[PATCH v14 20/39] arm64/sme: Implement ptrace support for streaming mode SVE registers

Mark Brown
2022-04-19T11:24:57Z

The streaming mode SVE registers are represented using the same data
structures as for SVE but since the vector lengths supported and in use
may not be the same as SVE we represent them with a new type NT_ARM_SSVE.
Unfortunately we only have a single 16 bit reserved field available in
the header so there is no space to fit the current and maximum vector
length for both standard and streaming SVE mode without redefining the
structure in a way the creates a complicatd and fragile ABI. Since FFR
is not present in streaming mode it is read and written as zero.

Setting NT_ARM_SSVE registers will put the task into streaming mode,
similarly setting NT_ARM_SVE registers will exit it. Reads that do not
correspond to the current mode of the task will return the header with
no register data. For compatibility reasons on write setting no flag for
the register type will be interpreted as setting SVE registers, though
users can provide no register data as an alternative mechanism for doing
so.

Signed-off-by: Mark Brown <broonie@kernel.org>
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
---
arch/arm64/include/asm/fpsimd.h | 1 +
arch/arm64/include/uapi/asm/ptrace.h | 13 +-
arch/arm64/kernel/fpsimd.c | 31 +++-
arch/arm64/kernel/ptrace.c | 214 +++++++++++++++++++++------
include/uapi/linux/elf.h | 1 +
5 files changed, 201 insertions(+), 59 deletions(-)

diff --git a/arch/arm64/include/asm/fpsimd.h b/arch/arm64/include/asm/fpsimd.h
index 6c33bc832ed4..5afcd0709aae 100644
--- a/arch/arm64/include/asm/fpsimd.h
+++ b/arch/arm64/include/asm/fpsimd.h
@@ -144,6 +144,7 @@ struct vl_info {
extern void sve_alloc(struct task_struct *task);
extern void fpsimd_release_task(struct task_struct *task);
extern void fpsimd_sync_to_sve(struct task_struct *task);
+extern void fpsimd_force_sync_to_sve(struct task_struct *task);
extern void sve_sync_to_fpsimd(struct task_struct *task);
extern void sve_sync_from_fpsimd_zeropad(struct task_struct *task);

diff --git a/arch/arm64/include/uapi/asm/ptrace.h b/arch/arm64/include/uapi/asm/ptrace.h
index 758ae984ff97..522b925a78c1 100644
--- a/arch/arm64/include/uapi/asm/ptrace.h
+++ b/arch/arm64/include/uapi/asm/ptrace.h
@@ -109,7 +109,7 @@ struct user_hwdebug_state {
} dbg_regs[16];
};

-/* SVE/FP/SIMD state (NT_ARM_SVE) */
+/* SVE/FP/SIMD state (NT_ARM_SVE & NT_ARM_SSVE) */

struct user_sve_header {
__u32 size; /* total meaningful regset content in bytes */
@@ -220,6 +220,7 @@ struct user_sve_header {
(SVE_PT_SVE_PREG_OFFSET(vq, __SVE_NUM_PREGS) - \
SVE_PT_SVE_PREGS_OFFSET(vq))

+/* For streaming mode SVE (SSVE) FFR must be read and written as zero */
#define SVE_PT_SVE_FFR_OFFSET(vq) \
(SVE_PT_REGS_OFFSET + __SVE_FFR_OFFSET(vq))

@@ -240,10 +241,12 @@ struct user_sve_header {
- SVE_PT_SVE_OFFSET + (__SVE_VQ_BYTES - 1)) \
/ __SVE_VQ_BYTES * __SVE_VQ_BYTES)

-#define SVE_PT_SIZE(vq, flags) \
- (((flags) & SVE_PT_REGS_MASK) == SVE_PT_REGS_SVE ? \
- SVE_PT_SVE_OFFSET + SVE_PT_SVE_SIZE(vq, flags) \
- : SVE_PT_FPSIMD_OFFSET + SVE_PT_FPSIMD_SIZE(vq, flags))
+#define SVE_PT_SIZE(vq, flags) \
+ (((flags) & SVE_PT_REGS_MASK) == SVE_PT_REGS_SVE ? \
+ SVE_PT_SVE_OFFSET + SVE_PT_SVE_SIZE(vq, flags) \
+ : ((((flags) & SVE_PT_REGS_MASK) == SVE_PT_REGS_FPSIMD ? \
+ SVE_PT_FPSIMD_OFFSET + SVE_PT_FPSIMD_SIZE(vq, flags) \
+ : SVE_PT_REGS_OFFSET)))

