arm64: fpsimd: Use opaque type for SVE state

As the SVE state size can vary at runtime, we don't have a concrete type
for the in-memory SVE state, and pass this around using a pointer to
void. The functions which save/restore the SVE state have a very unusual
calling convention, expecting a pointer to the FFR *in the middle of*
the in-memory SVE state, which is also passed as a pointer to void.
Passing a pointer to the FFR also requires that callers find the live VL
and perform some arithmetic, which callers implement differently.

Using pointer to void means that it's very easy to introduce errors that
cannot be caught by the compiler (e.g. as 'void **' can be assigned to
'void *'). In general this is unnecessarily confusing and fragile.

Improve this by adding an opaque 'struct arm64_sve_state', and
consistently passing a pointer to this, performing the necessary
offsetting *within* the save/restore functions.

For the moment, the offsetting is performed in a new '_sve_pffr'
assembly macro, using the ADDVL and ADDPL instructions. These add a
multiple of the live vector length and predicate length respectively.
The ADDVL immediate range cannot encode 32, so this is split into two
increments of 16.

Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Reviewed-by: Mark Brown <broonie@kernel.org>
Reviewed-by: Vladimir Murzin <vladimir.murzin@arm.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Fuad Tabba <tabba@google.com>
Cc: James Morse <james.morse@arm.com>
Cc: Marc Zyngier <maz@kernel.org>
Cc: Oliver Upton <oupton@kernel.org>
Cc: Will Deacon <will@kernel.org>
Signed-off-by: Will Deacon <will@kernel.org>

1 files changed, 10 insertions, 11 deletions

diff --git a/arch/arm64/kernel/fpsimd.c b/arch/arm64/kernel/fpsimd.c
index 9806fea8fea7..0da2f75de5dd 100644
--- a/arch/arm64/kernel/fpsimd.c
+++ b/arch/arm64/kernel/fpsimd.c
@@ -425,8 +425,7 @@ static void task_fpsimd_load(void)
 
 	if (restore_sve_regs) {
 		WARN_ON_ONCE(current->thread.fp_type != FP_STATE_SVE);
-		sve_load_state(sve_pffr(&current->thread),
-			       restore_ffr);
+		sve_load_state(current->thread.sve_state, restore_ffr);
 		fpsimd_load_common(&current->thread.uw.fpsimd_state);
 	} else {
 		WARN_ON_ONCE(current->thread.fp_type != FP_STATE_FPSIMD);
@@ -507,9 +506,7 @@ static void fpsimd_save_user_state(void)
 			return;
 		}
 
-		sve_save_state((char *)last->sve_state +
-					sve_ffr_offset(vl),
-			       save_ffr);
+		sve_save_state(last->sve_state, save_ffr);
 		fpsimd_save_common(last->st);
 		*last->fp_type = FP_STATE_SVE;
 	} else {
@@ -641,7 +638,8 @@ static __uint128_t arm64_cpu_to_le128(__uint128_t x)
 
 #define arm64_le128_to_cpu(x) arm64_cpu_to_le128(x)
 
-static void __fpsimd_to_sve(void *sst, struct user_fpsimd_state const *fst,
+static void __fpsimd_to_sve(struct arm64_sve_state *sst,
+			    struct user_fpsimd_state const *fst,
 			    unsigned int vq)
 {
 	unsigned int i;
@@ -668,7 +666,7 @@ static void __fpsimd_to_sve(void *sst, struct user_fpsimd_state const *fst,
 static inline void fpsimd_to_sve(struct task_struct *task)
 {
 	unsigned int vq;
-	void *sst = task->thread.sve_state;
+	struct arm64_sve_state *sst = task->thread.sve_state;
 	struct user_fpsimd_state const *fst = &task->thread.uw.fpsimd_state;
 
 	if (!system_supports_sve() && !system_supports_sme())
@@ -692,7 +690,7 @@ static inline void fpsimd_to_sve(struct task_struct *task)
 static inline void sve_to_fpsimd(struct task_struct *task)
 {
 	unsigned int vq, vl;
-	void const *sst = task->thread.sve_state;
+	const struct arm64_sve_state *sst = task->thread.sve_state;
 	struct user_fpsimd_state *fst = &task->thread.uw.fpsimd_state;
 	unsigned int i;
 	__uint128_t const *p;
@@ -791,7 +789,7 @@ void fpsimd_sync_from_effective_state(struct task_struct *task)
 void fpsimd_sync_to_effective_state_zeropad(struct task_struct *task)
 {
 	unsigned int vq;
-	void *sst = task->thread.sve_state;
+	struct arm64_sve_state *sst = task->thread.sve_state;
 	struct user_fpsimd_state const *fst = &task->thread.uw.fpsimd_state;
 
 	if (task->thread.fp_type != FP_STATE_SVE)
@@ -809,7 +807,8 @@ static int change_live_vector_length(struct task_struct *task,
 {
 	unsigned int sve_vl = task_get_sve_vl(task);
 	unsigned int sme_vl = task_get_sme_vl(task);
-	void *sve_state = NULL, *sme_state = NULL;
+	struct arm64_sve_state *sve_state = NULL;
+	void *sme_state = NULL;
 
 	if (type == ARM64_VEC_SME)
 		sme_vl = vl;
@@ -1645,7 +1644,7 @@ static void fpsimd_flush_thread_vl(enum vec_type type)
 
 void fpsimd_flush_thread(void)
 {
-	void *sve_state = NULL;
+	struct arm64_sve_state *sve_state = NULL;
 	void *sme_state = NULL;
 
 	if (!system_supports_fpsimd())