Re: [PATCH v3 03/15] arm64: kvm: Add build rules for separate nVHE object files

Add new folder arch/arm64/kvm/hyp/nvhe and a Makefile for building code 
that
runs in EL2 under nVHE KVM.

Compile each source file into a `.hyp.tmp.o` object first, then prefix 
all
its symbols with "__kvm_nvhe_" using `objcopy` and produce a `.hyp.o`.
Suffixes were chosen so that it would be possible for VHE and nVHE to 
share
some source files, but compiled with different CFLAGS. nVHE build rules 
add
-D__KVM_NVHE_HYPERVISOR__.

The nVHE ELF symbol prefix is added to kallsyms.c as ignored. EL2-only 
symbols
will never appear in EL1 stack traces.

Signed-off-by: David Brazdil <redacted>
---
 arch/arm64/kernel/image-vars.h   | 12 +++++++++++
 arch/arm64/kvm/hyp/Makefile      |  2 +-
 arch/arm64/kvm/hyp/nvhe/Makefile | 35 ++++++++++++++++++++++++++++++++
 scripts/kallsyms.c               |  1 +
 4 files changed, 49 insertions(+), 1 deletion(-)
 create mode 100644 arch/arm64/kvm/hyp/nvhe/Makefile

diff --git a/arch/arm64/kernel/image-vars.h 

b/arch/arm64/kernel/image-vars.h
index be0a63ffed23..f32b406e90c0 100644

--- a/arch/arm64/kernel/image-vars.h
+++ b/arch/arm64/kernel/image-vars.h

@@ -51,4 +51,16 @@ __efistub__ctype		= _ctype;

 #endif

+#ifdef CONFIG_KVM
+
+/*
+ * KVM nVHE code has its own symbol namespace prefixed by __kvm_nvhe_, 

to
+ * isolate it from the kernel proper. The following symbols are 
legally
+ * accessed by it, therefore provide aliases to make them linkable.
+ * Do not include symbols which may not be safely accessed under 
hypervisor
+ * memory mappings.
+ */
+
+#endif /* CONFIG_KVM */
+
 #endif /* __ARM64_KERNEL_IMAGE_VARS_H */

diff --git a/arch/arm64/kvm/hyp/Makefile b/arch/arm64/kvm/hyp/Makefile
index 5d8357ddc234..5f4f217532e0 100644
--- a/arch/arm64/kvm/hyp/Makefile
+++ b/arch/arm64/kvm/hyp/Makefile

@@ -6,7 +6,7 @@
 ccflags-y += -fno-stack-protector -DDISABLE_BRANCH_PROFILING \
 		$(DISABLE_STACKLEAK_PLUGIN)

-obj-$(CONFIG_KVM) += hyp.o
+obj-$(CONFIG_KVM) += hyp.o nvhe/
 obj-$(CONFIG_KVM_INDIRECT_VECTORS) += smccc_wa.o

 hyp-y := vgic-v3-sr.o timer-sr.o aarch32.o vgic-v2-cpuif-proxy.o 

sysreg-sr.o \

diff --git a/arch/arm64/kvm/hyp/nvhe/Makefile 

b/arch/arm64/kvm/hyp/nvhe/Makefile
new file mode 100644
index 000000000000..7d64235dba62

--- /dev/null
+++ b/arch/arm64/kvm/hyp/nvhe/Makefile

@@ -0,0 +1,35 @@
+# SPDX-License-Identifier: GPL-2.0
+#
+# Makefile for Kernel-based Virtual Machine module, HYP/nVHE part
+#
+
+asflags-y := -D__KVM_NVHE_HYPERVISOR__
+ccflags-y := -D__KVM_NVHE_HYPERVISOR__ -fno-stack-protector \
+	     -DDISABLE_BRANCH_PROFILING $(DISABLE_STACKLEAK_PLUGIN)
+
+obj-y :=
+
+obj-y := $(patsubst %.o,%.hyp.o,$(obj-y))
+extra-y := $(patsubst %.hyp.o,%.hyp.tmp.o,$(obj-y))
+
+$(obj)/%.hyp.tmp.o: $(src)/%.c FORCE
+	$(call if_changed_rule,cc_o_c)
+$(obj)/%.hyp.tmp.o: $(src)/%.S FORCE
+	$(call if_changed_rule,as_o_S)
+$(obj)/%.hyp.o: $(obj)/%.hyp.tmp.o FORCE
+	$(call if_changed,hypcopy)
+
+quiet_cmd_hypcopy = HYPCOPY $@
+      cmd_hypcopy = $(OBJCOPY) --prefix-symbols=__kvm_nvhe_ $< $@
+
+# KVM nVHE code is run at a different exception code with a different 

map, so
+# compiler instrumentation that inserts callbacks or checks into the 
code may
+# cause crashes. Just disable it.
+GCOV_PROFILE	:= n
+KASAN_SANITIZE	:= n
+UBSAN_SANITIZE	:= n
+KCOV_INSTRUMENT	:= n
+
+# Skip objtool checking for this directory because nVHE code is 
compiled with
+# non-standard build rules.
+OBJECT_FILES_NON_STANDARD := y

diff --git a/scripts/kallsyms.c b/scripts/kallsyms.c
index 6dc3078649fa..0096cd965332 100644
--- a/scripts/kallsyms.c
+++ b/scripts/kallsyms.c

@@ -109,6 +109,7 @@ static bool is_ignored_symbol(const char *name, 

char type)
 		".LASANPC",		/* s390 kasan local symbols */
 		"__crc_",		/* modversions */
 		"__efistub_",		/* arm64 EFI stub namespace */
+		"__kvm_nvhe_",		/* arm64 non-VHE KVM namespace */
 		NULL
 	};