arm64/sve: Rework SVE access trap to convert state in registers

When we enable SVE usage in userspace after taking a SVE access trap we
need to ensure that the portions of the register state that are not
shared with the FPSIMD registers are zeroed. Currently we do this by
forcing the FPSIMD registers to be saved to the task struct and converting
them there. This is wasteful in the common case where the task state is
loaded into the registers and we will immediately return to userspace
since we can initialise the SVE state directly in registers instead of
accessing multiple copies of the register state in memory.

Instead in that common case do the conversion in the registers and
update the task metadata so that we can return to userspace without
spilling the register state to memory unless there is some other reason
to do so.

Signed-off-by: Mark Brown <broonie@kernel.org>
Link: https://lore.kernel.org/r/20210312190313.24598-1-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 bec5f14b622a..ebb263b2d3b1 100644
--- a/arch/arm64/include/asm/fpsimd.h
+++ b/arch/arm64/include/asm/fpsimd.h
@@ -73,6 +73,7 @@ extern void sve_flush_live(void);
 extern void sve_load_from_fpsimd_state(struct user_fpsimd_state const *state,
 				       unsigned long vq_minus_1);
 extern unsigned int sve_get_vl(void);
+extern void sve_set_vq(unsigned long vq_minus_1);
 
 struct arm64_cpu_capabilities;
 extern void sve_kernel_enable(const struct arm64_cpu_capabilities *__unused);