arm64: fpsimd: Split cpu field out from struct fpsimd_state

In preparation for using a common representation of the FPSIMD
state for tasks and KVM vcpus, this patch separates out the "cpu"
field that is used to track the cpu on which the state was most
recently loaded.

This will allow common code to operate on task and vcpu contexts
without requiring the cpu field to be stored at the same offset
from the FPSIMD register data in both cases.  This should avoid the
need for messing with the definition of those parts of struct
vcpu_arch that are exposed in the KVM user ABI.

The resulting change is also convenient for grouping and defining
the set of thread_struct fields that are supposed to be accessible
to copy_{to,from}_user(), which includes user_fpsimd_state but
should exclude the cpu field.  This patch does not amend the
usercopy whitelist to match: that will be addressed in a subsequent
patch.
Signed-off-by: Dave Martin <Dave.Martin@arm.com>
[will: inline fpsimd_flush_state for now]
Signed-off-by: Will Deacon <will.deacon@arm.com>

arch/arm64/include/asm/fpsimd.h

@@ -25,31 +25,6 @@
 #include <linux/init.h>
 #include <linux/stddef.h>
 
-/*
- * FP/SIMD storage area has:
- *  - FPSR and FPCR
- *  - 32 128-bit data registers
- *
- * Note that user_fpsimd forms a prefix of this structure, which is
- * relied upon in the ptrace FP/SIMD accessors.
- */
-struct fpsimd_state {
-	union {
-		struct user_fpsimd_state user_fpsimd;
-		struct {
-			__uint128_t vregs[32];
-			u32 fpsr;
-			u32 fpcr;
-			/*
-			 * For ptrace compatibility, pad to next 128-bit
-			 * boundary here if extending this struct.
-			 */
-		};
-	};
-	/* the id of the last cpu to have restored this state */
-	unsigned int cpu;
-};
-
 #if defined(__KERNEL__) && defined(CONFIG_COMPAT)
 /* Masks for extracting the FPSR and FPCR from the FPSCR */
 #define VFP_FPSCR_STAT_MASK	0xf800009f
@@ -63,8 +38,8 @@ struct fpsimd_state {
 
 struct task_struct;
 
-extern void fpsimd_save_state(struct fpsimd_state *state);
-extern void fpsimd_load_state(struct fpsimd_state *state);
+extern void fpsimd_save_state(struct user_fpsimd_state *state);
+extern void fpsimd_load_state(struct user_fpsimd_state *state);
 
 extern void fpsimd_thread_switch(struct task_struct *next);
 extern void fpsimd_flush_thread(void);

arch/arm64/include/asm/processor.h

@@ -38,7 +38,6 @@
 
 #include <asm/alternative.h>
 #include <asm/cpufeature.h>
-#include <asm/fpsimd.h>
 #include <asm/hw_breakpoint.h>
 #include <asm/lse.h>
 #include <asm/pgtable-hwdef.h>
@@ -108,7 +107,8 @@ struct thread_struct {
 #ifdef CONFIG_COMPAT
 	unsigned long		tp2_value;
 #endif
-	struct fpsimd_state	fpsimd_state;
+	struct user_fpsimd_state fpsimd_state;
+	unsigned int		fpsimd_cpu;
 	void			*sve_state;	/* SVE registers, if any */
 	unsigned int		sve_vl;		/* SVE vector length */
 	unsigned int		sve_vl_onexec;	/* SVE vl after next exec */