/* pointer authentication masks (NT_ARM_PAC_MASK) */

diff --git a/arch/arm64/kernel/fpsimd.c b/arch/arm64/kernel/fpsimd.c
index 80f7ca12f855..94f06e9d37cf 100644
--- a/arch/arm64/kernel/fpsimd.c
+++ b/arch/arm64/kernel/fpsimd.c
@@ -643,7 +643,7 @@ static void fpsimd_to_sve(struct task_struct *task)
if (!system_supports_sve())
return;

- vq = sve_vq_from_vl(task_get_sve_vl(task));
+ vq = sve_vq_from_vl(thread_get_cur_vl(&task->thread));
__fpsimd_to_sve(sst, fst, vq);
}

@@ -660,7 +660,7 @@ static void fpsimd_to_sve(struct task_struct *task)
*/
static void sve_to_fpsimd(struct task_struct *task)
{
- unsigned int vq;
+ unsigned int vq, vl;
void const *sst = task->thread.sve_state;
struct user_fpsimd_state *fst = &task->thread.uw.fpsimd_state;
unsigned int i;
@@ -669,7 +669,8 @@ static void sve_to_fpsimd(struct task_struct *task)
if (!system_supports_sve())
return;

- vq = sve_vq_from_vl(task_get_sve_vl(task));
+ vl = thread_get_cur_vl(&task->thread);
+ vq = sve_vq_from_vl(vl);
for (i = 0; i < SVE_NUM_ZREGS; ++i) {
p = (__uint128_t const *)ZREG(sst, vq, i);
fst->vregs[i] = arm64_le128_to_cpu(*p);
@@ -717,6 +718,19 @@ void sve_alloc(struct task_struct *task)
}

+/*
+ * Force the FPSIMD state shared with SVE to be updated in the SVE state
+ * even if the SVE state is the current active state.
+ *
+ * This should only be called by ptrace. task must be non-runnable.
+ * task->thread.sve_state must point to at least sve_state_size(task)
+ * bytes of allocated kernel memory.
+ */
+void fpsimd_force_sync_to_sve(struct task_struct *task)
+{
+ fpsimd_to_sve(task);
+}
+
/*
* Ensure that task->thread.sve_state is up to date with respect to
* the user task, irrespective of when SVE is in use or not.
@@ -727,7 +741,8 @@ void sve_alloc(struct task_struct *task)
*/
void fpsimd_sync_to_sve(struct task_struct *task)
{
- if (!test_tsk_thread_flag(task, TIF_SVE))
+ if (!test_tsk_thread_flag(task, TIF_SVE) &&
+ !thread_sm_enabled(&task->thread))
fpsimd_to_sve(task);
}

@@ -741,7 +756,8 @@ void fpsimd_sync_to_sve(struct task_struct *task)
*/
void sve_sync_to_fpsimd(struct task_struct *task)
{
- if (test_tsk_thread_flag(task, TIF_SVE))
+ if (test_tsk_thread_flag(task, TIF_SVE) ||
+ thread_sm_enabled(&task->thread))
sve_to_fpsimd(task);
}

@@ -766,7 +782,7 @@ void sve_sync_from_fpsimd_zeropad(struct task_struct *task)
if (!test_tsk_thread_flag(task, TIF_SVE))
return;

- vq = sve_vq_from_vl(task_get_sve_vl(task));
+ vq = sve_vq_from_vl(thread_get_cur_vl(&task->thread));

memset(sst, 0, SVE_SIG_REGS_SIZE(vq));
__fpsimd_to_sve(sst, fst, vq);
@@ -810,8 +826,7 @@ int vec_set_vector_length(struct task_struct *task, enum vec_type type,
/*
* To ensure the FPSIMD bits of the SVE vector registers are preserved,
* write any live register state back to task_struct, and convert to a
- * regular FPSIMD thread. Since the vector length can only be changed
- * with a syscall we can't be in streaming mode while reconfiguring.
+ * regular FPSIMD thread.
*/
if (task == current) {
get_cpu_fpsimd_context();
diff --git a/arch/arm64/kernel/ptrace.c b/arch/arm64/kernel/ptrace.c
index 230a47b9189e..60185c27b394 100644
--- a/arch/arm64/kernel/ptrace.c
+++ b/arch/arm64/kernel/ptrace.c
@@ -713,21 +713,51 @@ static int system_call_set(struct task_struct *target,
#ifdef CONFIG_ARM64_SVE

static void sve_init_header_from_task(struct user_sve_header *header,
- struct task_struct *target)
+ struct task_struct *target,
+ enum vec_type type)
{
unsigned int vq;
+ bool active;
+ bool fpsimd_only;
+ enum vec_type task_type;

memset(header, 0, sizeof(*header));

