KVM: arm64: Save host SVE context as appropriate

This patch adds SVE context saving to the hyp FPSIMD context switch
path.  This means that it is no longer necessary to save the host
SVE state in advance of entering the guest, when in use.

In order to avoid adding pointless complexity to the code, VHE is
assumed if SVE is in use.  VHE is an architectural prerequisite for
SVE, so there is no good reason to turn CONFIG_ARM64_VHE off in
kernels that support both SVE and KVM.

Historically, software models exist that can expose the
architecturally invalid configuration of SVE without VHE, so if
this situation is detected at kvm_init() time then KVM will be
disabled.

Signed-off-by: Dave Martin <Dave.Martin@arm.com>
Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Acked-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>

arch/arm64/Kconfig

@@ -1130,6 +1130,7 @@ endmenu
 config ARM64_SVE
 	bool "ARM Scalable Vector Extension support"
 	default y
+	depends on !KVM || ARM64_VHE
 	help
 	  The Scalable Vector Extension (SVE) is an extension to the AArch64
 	  execution state which complements and extends the SIMD functionality
@@ -1155,6 +1156,12 @@ config ARM64_SVE
 	  booting the kernel.  If unsure and you are not observing these
 	  symptoms, you should assume that it is safe to say Y.
 
+	  CPUs that support SVE are architecturally required to support the
+	  Virtualization Host Extensions (VHE), so the kernel makes no
+	  provision for supporting SVE alongside KVM without VHE enabled.
+	  Thus, you will need to enable CONFIG_ARM64_VHE if you want to support
+	  KVM in the same kernel image.
+
 config ARM64_MODULE_PLTS
 	bool
 	select HAVE_MOD_ARCH_SPECIFIC