[PATCH v2 06/19] KVM: arm64: selftests: Add protected-VM boot trampoline

[Fuad Tabba <fuad.tabba@linux.dev>]

From: Will Deacon <will@kernel.org>

EL2 takes only PC and X0 from the host when it boots a protected vCPU,
and resets everything else. So the registers the selftest library sets
before the first run never reach the guest.

Boot a protected guest through a trampoline that restores X0-X7, seven
EL1 system registers and the stack pointer from a block X0 points to,
then enables the MMU and branches to the guest's entry point.

Signed-off-by: Will Deacon <will@kernel.org>
Reviewed-by: Joey Gouly <joey.gouly@arm.com>
Signed-off-by: Fuad Tabba <fuad.tabba@linux.dev>
---
 tools/testing/selftests/kvm/Makefile.kvm      |  1 +
 .../selftests/kvm/include/arm64/pkvm.h        | 49 ++++++++++++++++
 .../selftests/kvm/lib/arm64/pvm-entry.S       | 57 +++++++++++++++++++
 3 files changed, 107 insertions(+)
 create mode 100644 tools/testing/selftests/kvm/include/arm64/pkvm.h
 create mode 100644 tools/testing/selftests/kvm/lib/arm64/pvm-entry.S

diff --git a/tools/testing/selftests/kvm/Makefile.kvm b/tools/testing/selftests/kvm/Makefile.kvm
index 17a4256e90819..c254e82f9a786 100644
--- a/tools/testing/selftests/kvm/Makefile.kvm
+++ b/tools/testing/selftests/kvm/Makefile.kvm
@@ -35,6 +35,7 @@ LIBKVM_arm64 += lib/arm64/gic_v3.c
 LIBKVM_arm64 += lib/arm64/gic_v3_its.c
 LIBKVM_arm64 += lib/arm64/handlers.S
 LIBKVM_arm64 += lib/arm64/processor.c
+LIBKVM_arm64 += lib/arm64/pvm-entry.S
 LIBKVM_arm64 += lib/arm64/spinlock.c
 LIBKVM_arm64 += lib/arm64/ucall.c
 LIBKVM_arm64 += lib/arm64/vgic.c
diff --git a/tools/testing/selftests/kvm/include/arm64/pkvm.h b/tools/testing/selftests/kvm/include/arm64/pkvm.h
new file mode 100644
index 0000000000000..29600342eca13
--- /dev/null
+++ b/tools/testing/selftests/kvm/include/arm64/pkvm.h
@@ -0,0 +1,49 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Copyright (C) 2025 Google LLC
+ * Author: Will Deacon <will@kernel.org>
+ */
+
+#ifndef SELFTEST_KVM_ARM64_PKVM_H
+#define SELFTEST_KVM_ARM64_PKVM_H
+
+#ifndef __ASSEMBLER__
+/*
+ * Register state the boot trampoline (pvm-entry.S) restores. Only PC and X0
+ * survive to a protected guest's first run, so X0 points at this block.
+ */
+struct pvm_boot_args {
+	u64	jump_tgt;
+
+	u64	regs[8];
+	u64	cpacr_el1;
+	u64	sctlr_el1;
+	u64	tcr_el1;
+	u64	mair_el1;
+	u64	ttbr0_el1;
+	u64	vbar_el1;
+
+	u64	tpidr_el1;
+	u64	sp_el1;
+};
+#endif
+
+#define PVM_BOOT_ARGS_OFF_JUMP_TGT	0
+#define PVM_BOOT_ARGS_OFF_X0		(PVM_BOOT_ARGS_OFF_JUMP_TGT + 8)
