[PATCH 05/37] KVM: arm64: nVHE: Break out of the hyp-init idmap

From: Andrew Scull <ascull@google.com>
To: kvmarm@lists.cs.columbia.edu
Cc: maz@kernel.org, kernel-team@android.com
Subject: [PATCH 05/37] KVM: arm64: nVHE: Break out of the hyp-init idmap
Date: Wed, 15 Jul 2020 19:44:06 +0100	[thread overview]
Message-ID: <20200715184438.1390996-6-ascull@google.com> (raw)
In-Reply-To: <20200715184438.1390996-1-ascull@google.com>

The idmap is a restrictive context as it is located separately from the
rest of hyp. Extra care must be taken to avoid symbol references that
will not resolve correctly so, the less that has to be done in this
context, the better.

To overcome this, pass an pre-resolved pointer into hyp-init that it can
jump to and escape the idmap once it has installed the page table.

This patch just introduces the mechanism to break out of the idmap for
use in future changes.

Signed-off-by: Andrew Scull <ascull@google.com>
---
 arch/arm64/kvm/arm.c                |  7 ++++++-
 arch/arm64/kvm/hyp/nvhe/Makefile    |  3 ++-
 arch/arm64/kvm/hyp/nvhe/hyp-init.S  | 13 +++++++------
 arch/arm64/kvm/hyp/nvhe/hyp-start.S | 16 ++++++++++++++++
 4 files changed, 31 insertions(+), 8 deletions(-)
 create mode 100644 arch/arm64/kvm/hyp/nvhe/hyp-start.S

diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c
index bf662c0dd409..52be6149fcbf 100644
--- a/arch/arm64/kvm/arm.c
+++ b/arch/arm64/kvm/arm.c
@@ -1257,9 +1257,12 @@ long kvm_arch_vm_ioctl(struct file *filp,
 
 static void cpu_init_hyp_mode(void)
 {
+	DECLARE_KVM_NVHE_SYM(__kvm_hyp_start);
+
 	phys_addr_t pgd_ptr;
 	unsigned long hyp_stack_ptr;
 	unsigned long vector_ptr;
+	unsigned long start_hyp;
 	unsigned long tpidr_el2;
 
 	/* Switch from the HYP stub to our own HYP init vector */
@@ -1277,6 +1280,7 @@ static void cpu_init_hyp_mode(void)
 	hyp_stack_ptr = __this_cpu_read(kvm_arm_hyp_stack_page) + PAGE_SIZE;
 	hyp_stack_ptr = kern_hyp_va(hyp_stack_ptr);
 	vector_ptr = (unsigned long)kvm_get_hyp_vector();
+	start_hyp = (unsigned long)kern_hyp_va(kvm_ksym_ref_nvhe(__kvm_hyp_start));
 
 	/*
 	 * Call initialization code, and switch to the full blown HYP code.
@@ -1285,7 +1289,8 @@ static void cpu_init_hyp_mode(void)
 	 * cpus_have_const_cap() wrapper.
 	 */
 	BUG_ON(!system_capabilities_finalized());
-	__kvm_call_hyp((void *)pgd_ptr, hyp_stack_ptr, vector_ptr, tpidr_el2);
+	__kvm_call_hyp((void *)pgd_ptr, hyp_stack_ptr, vector_ptr, start_hyp,
+		       tpidr_el2);
 
 	/*
 	 * Disabling SSBD on a non-VHE system requires us to enable SSBS
diff --git a/arch/arm64/kvm/hyp/nvhe/Makefile b/arch/arm64/kvm/hyp/nvhe/Makefile
index 0b34414557d6..1f3a39efaa6e 100644
--- a/arch/arm64/kvm/hyp/nvhe/Makefile
+++ b/arch/arm64/kvm/hyp/nvhe/Makefile
@@ -6,7 +6,8 @@
 asflags-y := -D__KVM_NVHE_HYPERVISOR__
 ccflags-y := -D__KVM_NVHE_HYPERVISOR__
 
-obj-y := timer-sr.o sysreg-sr.o debug-sr.o switch.o tlb.o hyp-init.o
+obj-y := timer-sr.o sysreg-sr.o debug-sr.o switch.o tlb.o hyp-init.o \
+	 hyp-start.o
 obj-y += ../vgic-v3-sr.o ../aarch32.o ../vgic-v2-cpuif-proxy.o ../entry.o \
 	 ../fpsimd.o ../hyp-entry.o
 
diff --git a/arch/arm64/kvm/hyp/nvhe/hyp-init.S b/arch/arm64/kvm/hyp/nvhe/hyp-init.S
index f80f169a8442..029c51365d03 100644
--- a/arch/arm64/kvm/hyp/nvhe/hyp-init.S
+++ b/arch/arm64/kvm/hyp/nvhe/hyp-init.S
@@ -46,13 +46,17 @@ __invalid:
 	 * x0: HYP pgd
 	 * x1: HYP stack
 	 * x2: HYP vectors
-	 * x3: per-CPU offset
+	 * x3: __kvm_hyp_start HYP address
+	 * x4: per-CPU offset
 	 */
 __do_hyp_init:
 	/* Check for a stub HVC call */
 	cmp	x0, #HVC_STUB_HCALL_NR
 	b.lo	__kvm_handle_stub_hvc
 
+	/* Set tpidr_el2 for use by HYP */
+	msr	tpidr_el2, x4
+
 	phys_to_ttbr x4, x0
 alternative_if ARM64_HAS_CNP
 	orr	x4, x4, #TTBR_CNP_BIT
@@ -116,11 +120,8 @@ alternative_else_nop_endif
 	mov	sp, x1
 	msr	vbar_el2, x2
 
-	/* Set tpidr_el2 for use by HYP */
-	msr	tpidr_el2, x3
-
-	/* Hello, World! */
-	eret
+	/* Leave the idmap posthaste and head over to __kvm_hyp_start */
+	br	x3
 SYM_CODE_END(__kvm_hyp_init)
 
 SYM_CODE_START(__kvm_handle_stub_hvc)
diff --git a/arch/arm64/kvm/hyp/nvhe/hyp-start.S b/arch/arm64/kvm/hyp/nvhe/hyp-start.S
new file mode 100644
index 000000000000..5f7fbcb57fd5
--- /dev/null
+++ b/arch/arm64/kvm/hyp/nvhe/hyp-start.S
@@ -0,0 +1,16 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ * Copyright (C) 2020 - Google Inc
+ * Author: Andrew Scull <ascull@google.com>
+ */
+
+#include <linux/linkage.h>
+
+#include <asm/assembler.h>
+#include <asm/asm-offsets.h>
+#include <asm/kvm_asm.h>
+
+SYM_CODE_START(__kvm_hyp_start)
+	/* Hello, World! */
+	eret
+SYM_CODE_END(__kvm_hyp_start)
-- 
2.27.0.389.gc38d7665816-goog

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