Re: [PATCH 15/56] KVM: arm64: Add build rules for separate VHE/nVHE object files

[Auger Eric <eric.auger@redhat.com>]

Hi David, Marc,

On 8/5/20 7:56 PM, Marc Zyngier wrote:
> From: David Brazdil <dbrazdil@google.com>
> 
> Add new folders arch/arm64/kvm/hyp/{vhe,nvhe} and Makefiles for building code
> that runs in EL2 under VHE/nVHE KVM, repsectivelly. Add an include folder for
> hyp-specific header files which will include code common to VHE/nVHE.
> 
> Build nVHE code with -D__KVM_NVHE_HYPERVISOR__, VHE code with
> -D__KVM_VHE_HYPERVISOR__.
> 
> Under nVHE 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.
> 
> The nVHE ELF symbol prefix is added to kallsyms.c as ignored. EL2-only symbols
> will never appear in EL1 stack traces.
> 
> Due to symbol prefixing, add a section in image-vars.h for aliases of symbols
> that are defined in nVHE EL2 and accessed by kernel in EL1 or vice versa.
> 
> Signed-off-by: David Brazdil <dbrazdil@google.com>
> Signed-off-by: Marc Zyngier <maz@kernel.org>
> Link: https://lore.kernel.org/r/20200625131420.71444-4-dbrazdil@google.com
> ---
>  arch/arm64/kernel/image-vars.h   | 14 +++++++++++++
>  arch/arm64/kvm/hyp/Makefile      | 10 +++++++---
>  arch/arm64/kvm/hyp/nvhe/Makefile | 34 ++++++++++++++++++++++++++++++++
>  arch/arm64/kvm/hyp/vhe/Makefile  | 17 ++++++++++++++++
>  scripts/kallsyms.c               |  1 +
>  5 files changed, 73 insertions(+), 3 deletions(-)
>  create mode 100644 arch/arm64/kvm/hyp/nvhe/Makefile
>  create mode 100644 arch/arm64/kvm/hyp/vhe/Makefile
> 
> diff --git a/arch/arm64/kernel/image-vars.h b/arch/arm64/kernel/image-vars.h
> index be0a63ffed23..3dc27da47712 100644
> --- a/arch/arm64/kernel/image-vars.h
> +++ b/arch/arm64/kernel/image-vars.h
> @@ -51,4 +51,18 @@ __efistub__ctype		= _ctype;
>  
>  #endif
>  
> +#ifdef CONFIG_KVM
> +
> +/*
> + * KVM nVHE code has its own symbol namespace prefixed with __kvm_nvhe_, to
> + * separate 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.
> + */
> +
> +#define KVM_NVHE_ALIAS(sym) __kvm_nvhe_##sym = sym;
> +
> +#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..9c5dfe6ff80b 100644
> --- a/arch/arm64/kvm/hyp/Makefile
> +++ b/arch/arm64/kvm/hyp/Makefile
> @@ -3,10 +3,14 @@
>  # Makefile for Kernel-based Virtual Machine module, HYP part
>  #
>  
> -ccflags-y += -fno-stack-protector -DDISABLE_BRANCH_PROFILING \
> -		$(DISABLE_STACKLEAK_PLUGIN)
> +incdir := $(srctree)/$(src)/include
> +subdir-asflags-y := -I$(incdir)
> +subdir-ccflags-y := -I$(incdir)				\
> +		    -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..955f4188e00f
> --- /dev/null
> +++ b/arch/arm64/kvm/hyp/nvhe/Makefile
> @@ -0,0 +1,34 @@
> +# 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__
> +
> +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/arch/arm64/kvm/hyp/vhe/Makefile b/arch/arm64/kvm/hyp/vhe/Makefile
> new file mode 100644
> index 000000000000..e04375546081
> --- /dev/null
> +++ b/arch/arm64/kvm/hyp/vhe/Makefile
> @@ -0,0 +1,17 @@
> +# SPDX-License-Identifier: GPL-2.0
> +#
> +# Makefile for Kernel-based Virtual Machine module, HYP/nVHE part
> +#
> +
> +asflags-y := -D__KVM_VHE_HYPERVISOR__
> +ccflags-y := -D__KVM_VHE_HYPERVISOR__
> +
> +obj-y :=
> +
> +# KVM 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
> 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 */
The addition of this line seems to have introduced errors on the
'vmlinux symtab matches kallsyms' perf test (perf test -v 1) which fails
on aarch64 for all __kvm_nvhe_ prefixed symbols, like

ERR : <addr> : __kvm_nvhe___invalid not on kallsyms
ERR : <addr> : __kvm_nvhe___do_hyp_init not on kallsyms
ERR : <addr> : __kvm_nvhe___kvm_handle_stub_hvc not on kallsyms
ERR : <addr> : __kvm_nvhe_reset not on kallsyms
../..

I understand we willingly hided those symbols from /proc/kallsyms. Do
you confirm the right fix is to upgrade the perf test suite accordingly?

Thanks

Eric


>  		NULL
>  	};
>  
>