arch/arm64/kernel/fpsimd.c

@@ -66,7 +66,7 @@
  *     been loaded into its FPSIMD registers most recently, or whether it has
  *     been used to perform kernel mode NEON in the meantime.
  *
- * For (a), we add a 'cpu' field to struct fpsimd_state, which gets updated to
+ * For (a), we add a fpsimd_cpu field to thread_struct, which gets updated to
  * the id of the current CPU every time the state is loaded onto a CPU. For (b),
  * we add the per-cpu variable 'fpsimd_last_state' (below), which contains the
  * address of the userland FPSIMD state of the task that was loaded onto the CPU
@@ -75,7 +75,7 @@
  * With this in place, we no longer have to restore the next FPSIMD state right
  * when switching between tasks. Instead, we can defer this check to userland
  * resume, at which time we verify whether the CPU's fpsimd_last_state and the
- * task's fpsimd_state.cpu are still mutually in sync. If this is the case, we
+ * task's fpsimd_cpu are still mutually in sync. If this is the case, we
  * can omit the FPSIMD restore.
  *
  * As an optimization, we use the thread_info flag TIF_FOREIGN_FPSTATE to
@@ -92,14 +92,14 @@
  * flag with local_bh_disable() unless softirqs are already masked.
  *
  * For a certain task, the sequence may look something like this:
- * - the task gets scheduled in; if both the task's fpsimd_state.cpu field
+ * - the task gets scheduled in; if both the task's fpsimd_cpu field
  *   contains the id of the current CPU, and the CPU's fpsimd_last_state per-cpu
  *   variable points to the task's fpsimd_state, the TIF_FOREIGN_FPSTATE flag is
  *   cleared, otherwise it is set;
  *
  * - the task returns to userland; if TIF_FOREIGN_FPSTATE is set, the task's
  *   userland FPSIMD state is copied from memory to the registers, the task's
- *   fpsimd_state.cpu field is set to the id of the current CPU, the current
+ *   fpsimd_cpu field is set to the id of the current CPU, the current
  *   CPU's fpsimd_last_state pointer is set to this task's fpsimd_state and the
  *   TIF_FOREIGN_FPSTATE flag is cleared;
  *
@@ -117,7 +117,7 @@
  *   whatever is in the FPSIMD registers is not saved to memory, but discarded.
  */
 struct fpsimd_last_state_struct {
-	struct fpsimd_state *st;
+	struct user_fpsimd_state *st;
 	bool sve_in_use;
 };
 
@@ -418,7 +418,7 @@ static void fpsimd_to_sve(struct task_struct *task)
 {
 	unsigned int vq;
 	void *sst = task->thread.sve_state;
-	struct fpsimd_state const *fst = &task->thread.fpsimd_state;
+	struct user_fpsimd_state const *fst = &task->thread.fpsimd_state;
 	unsigned int i;
 
 	if (!system_supports_sve())
@@ -444,7 +444,7 @@ static void sve_to_fpsimd(struct task_struct *task)
 {
 	unsigned int vq;
 	void const *sst = task->thread.sve_state;
-	struct fpsimd_state *fst = &task->thread.fpsimd_state;
+	struct user_fpsimd_state *fst = &task->thread.fpsimd_state;
 	unsigned int i;
 
 	if (!system_supports_sve())
@@ -540,7 +540,7 @@ void sve_sync_from_fpsimd_zeropad(struct task_struct *task)
 {
 	unsigned int vq;
 	void *sst = task->thread.sve_state;
-	struct fpsimd_state const *fst = &task->thread.fpsimd_state;
+	struct user_fpsimd_state const *fst = &task->thread.fpsimd_state;
 	unsigned int i;
 
 	if (!test_tsk_thread_flag(task, TIF_SVE))
@@ -909,10 +909,9 @@ void fpsimd_thread_switch(struct task_struct *next)
 		 * the TIF_FOREIGN_FPSTATE flag so the state will be loaded
 		 * upon the next return to userland.
 		 */
-		struct fpsimd_state *st = &next->thread.fpsimd_state;
-
-		if (__this_cpu_read(fpsimd_last_state.st) == st
-		    && st->cpu == smp_processor_id())
+		if (__this_cpu_read(fpsimd_last_state.st) ==
+			&next->thread.fpsimd_state
+		    && next->thread.fpsimd_cpu == smp_processor_id())
 			clear_tsk_thread_flag(next, TIF_FOREIGN_FPSTATE);
 		else
 			set_tsk_thread_flag(next, TIF_FOREIGN_FPSTATE);
@@ -928,7 +927,8 @@ void fpsimd_flush_thread(void)
 
 	local_bh_disable();
 
-	memset(&current->thread.fpsimd_state, 0, sizeof(struct fpsimd_state));
+	memset(&current->thread.fpsimd_state, 0,
+	       sizeof(current->thread.fpsimd_state));
 	fpsimd_flush_task_state(current);
 
 	if (system_supports_sve()) {
@@ -1005,11 +1005,10 @@ static void fpsimd_bind_to_cpu(void)
 {
 	struct fpsimd_last_state_struct *last =
 		this_cpu_ptr(&fpsimd_last_state);
-	struct fpsimd_state *st = &current->thread.fpsimd_state;
 
-	last->st = st;
+	last->st = &current->thread.fpsimd_state;
 	last->sve_in_use = test_thread_flag(TIF_SVE);
-	st->cpu = smp_processor_id();
+	current->thread.fpsimd_cpu = smp_processor_id();
 }
 