- header->flags = test_tsk_thread_flag(target, TIF_SVE) ?
- SVE_PT_REGS_SVE : SVE_PT_REGS_FPSIMD;
- if (test_tsk_thread_flag(target, TIF_SVE_VL_INHERIT))
- header->flags |= SVE_PT_VL_INHERIT;
+ /* Check if the requested registers are active for the task */
+ if (thread_sm_enabled(&target->thread))
+ task_type = ARM64_VEC_SME;
+ else
+ task_type = ARM64_VEC_SVE;
+ active = (task_type == type);
+
+ switch (type) {
+ case ARM64_VEC_SVE:
+ if (test_tsk_thread_flag(target, TIF_SVE_VL_INHERIT))
+ header->flags |= SVE_PT_VL_INHERIT;
+ fpsimd_only = !test_tsk_thread_flag(target, TIF_SVE);
+ break;
+ case ARM64_VEC_SME:
+ if (test_tsk_thread_flag(target, TIF_SME_VL_INHERIT))
+ header->flags |= SVE_PT_VL_INHERIT;
+ fpsimd_only = false;
+ break;
+ default:
+ WARN_ON_ONCE(1);
+ return;
+ }

- header->vl = task_get_sve_vl(target);
+ if (active) {
+ if (fpsimd_only) {
+ header->flags |= SVE_PT_REGS_FPSIMD;
+ } else {
+ header->flags |= SVE_PT_REGS_SVE;
+ }
+ }
+
+ header->vl = task_get_vl(target, type);
vq = sve_vq_from_vl(header->vl);

- header->max_vl = sve_max_vl();
+ header->max_vl = vec_max_vl(type);
header->size = SVE_PT_SIZE(vq, header->flags);
header->max_size = SVE_PT_SIZE(sve_vq_from_vl(header->max_vl),
SVE_PT_REGS_SVE);
@@ -738,19 +768,17 @@ static unsigned int sve_size_from_header(struct user_sve_header const *header)
return ALIGN(header->size, SVE_VQ_BYTES);
}

-static int sve_get(struct task_struct *target,
- const struct user_regset *regset,
- struct membuf to)
+static int sve_get_common(struct task_struct *target,
+ const struct user_regset *regset,
+ struct membuf to,
+ enum vec_type type)
{
struct user_sve_header header;
unsigned int vq;
unsigned long start, end;

- if (!system_supports_sve())
- return -EINVAL;
-
/* Header */
- sve_init_header_from_task(&header, target);
+ sve_init_header_from_task(&header, target, type);
vq = sve_vq_from_vl(header.vl);

membuf_write(&to, &header, sizeof(header));
@@ -758,49 +786,61 @@ static int sve_get(struct task_struct *target,
if (target == current)
fpsimd_preserve_current_state();

- /* Registers: FPSIMD-only case */
-
BUILD_BUG_ON(SVE_PT_FPSIMD_OFFSET != sizeof(header));
- if ((header.flags & SVE_PT_REGS_MASK) == SVE_PT_REGS_FPSIMD)
+ BUILD_BUG_ON(SVE_PT_SVE_OFFSET != sizeof(header));
+
+ switch ((header.flags & SVE_PT_REGS_MASK)) {
+ case SVE_PT_REGS_FPSIMD:
return __fpr_get(target, regset, to);

- /* Otherwise: full SVE case */
+ case SVE_PT_REGS_SVE:
+ start = SVE_PT_SVE_OFFSET;
+ end = SVE_PT_SVE_FFR_OFFSET(vq) + SVE_PT_SVE_FFR_SIZE(vq);
+ membuf_write(&to, target->thread.sve_state, end - start);

