[PATCH] KVM: riscv: selftests: Disable vector extension in build flags

[Yong-Xuan Wang]

Guest vCPUs never enable Vector state (sstatus.VS), so any vector
instruction traps as illegal. If the toolchain's default -march
includes the V extension, the compiler may auto-vectorize routines
like memset() into vector instructions, crashing guests.

Build with -march=rv64gc, probed the same way as x86's
-march=x86-64-v2, to ensure vector instructions are never emitted.

Signed-off-by: Yong-Xuan Wang <yongxuan.wang at sifive.com>
---
 tools/testing/selftests/kvm/Makefile.kvm | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/tools/testing/selftests/kvm/Makefile.kvm b/tools/testing/selftests/kvm/Makefile.kvm
index 6fc34e9bf8e1..46c54948f4b1 100644
--- a/tools/testing/selftests/kvm/Makefile.kvm
+++ b/tools/testing/selftests/kvm/Makefile.kvm
@@ -297,6 +297,11 @@ CFLAGS += -I$(GEN_HDRS)
 $(GEN_HDRS): $(wildcard $(arm64_tools_dir)/*)
 	$(MAKE) -C $(arm64_tools_dir) OUTPUT=$(arm64_hdr_outdir)
 endif
+ifeq ($(ARCH),riscv)
+ifeq ($(shell echo "void foo(void) { }" | $(CC) -march=rv64gc -x c - -c -o /dev/null 2>/dev/null; echo "$$?"),0)
+	CFLAGS += -march=rv64gc
+endif
+endif
 
 no-pie-option := $(call try-run, echo 'int main(void) { return 0; }' | \
         $(CC) -Werror $(CFLAGS) -no-pie -x c - -o "$$TMP", -no-pie)

---
base-commit: b5060a4aa33d7d78a8c1837ab08ef0c81ea96650
change-id: 20260831-kvm_kselftest_disable_v-23bbfab68098