 /*
@@ -1044,7 +1043,7 @@ void fpsimd_update_current_state(struct user_fpsimd_state const *state)
 
 	local_bh_disable();
 
-	current->thread.fpsimd_state.user_fpsimd = *state;
+	current->thread.fpsimd_state = *state;
 	if (system_supports_sve() && test_thread_flag(TIF_SVE))
 		fpsimd_to_sve(current);
 
@@ -1061,7 +1060,7 @@ void fpsimd_update_current_state(struct user_fpsimd_state const *state)
  */
 void fpsimd_flush_task_state(struct task_struct *t)
 {
-	t->thread.fpsimd_state.cpu = NR_CPUS;
+	t->thread.fpsimd_cpu = NR_CPUS;
 }
 
 static inline void fpsimd_flush_cpu_state(void)
@@ -1160,7 +1159,7 @@ EXPORT_SYMBOL(kernel_neon_end);
 
 #ifdef CONFIG_EFI
 
-static DEFINE_PER_CPU(struct fpsimd_state, efi_fpsimd_state);
+static DEFINE_PER_CPU(struct user_fpsimd_state, efi_fpsimd_state);
 static DEFINE_PER_CPU(bool, efi_fpsimd_state_used);
 static DEFINE_PER_CPU(bool, efi_sve_state_used);
 

arch/arm64/kernel/ptrace.c

@@ -629,7 +629,7 @@ static int __fpr_get(struct task_struct *target,
 
 	sve_sync_to_fpsimd(target);
 
-	uregs = &target->thread.fpsimd_state.user_fpsimd;
+	uregs = &target->thread.fpsimd_state;
 
 	return user_regset_copyout(&pos, &count, &kbuf, &ubuf, uregs,
 				   start_pos, start_pos + sizeof(*uregs));
@@ -660,14 +660,14 @@ static int __fpr_set(struct task_struct *target,
 	 */
 	sve_sync_to_fpsimd(target);
 
-	newstate = target->thread.fpsimd_state.user_fpsimd;
+	newstate = target->thread.fpsimd_state;
 
 	ret = user_regset_copyin(&pos, &count, &kbuf, &ubuf, &newstate,
 				 start_pos, start_pos + sizeof(newstate));
 	if (ret)
 		return ret;
 
-	target->thread.fpsimd_state.user_fpsimd = newstate;
+	target->thread.fpsimd_state = newstate;
 
 	return ret;
 }
@@ -1169,7 +1169,7 @@ static int compat_vfp_get(struct task_struct *target,
 	compat_ulong_t fpscr;
 	int ret, vregs_end_pos;
 
-	uregs = &target->thread.fpsimd_state.user_fpsimd;
+	uregs = &target->thread.fpsimd_state;
 
 	if (target == current)
 		fpsimd_preserve_current_state();
@@ -1202,7 +1202,7 @@ static int compat_vfp_set(struct task_struct *target,
 	compat_ulong_t fpscr;
 	int ret, vregs_end_pos;
 
-	uregs = &target->thread.fpsimd_state.user_fpsimd;
+	uregs = &target->thread.fpsimd_state;
 
 	vregs_end_pos = VFP_STATE_SIZE - sizeof(compat_ulong_t);
 	ret = user_regset_copyin(&pos, &count, &kbuf, &ubuf, uregs, 0,

arch/arm64/kernel/signal.c

@@ -179,8 +179,7 @@ static void __user *apply_user_offset(
 
 static int preserve_fpsimd_context(struct fpsimd_context __user *ctx)
 {
-	struct user_fpsimd_state const *fpsimd =
-		&current->thread.fpsimd_state.user_fpsimd;
+	struct user_fpsimd_state const *fpsimd = &current->thread.fpsimd_state;
 	int err;
 
 	/* copy the FP and status/control registers */

arch/arm64/kernel/signal32.c

@@ -149,8 +149,7 @@ union __fpsimd_vreg {
 
 static int compat_preserve_vfp_context(struct compat_vfp_sigframe __user *frame)
 {
-	struct user_fpsimd_state const *fpsimd =
-		&current->thread.fpsimd_state.user_fpsimd;
+	struct user_fpsimd_state const *fpsimd = &current->thread.fpsimd_state;
 	compat_ulong_t magic = VFP_MAGIC;
 	compat_ulong_t size = VFP_STORAGE_SIZE;
 	compat_ulong_t fpscr, fpexc;