arm64/sme: Implement ptrace support for streaming mode SVE registers

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>
Link: https://lore.kernel.org/r/20220419112247.711548-21-broonie@kernel.org
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

1 files changed, 1 insertions, 0 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);