linux-kernel - [RFC PATCH v1] KVM: selftests: Compile s390 tests with -march=z10

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Date:   Fri, 27 Jan 2023 18:45:52 +0100
From:   Nina Schoetterl-Glausch <nsg@...ux.ibm.com>
To:     Paolo Bonzini <pbonzini@...hat.com>, Shuah Khan <shuah@...nel.org>,
        Janosch Frank <frankja@...ux.ibm.com>,
        Claudio Imbrenda <imbrenda@...ux.ibm.com>
Cc:     Nina Schoetterl-Glausch <nsg@...ux.ibm.com>, kvm@...r.kernel.org,
        linux-kselftest@...r.kernel.org, linux-kernel@...r.kernel.org,
        Thomas Huth <thuth@...hat.com>
Subject: [RFC PATCH v1] KVM: selftests: Compile s390 tests with -march=z10

The guest used in s390 kvm selftests is not be set up to handle all
instructions the compiler might emit, i.e. vector instructions, leading
to crashes.
Limit what the compiler emits to the oldest machine model currently
supported by Linux.

Signed-off-by: Nina Schoetterl-Glausch <nsg@...ux.ibm.com>
---


Should we also set -mtune?
Since it are vector instructions that caused the problem here, there
are some alternatives:
 * use -mno-vx
 * set the required guest control bit to enable vector instructions on
   models supporting them

-march=z10 might prevent similar issues with other instructions, but I
don't know if there actually exist other relevant instructions, so it
could be needlessly restricting.


 tools/testing/selftests/kvm/Makefile | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/tools/testing/selftests/kvm/Makefile b/tools/testing/selftests/kvm/Makefile
index 1750f91dd936..df0989949eb5 100644
--- a/tools/testing/selftests/kvm/Makefile
+++ b/tools/testing/selftests/kvm/Makefile
@@ -200,6 +200,9 @@ CFLAGS += -Wall -Wstrict-prototypes -Wuninitialized -O2 -g -std=gnu99 \
 	-I$(LINUX_TOOL_ARCH_INCLUDE) -I$(LINUX_HDR_PATH) -Iinclude \
 	-I$(<D) -Iinclude/$(ARCH_DIR) -I ../rseq -I.. $(EXTRA_CFLAGS) \
 	$(KHDR_INCLUDES)
+ifeq ($(ARCH),s390)
+	CFLAGS += -march=z10
+endif
 
 no-pie-option := $(call try-run, echo 'int main(void) { return 0; }' | \
         $(CC) -Werror $(CFLAGS) -no-pie -x c - -o "$$TMP", -no-pie)
-- 
2.34.1