+#define PVM_BOOT_ARGS_OFF_X1		(PVM_BOOT_ARGS_OFF_X0 + 8)
+#define PVM_BOOT_ARGS_OFF_X2		(PVM_BOOT_ARGS_OFF_X1 + 8)
+#define PVM_BOOT_ARGS_OFF_X3		(PVM_BOOT_ARGS_OFF_X2 + 8)
+#define PVM_BOOT_ARGS_OFF_X4		(PVM_BOOT_ARGS_OFF_X3 + 8)
+#define PVM_BOOT_ARGS_OFF_X5		(PVM_BOOT_ARGS_OFF_X4 + 8)
+#define PVM_BOOT_ARGS_OFF_X6		(PVM_BOOT_ARGS_OFF_X5 + 8)
+#define PVM_BOOT_ARGS_OFF_X7		(PVM_BOOT_ARGS_OFF_X6 + 8)
+#define PVM_BOOT_ARGS_OFF_CPACR_EL1	(PVM_BOOT_ARGS_OFF_X7 + 8)
+#define PVM_BOOT_ARGS_OFF_SCTLR_EL1	(PVM_BOOT_ARGS_OFF_CPACR_EL1 + 8)
+#define PVM_BOOT_ARGS_OFF_TCR_EL1	(PVM_BOOT_ARGS_OFF_SCTLR_EL1 + 8)
+#define PVM_BOOT_ARGS_OFF_MAIR_EL1	(PVM_BOOT_ARGS_OFF_TCR_EL1 + 8)
+#define PVM_BOOT_ARGS_OFF_TTBR0_EL1	(PVM_BOOT_ARGS_OFF_MAIR_EL1 + 8)
+#define PVM_BOOT_ARGS_OFF_VBAR_EL1	(PVM_BOOT_ARGS_OFF_TTBR0_EL1 + 8)
+#define PVM_BOOT_ARGS_OFF_TPIDR_EL1	(PVM_BOOT_ARGS_OFF_VBAR_EL1 + 8)
+#define PVM_BOOT_ARGS_OFF_SP_EL1	(PVM_BOOT_ARGS_OFF_TPIDR_EL1 + 8)
+
+#endif /* SELFTEST_KVM_ARM64_PKVM_H */
diff --git a/tools/testing/selftests/kvm/lib/arm64/pvm-entry.S b/tools/testing/selftests/kvm/lib/arm64/pvm-entry.S
new file mode 100644
index 0000000000000..d00abe03f8f84
--- /dev/null
+++ b/tools/testing/selftests/kvm/lib/arm64/pvm-entry.S
@@ -0,0 +1,57 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Copyright (C) 2025 Google LLC
+ * Author: Will Deacon <will@kernel.org>
+ */
+
+#include "pkvm.h"
+
+	.text
+	.balign 16
+	.globl	pvm_entry_start
+pvm_entry_start:
+	mov	x30, x0
+
+	ldr	x0, [x30, #PVM_BOOT_ARGS_OFF_X0]
+	ldr	x1, [x30, #PVM_BOOT_ARGS_OFF_X1]
+	ldr	x2, [x30, #PVM_BOOT_ARGS_OFF_X2]
+	ldr	x3, [x30, #PVM_BOOT_ARGS_OFF_X3]
+	ldr	x4, [x30, #PVM_BOOT_ARGS_OFF_X4]
+	ldr	x5, [x30, #PVM_BOOT_ARGS_OFF_X5]
+	ldr	x6, [x30, #PVM_BOOT_ARGS_OFF_X6]
+	ldr	x7, [x30, #PVM_BOOT_ARGS_OFF_X7]
+
+	ldr	x8, [x30, #PVM_BOOT_ARGS_OFF_JUMP_TGT]
+
+	ldr	x9, [x30, #PVM_BOOT_ARGS_OFF_CPACR_EL1]
+	msr	cpacr_el1, x9
+
+	ldr	x9, [x30, #PVM_BOOT_ARGS_OFF_TCR_EL1]
+	msr	tcr_el1, x9
+
+	ldr	x9, [x30, #PVM_BOOT_ARGS_OFF_MAIR_EL1]
+	msr	mair_el1, x9
+
+	ldr	x9, [x30, #PVM_BOOT_ARGS_OFF_TTBR0_EL1]
+	msr	ttbr0_el1, x9
+
+	ldr	x9, [x30, #PVM_BOOT_ARGS_OFF_VBAR_EL1]
+	msr	vbar_el1, x9
+
+	ldr	x9, [x30, #PVM_BOOT_ARGS_OFF_TPIDR_EL1]
+	msr	tpidr_el1, x9
+
+	ldr	x9, [x30, #PVM_BOOT_ARGS_OFF_SP_EL1]
+	mov	sp, x9
+
+	/* No stale TLB entries, and the writes above in effect, before the MMU is on. */
+	tlbi	vmalle1
+	dsb	nsh
+	isb
+	ldr	x9, [x30, #PVM_BOOT_ARGS_OFF_SCTLR_EL1]
+	msr	sctlr_el1, x9
+	isb
+
+	br	x8
+	.globl	pvm_entry_end
+pvm_entry_end:
-- 
2.47.3