Re: [PATCH v4 27/27] KVM: s390: arm64: Enable KVM_ARM64 config and Kbuild

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 4 potential issue(s) to consider:
- [High] Recompiling virt/kvm core code creates duplicate exported symbols, causing modpost failures or type confusion.
- [High] Concurrent execution of generic KVM initialization by two separate modules will clash on singleton resources like /dev/kvm.
- [High] The Makefile uses `nm -jU` and `objcopy -O default`, which are invalid for standard GNU binutils, breaking the build.
- [High] Core KVM files compiled for the arm64 module will incorrectly include the s390 architecture headers instead of arm64 headers.
--

commit 2fa0a606e2ea5038c2f6e6df6ba70d3165729ce4
Author: Steffen Eiden <seiden@linux.ibm.com>

KVM: s390: arm64: Enable KVM_ARM64 config and Kbuild

Add all Kbuild/Makefile configurations to build a second KVM module on
s390 implementing the arm64-KVM API. To prevent symbol conflicts with
kvm-s390 all internal symbols in kvm-arm64 are mangled if compiled as
built-in.

> diff --git a/arch/s390/kvm/arm64/Makefile b/arch/s390/kvm/arm64/Makefile
> new file mode 100644
> index 0000000000000..566040725ab57
> --- /dev/null
> +++ b/arch/s390/kvm/arm64/Makefile
> @@ -0,0 +1,94 @@
[ ... ]
> +include $(src)/Makefile.gen
> +
> +ccflags-y += -I $(src) -I $(objtree)/$(obj) -I$(srctree)/arch/s390/kvm/gmap -I$(srctree)/arch/arm64/include -I$(srctree)/arch/arm64/kvm -DKVM_S390_ARM64

[Severity: High]
Does this successfully override the architecture include path?

Kbuild places LINUXINCLUDE (which contains -I$(srctree)/arch/$(SRCARCH)/include
pointing to s390) before ccflags-y in the compiler invocation.

When the generic KVM code includes <asm/kvm_host.h>, will it incorrectly
resolve to the s390 header instead of the arm64 header, leading to compilation
errors or ABI mismatches?

> +
> +kvm-arm64-obj := \
> +	arm.o \

[Severity: High]
Will compiling a second copy of the core KVM logic into the system duplicate
static resource registrations?

The generic KVM initialization code in kvm_init() assumes it is a singleton
per kernel and attempts to register the /dev/kvm misc device with a fixed
minor number. If both kvm-s390 and kvm-arm64 are loaded, will the second
module's initialization fail with -EBUSY when registering the misc device?

> +	guest.o \
> +	handle_exit.o \
> +	inject_fault.o \
> +	mmu.o \
> +	mmio.o \
> +	reset.o \
> +
> +kvm-arm64-obj += $(patsubst %.o,%-arm64.o,$(kvm-y))

[Severity: High]
Does recompiling the virt/kvm core code here create duplicate exported
symbols?

When configured as modules, compiling the generic KVM core a second time
results in modpost fatal errors for exported twice symbols. When configured
as built-in, objcopy --localize-symbols modifies the symbol table but fails
to strip __ksymtab data sections, leaving duplicate KVM exports in vmlinux.

Could this lead to unpredictable symbol resolution for modules like vfio?

[ ... ]
> +LDFLAGS_kvm-unnamespaced.o := -r --whole-archive
> +$(obj)/kvm-unnamespaced.o: $(addprefix $(obj)/,$(kvm-arm64-obj)) FORCE
> +	$(call if_changed_rule,ld_o_o)
> +
> +# Make list of symbols to localize.
> +# Collect normal/exported symbols. Use dict as set for deduplication.
> +# TODO extract do script
> +quiet_cmd_nm_filter = NMFLTR  $@
> +	cmd_nm_filter = $(NM) -jU $< | sort -u > $@

[Severity: High]
Are the nm flags -jU supported by standard GNU binutils?

GNU nm lacks -j and -U, which are widely used in kernel builds. Will this
cause build failures when CONFIG_KVM_ARM64=y?

> +
> +$(obj)/kvm_symbol_list: $(obj)/kvm-unnamespaced.o FORCE
> +	$(call if_changed,nm_filter)
> +
> +define rule_oc_o_o
> +	$(call cmd_and_savecmd,objcopy)
> +	$(call cmd,gen_objtooldep)
> +	$(call cmd,gen_symversions_o)
> +endef
> +
> +OBJCOPYFLAGS_kvm-namespaced.o := -O default --localize-symbols=$(obj)/kvm_symbol_list

[Severity: High]
Is the -O default flag valid for GNU objcopy?

GNU objcopy rejects default as an invalid BFD target, which may break the
build when localizing these symbols.

> +$(obj)/kvm-namespaced.o: $(obj)/kvm-unnamespaced.o $(obj)/kvm_symbol_list FORCE
> +	$(call if_changed_rule,oc_o_o)

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260706085229.979525-1-seiden@linux.ibm.com?part=27