KVM: Don't pre-reserve xarray entries when storing empty/NULL attributesgrafted

Skip the xarray reservation loop when clearing all memory attributes, as
storing NULL only erases the entry and never needs to allocate, so no
reservation (and no cleanup of a failed one) is required in that case.

Suggested-by: Sean Christopherson <seanjc@google.com>
Cc: David Ballesteros <davimaba.v@proton.me>
Signed-off-by: Zeng Chi <zengchi@kylinos.cn>
Link: https://patch.msgid.link/20260921102442.1232375-1-zeng_chi911@163.com
[sean: split to separate patch]
Signed-off-by: Sean Christopherson <seanjc@google.com>

1 files changed, 53 insertions, 0 deletions

diff --git a/arch/mips/kvm/hypcall.c b/arch/mips/kvm/hypcall.c
new file mode 100644
index 000000000..830634351
--- /dev/null
+++ b/arch/mips/kvm/hypcall.c
@@ -0,0 +1,53 @@
+/*
+ * This file is subject to the terms and conditions of the GNU General Public
+ * License.  See the file "COPYING" in the main directory of this archive
+ * for more details.
+ *
+ * KVM/MIPS: Hypercall handling.
+ *
+ * Copyright (C) 2015  Imagination Technologies Ltd.
+ */
+
+#include <linux/kernel.h>
+#include <linux/kvm_host.h>
+#include <linux/kvm_para.h>
+
+#define MAX_HYPCALL_ARGS	4
+
+enum emulation_result kvm_mips_emul_hypcall(struct kvm_vcpu *vcpu,
+					    union mips_instruction inst)
+{
+	unsigned int code = (inst.co_format.code >> 5) & 0x3ff;
+
+	kvm_debug("[%#lx] HYPCALL %#03x\n", vcpu->arch.pc, code);
+
+	switch (code) {
+	case 0:
+		return EMULATE_HYPERCALL;
+	default:
+		return EMULATE_FAIL;
+	};
+}
+
+static int kvm_mips_hypercall(struct kvm_vcpu *vcpu, unsigned long num,
+			      const unsigned long *args, unsigned long *hret)
+{
+	/* Report unimplemented hypercall to guest */
+	*hret = -KVM_ENOSYS;
+	return RESUME_GUEST;
+}
+
+int kvm_mips_handle_hypcall(struct kvm_vcpu *vcpu)
+{
+	unsigned long num, args[MAX_HYPCALL_ARGS];
+
+	/* read hypcall number and arguments */
+	num = vcpu->arch.gprs[2];	/* v0 */
+	args[0] = vcpu->arch.gprs[4];	/* a0 */
+	args[1] = vcpu->arch.gprs[5];	/* a1 */
+	args[2] = vcpu->arch.gprs[6];	/* a2 */
+	args[3] = vcpu->arch.gprs[7];	/* a3 */
+
+	return kvm_mips_hypercall(vcpu, num,
+				  args, &vcpu->arch.gprs[2] /* v0 */);
+}