- BUILD_BUG_ON(SVE_PT_SVE_OFFSET != sizeof(header));
- start = SVE_PT_SVE_OFFSET;
- end = SVE_PT_SVE_FFR_OFFSET(vq) + SVE_PT_SVE_FFR_SIZE(vq);
- membuf_write(&to, target->thread.sve_state, end - start);
+ start = end;
+ end = SVE_PT_SVE_FPSR_OFFSET(vq);
+ membuf_zero(&to, end - start);

- start = end;
- end = SVE_PT_SVE_FPSR_OFFSET(vq);
- membuf_zero(&to, end - start);
+ /*
+ * Copy fpsr, and fpcr which must follow contiguously in
+ * struct fpsimd_state:
+ */
+ start = end;
+ end = SVE_PT_SVE_FPCR_OFFSET(vq) + SVE_PT_SVE_FPCR_SIZE;
+ membuf_write(&to, &target->thread.uw.fpsimd_state.fpsr,
+ end - start);

- /*
- * Copy fpsr, and fpcr which must follow contiguously in
- * struct fpsimd_state:
- */
- start = end;
- end = SVE_PT_SVE_FPCR_OFFSET(vq) + SVE_PT_SVE_FPCR_SIZE;
- membuf_write(&to, &target->thread.uw.fpsimd_state.fpsr, end - start);
+ start = end;
+ end = sve_size_from_header(&header);
+ return membuf_zero(&to, end - start);

- start = end;
- end = sve_size_from_header(&header);
- return membuf_zero(&to, end - start);
+ default:
+ return 0;
+ }
}

-static int sve_set(struct task_struct *target,
+static int sve_get(struct task_struct *target,
const struct user_regset *regset,
- unsigned int pos, unsigned int count,
- const void *kbuf, const void __user *ubuf)
+ struct membuf to)
+{
+ if (!system_supports_sve())
+ return -EINVAL;
+
+ return sve_get_common(target, regset, to, ARM64_VEC_SVE);
+}
+
+static int sve_set_common(struct task_struct *target,
+ const struct user_regset *regset,
+ unsigned int pos, unsigned int count,
+ const void *kbuf, const void __user *ubuf,
+ enum vec_type type)
{
int ret;
struct user_sve_header header;
unsigned int vq;
unsigned long start, end;

- if (!system_supports_sve())
- return -EINVAL;
-
/* Header */
if (count < sizeof(header))
return -EINVAL;
@@ -813,13 +853,37 @@ static int sve_set(struct task_struct *target,
* Apart from SVE_PT_REGS_MASK, all SVE_PT_* flags are consumed by
* vec_set_vector_length(), which will also validate them for us:
*/
- ret = vec_set_vector_length(target, ARM64_VEC_SVE, header.vl,
+ ret = vec_set_vector_length(target, type, header.vl,
((unsigned long)header.flags & ~SVE_PT_REGS_MASK) << 16);
if (ret)
goto out;

/* Actual VL set may be less than the user asked for: */
- vq = sve_vq_from_vl(task_get_sve_vl(target));
+ vq = sve_vq_from_vl(task_get_vl(target, type));
+
+ /* Enter/exit streaming mode */
+ if (system_supports_sme()) {
+ u64 old_svcr = target->thread.svcr;
+
+ switch (type) {
+ case ARM64_VEC_SVE:
+ target->thread.svcr &= ~SYS_SVCR_EL0_SM_MASK;
+ break;
+ case ARM64_VEC_SME:
+ target->thread.svcr |= SYS_SVCR_EL0_SM_MASK;
+ break;
+ default:
+ WARN_ON_ONCE(1);
+ return -EINVAL;
+ }
+
+ /*
+ * If we switched then invalidate any existing SVE
+ * state and ensure there's storage.
+ */
+ if (target->thread.svcr != old_svcr)
+ sve_alloc(target);
+ }

/* Registers: FPSIMD-only case */

@@ -828,10 +892,15 @@ static int sve_set(struct task_struct *target,
ret = __fpr_set(target, regset, pos, count, kbuf, ubuf,
SVE_PT_FPSIMD_OFFSET);
clear_tsk_thread_flag(target, TIF_SVE);
+ if (type == ARM64_VEC_SME)
+ fpsimd_force_sync_to_sve(target);
goto out;
}

- /* Otherwise: full SVE case */
+ /*
+ * Otherwise: no registers or full SVE case. For backwards
+ * compatibility reasons we treat empty flags as SVE registers.
+ */

