KVM: arm64: pkvm: Remove struct cpu_sve_state

KVM: arm64: pkvm: Remove struct cpu_sve_state

There's no need for struct cpu_sve_state. Code would be simpler and more
robust without it, and removing it will simplify further cleanups (e.g.
adding an opaque type for the sve register state).

Protected KVM stores most of the host's system register state in
kvm_host_data::host_ctxt, which is an instance of struct
kvm_cpu_context. As kvm_cpu_context::sys_regs[] has a slot for ZCR_EL1,
we can store the host's ZCR_EL1 there.

While kvm_cpu_context::sys_regs doesn't have slots for FPSR and FPCR,
these are usually expected to be stored in struct user_fpsimd_state.
For historical reasons, __sve_save_state and __sve_restore_state()
expect a pointer to fpsr *within* struct user_fpsimd_state, assuming the
fpcr will immediately follow, as per the order within struct
user_fpsimd_state. We currently match this ordering in struct
cpu_sve_state, but it would be simpler and more robust to use struct
user_fpsimd_state directly.

After moving ZCR_EL1, FPSR, and FPCR out of struct cpu_sve_state, all
that's left is sve_regs, which can be represented as a pointer without
need for a container struct. This is kept as a pointer to u8 (matching
the array type), as this permits the compiler to catch unbalanced
referencing/dereferencing, which is not possible for pointers to void.

Apply the above changes, and remove cpu_sve_state.

I've dropped the comment regarding buffer alignment as AFAICT this was
never necessary. The LDR/STR (vector) instructions only require this
alignment when SCTLR_ELx.A==1, which is not the case for the kernel or
hyp code. Nothing else depends on the alignment.

Signed-off-by: Mark Rutland <mark.rutland@arm.com>
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: Mark Brown <broonie@kernel.org>
Cc: Oliver Upton <oupton@kernel.org>
Cc: Will Deacon <will@kernel.org>
Signed-off-by: Will Deacon <will@kernel.org>