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authorArd Biesheuvel <ardb@kernel.org>2023-12-08 12:32:22 +0100
committerWill Deacon <will@kernel.org>2023-12-12 14:31:55 +0000
commit2632e25217696712681dd1f3ecc0d71624ea3b23 (patch)
tree68c6f91648a915e55493358fbc1229d84566eff5 /arch/arm64/kernel/fpsimd.c
parentaefbab8e77eb16b56e18f24b85a09ebf4dc60e93 (diff)
arm64: fpsimd: Implement lazy restore for kernel mode FPSIMD
Now that kernel mode FPSIMD state is context switched along with other task state, we can enable the existing logic that keeps track of which task's FPSIMD state the CPU is holding in its registers. If it is the context of the task that we are switching to, we can elide the reload of the FPSIMD state from memory. Note that we also need to check whether the FPSIMD state on this CPU is the most recent: if a task gets migrated away and back again, the state in memory may be more recent than the state in the CPU. So add another CPU id field to task_struct to keep track of this. (We could reuse the existing CPU id field used for user mode context, but that might result in user state to be discarded unnecessarily, given that two distinct CPUs could be holding the most recent user mode state and the most recent kernel mode state) Signed-off-by: Ard Biesheuvel <ardb@kernel.org> Reviewed-by: Mark Brown <broonie@kernel.org> Acked-by: Mark Rutland <mark.rutland@arm.com> Link: https://lore.kernel.org/r/20231208113218.3001940-9-ardb@google.com Signed-off-by: Will Deacon <will@kernel.org>
Diffstat (limited to 'arch/arm64/kernel/fpsimd.c')
-rw-r--r--arch/arm64/kernel/fpsimd.c18
1 files changed, 18 insertions, 0 deletions
diff --git a/arch/arm64/kernel/fpsimd.c b/arch/arm64/kernel/fpsimd.c
index e4595a8d731f..e714d0cd5d1e 100644
--- a/arch/arm64/kernel/fpsimd.c
+++ b/arch/arm64/kernel/fpsimd.c
@@ -1476,12 +1476,30 @@ void do_fpsimd_exc(unsigned long esr, struct pt_regs *regs)
static void fpsimd_load_kernel_state(struct task_struct *task)
{
+ struct cpu_fp_state *last = this_cpu_ptr(&fpsimd_last_state);
+
+ /*
+ * Elide the load if this CPU holds the most recent kernel mode
+ * FPSIMD context of the current task.
+ */
+ if (last->st == &task->thread.kernel_fpsimd_state &&
+ task->thread.kernel_fpsimd_cpu == smp_processor_id())
+ return;
+
fpsimd_load_state(&task->thread.kernel_fpsimd_state);
}
static void fpsimd_save_kernel_state(struct task_struct *task)
{
+ struct cpu_fp_state cpu_fp_state = {
+ .st = &task->thread.kernel_fpsimd_state,
+ .to_save = FP_STATE_FPSIMD,
+ };
+
fpsimd_save_state(&task->thread.kernel_fpsimd_state);
+ fpsimd_bind_state_to_cpu(&cpu_fp_state);
+
+ task->thread.kernel_fpsimd_cpu = smp_processor_id();
}
void fpsimd_thread_switch(struct task_struct *next)