/*
* If setting a different VL from the requested VL and there is
@@ -852,8 +921,9 @@ static int sve_set(struct task_struct *target,

/*
* Ensure target->thread.sve_state is up to date with target's
- * FPSIMD regs, so that a short copyin leaves trailing registers
- * unmodified.
+ * FPSIMD regs, so that a short copyin leaves trailing
+ * registers unmodified. Always enable SVE even if going into
+ * streaming mode.
*/
fpsimd_sync_to_sve(target);
set_tsk_thread_flag(target, TIF_SVE);
@@ -889,8 +959,46 @@ static int sve_set(struct task_struct *target,
return ret;
}

+static int sve_set(struct task_struct *target,
+ const struct user_regset *regset,
+ unsigned int pos, unsigned int count,
+ const void *kbuf, const void __user *ubuf)
+{
+ if (!system_supports_sve())
+ return -EINVAL;
+
+ return sve_set_common(target, regset, pos, count, kbuf, ubuf,
+ ARM64_VEC_SVE);
+}
+
#endif /* CONFIG_ARM64_SVE */

+#ifdef CONFIG_ARM64_SME
+
+static int ssve_get(struct task_struct *target,
+ const struct user_regset *regset,
+ struct membuf to)
+{
+ if (!system_supports_sme())
+ return -EINVAL;
+
+ return sve_get_common(target, regset, to, ARM64_VEC_SME);
+}
+
+static int ssve_set(struct task_struct *target,
+ const struct user_regset *regset,
+ unsigned int pos, unsigned int count,
+ const void *kbuf, const void __user *ubuf)
+{
+ if (!system_supports_sme())
+ return -EINVAL;
+
+ return sve_set_common(target, regset, pos, count, kbuf, ubuf,
+ ARM64_VEC_SME);
+}
+
+#endif /* CONFIG_ARM64_SME */
+
#ifdef CONFIG_ARM64_PTR_AUTH
static int pac_mask_get(struct task_struct *target,
const struct user_regset *regset,
@@ -1108,6 +1216,9 @@ enum aarch64_regset {
#ifdef CONFIG_ARM64_SVE
REGSET_SVE,
#endif
+#ifdef CONFIG_ARM64_SVE
+ REGSET_SSVE,
+#endif
#ifdef CONFIG_ARM64_PTR_AUTH
REGSET_PAC_MASK,
REGSET_PAC_ENABLED_KEYS,
@@ -1188,6 +1299,17 @@ static const struct user_regset aarch64_regsets[] = {
.set = sve_set,
},
#endif
+#ifdef CONFIG_ARM64_SME
+ [REGSET_SSVE] = { /* Streaming mode SVE */
+ .core_note_type = NT_ARM_SSVE,
+ .n = DIV_ROUND_UP(SVE_PT_SIZE(SVE_VQ_MAX, SVE_PT_REGS_SVE),
+ SVE_VQ_BYTES),
+ .size = SVE_VQ_BYTES,
+ .align = SVE_VQ_BYTES,
+ .regset_get = ssve_get,
+ .set = ssve_set,
+ },
+#endif
#ifdef CONFIG_ARM64_PTR_AUTH
[REGSET_PAC_MASK] = {
.core_note_type = NT_ARM_PAC_MASK,
diff --git a/include/uapi/linux/elf.h b/include/uapi/linux/elf.h
index 787c657bfae8..a8dc688e1826 100644
--- a/include/uapi/linux/elf.h
+++ b/include/uapi/linux/elf.h
@@ -431,6 +431,7 @@ typedef struct elf64_shdr {
#define NT_ARM_PACG_KEYS 0x408 /* ARM pointer authentication generic key */
#define NT_ARM_TAGGED_ADDR_CTRL 0x409 /* arm64 tagged address control (prctl()) */
#define NT_ARM_PAC_ENABLED_KEYS 0x40a /* arm64 ptr auth enabled keys (prctl()) */
+#define NT_ARM_SSVE 0x40b /* ARM Streaming SVE registers */
#define NT_ARC_V2 0x600 /* ARCv2 accumulator/extra registers */
#define NT_VMCOREDD 0x700 /* Vmcore Device Dump Note */
#define NT_MIPS_DSP 0x800 /* MIPS DSP ASE registers */