Ard Biesheuvel <ardb@kernel.org> --- arch/arm64/kernel/efi.c | 13 ++++++++++--- 1 file changed, 10 insertions(+), 3 deletions(-)
diff --git a/arch/arm64/kernel/efi.c b/arch/arm64/kernel/efi.c
index 9b03f3d77a25..8b999c07c7d1 100644
--- a/arch/arm64/kernel/efi.c
+++ b/arch/arm64/kernel/efi.c@@ -165,12 +165,19 @@ asmlinkage efi_status_t efi_handle_corrupted_x18(efi_status_t s, const char *f) return s; } -static DEFINE_RAW_SPINLOCK(efi_rt_lock); +static DEFINE_SEMAPHORE(efi_rt_lock, 1); bool arch_efi_call_virt_setup(void) { + /* + * This might be called from a non-sleepable context so try to take the + * lock but don't block on it. This should never occur in practice, as + * all EFI runtime calls are serialized under the efi_runtime_lock. + */ + if (WARN_ON(down_trylock(&efi_rt_lock))) + return false; + efi_virtmap_load(); - raw_spin_lock(&efi_rt_lock); __efi_fpsimd_begin(); return true; }
@@ -178,8 +185,8 @@ bool arch_efi_call_virt_setup(void) void arch_efi_call_virt_teardown(void) { __efi_fpsimd_end(); - raw_spin_unlock(&efi_rt_lock); efi_virtmap_unload(); + up(&efi_rt_lock); } asmlinkage u64 *efi_rt_stack_top __ro_after_init;
--
2.51.0.355.g5224444f11-goog