KVM: arm64/sve: Add pseudo-register for the guest's vector lengths

This patch adds a new pseudo-register KVM_REG_ARM64_SVE_VLS to
allow userspace to set and query the set of vector lengths visible
to the guest.

In the future, multiple register slices per SVE register may be
visible through the ioctl interface.  Once the set of slices has
been determined we would not be able to allow the vector length set
to be changed any more, in order to avoid userspace seeing
inconsistent sets of registers.  For this reason, this patch adds
support for explicit finalization of the SVE configuration via the
KVM_ARM_VCPU_FINALIZE ioctl.

Finalization is the proper place to allocate the SVE register state
storage in vcpu->arch.sve_state, so this patch adds that as
appropriate.  The data is freed via kvm_arch_vcpu_uninit(), which
was previously a no-op on arm64.

To simplify the logic for determining what vector lengths can be
supported, some code is added to KVM init to work this out, in the
kvm_arm_init_arch_resources() hook.

The KVM_REG_ARM64_SVE_VLS pseudo-register is not exposed yet.
Subsequent patches will allow SVE to be turned on for guest vcpus,
making it visible.

Signed-off-by: Dave Martin <Dave.Martin@arm.com>
Reviewed-by: Julien Thierry <julien.thierry@arm.com>
Tested-by: zhang.lei <zhang.lei@jp.fujitsu.com>
Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>

1 files changed, 89 insertions, 0 deletions

diff --git a/arch/arm64/kvm/reset.c b/arch/arm64/kvm/reset.c
index f16a5f8ff2b4..e7f9c06fdbbb 100644
--- a/arch/arm64/kvm/reset.c
+++ b/arch/arm64/kvm/reset.c
@@ -23,11 +23,14 @@
 #include <linux/kvm_host.h>
 #include <linux/kvm.h>
 #include <linux/hw_breakpoint.h>
+#include <linux/slab.h>
+#include <linux/types.h>
 
 #include <kvm/arm_arch_timer.h>
 
 #include <asm/cpufeature.h>
 #include <asm/cputype.h>
+#include <asm/fpsimd.h>
 #include <asm/ptrace.h>
 #include <asm/kvm_arm.h>
 #include <asm/kvm_asm.h>
@@ -99,6 +102,92 @@ int kvm_arch_vm_ioctl_check_extension(struct kvm *kvm, long ext)
 	return r;
 }
 
+unsigned int kvm_sve_max_vl;
+
+int kvm_arm_init_arch_resources(void)
+{
+	if (system_supports_sve()) {
+		kvm_sve_max_vl = sve_max_virtualisable_vl;
+
+		/*
+		 * The get_sve_reg()/set_sve_reg() ioctl interface will need
+		 * to be extended with multiple register slice support in
+		 * order to support vector lengths greater than
+		 * SVE_VL_ARCH_MAX:
+		 */
+		if (WARN_ON(kvm_sve_max_vl > SVE_VL_ARCH_MAX))
+			kvm_sve_max_vl = SVE_VL_ARCH_MAX;
+
+		/*
+		 * Don't even try to make use of vector lengths that
+		 * aren't available on all CPUs, for now:
+		 */
+		if (kvm_sve_max_vl < sve_max_vl)
+			pr_warn("KVM: SVE vector length for guests limited to %u bytes\n",
+				kvm_sve_max_vl);
+	}
+
+	return 0;
+}
+
+/*
+ * Finalize vcpu's maximum SVE vector length, allocating
+ * vcpu->arch.sve_state as necessary.
+ */
+static int kvm_vcpu_finalize_sve(struct kvm_vcpu *vcpu)
+{
+	void *buf;
+	unsigned int vl;
+
+	vl = vcpu->arch.sve_max_vl;
+
+	/*
+	 * Resposibility for these properties is shared between
+	 * kvm_arm_init_arch_resources(), kvm_vcpu_enable_sve() and
+	 * set_sve_vls().  Double-check here just to be sure:
+	 */
+	if (WARN_ON(!sve_vl_valid(vl) || vl > sve_max_virtualisable_vl ||
+		    vl > SVE_VL_ARCH_MAX))
+		return -EIO;
+
+	buf = kzalloc(SVE_SIG_REGS_SIZE(sve_vq_from_vl(vl)), GFP_KERNEL);
+	if (!buf)
+		return -ENOMEM;
+
+	vcpu->arch.sve_state = buf;
+	vcpu->arch.flags |= KVM_ARM64_VCPU_SVE_FINALIZED;
+	return 0;
+}
+
+int kvm_arm_vcpu_finalize(struct kvm_vcpu *vcpu, int what)
+{
+	switch (what) {
+	case KVM_ARM_VCPU_SVE:
+		if (!vcpu_has_sve(vcpu))
+			return -EINVAL;
+
+		if (kvm_arm_vcpu_sve_finalized(vcpu))
+			return -EPERM;
+
+		return kvm_vcpu_finalize_sve(vcpu);
+	}
+
+	return -EINVAL;
+}
+
+bool kvm_arm_vcpu_is_finalized(struct kvm_vcpu *vcpu)
+{
+	if (vcpu_has_sve(vcpu) && !kvm_arm_vcpu_sve_finalized(vcpu))
+		return false;
+
+	return true;
+}
+
+void kvm_arch_vcpu_uninit(struct kvm_vcpu *vcpu)
+{
+	kfree(vcpu->arch.sve_state);
+}
+
 /**
  * kvm_reset_vcpu - sets core registers and sys_regs to reset value
  * @vcpu: The VCPU pointer