selftests/mm: fix cross compilation with LLVM

Currently the MM selftests attempt to work out the target architecture by
using CROSS_COMPILE or otherwise querying the host machine, storing the
target architecture in a variable called MACHINE rather than the usual
ARCH though as far as I can tell (including for x86_64) the value is the
same as we would use for architecture.

When cross compiling with LLVM we don't need a CROSS_COMPILE as LLVM can
support many target architectures in a single build so this logic does not
work, CROSS_COMPILE is not set and we end up selecting tests for the host
rather than target architecture.  Fix this by using the more standard ARCH
to describe the architecture, taking it from the environment if specified.

Link: https://lkml.kernel.org/r/20230614-kselftest-mm-llvm-v1-1-180523f277d3@kernel.orgSigned-off-by: Mark Brown <broonie@kernel.org>
Cc: Nick Desaulniers <ndesaulniers@google.com>
Cc: Albert Ou <aou@eecs.berkeley.edu>
Cc: Nathan Chancellor <nathan@kernel.org>
Cc: Nick Desaulniers <ndesaulniers@google.com>
Cc: Palmer Dabbelt <palmer@dabbelt.com>
Cc: Paul Walmsley <paul.walmsley@sifive.com>
Cc: Shuah Khan <shuah@kernel.org>
Cc: Tom Rix <trix@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

tools/testing/selftests/mm/Makefile

@@ -5,12 +5,15 @@ LOCAL_HDRS += $(selfdir)/mm/local_config.h $(top_srcdir)/mm/gup_test.h
 
 include local_config.mk
 
+ifeq ($(ARCH),)
+
 ifeq ($(CROSS_COMPILE),)
 uname_M := $(shell uname -m 2>/dev/null || echo not)
 else
 uname_M := $(shell echo $(CROSS_COMPILE) | grep -o '^[a-z0-9]\+')
 endif
-MACHINE ?= $(shell echo $(uname_M) | sed -e 's/aarch64.*/arm64/' -e 's/ppc64.*/ppc64/')
+ARCH ?= $(shell echo $(uname_M) | sed -e 's/aarch64.*/arm64/' -e 's/ppc64.*/ppc64/')
+endif
 
 # Without this, failed build products remain, with up-to-date timestamps,
 # thus tricking Make (and you!) into believing that All Is Well, in subsequent
@@ -65,7 +68,7 @@ TEST_GEN_PROGS += ksm_tests
 TEST_GEN_PROGS += ksm_functional_tests
 TEST_GEN_PROGS += mdwe_test
 
-ifeq ($(MACHINE),x86_64)
+ifeq ($(ARCH),x86_64)
 CAN_BUILD_I386 := $(shell ./../x86/check_cc.sh "$(CC)" ../x86/trivial_32bit_program.c -m32)
 CAN_BUILD_X86_64 := $(shell ./../x86/check_cc.sh "$(CC)" ../x86/trivial_64bit_program.c)
 CAN_BUILD_WITH_NOPIE := $(shell ./../x86/check_cc.sh "$(CC)" ../x86/trivial_program.c -no-pie)
@@ -87,13 +90,13 @@ TEST_GEN_PROGS += $(BINARIES_64)
 endif
 else
 
-ifneq (,$(findstring $(MACHINE),ppc64))
+ifneq (,$(findstring $(ARCH),ppc64))
 TEST_GEN_PROGS += protection_keys
 endif
 
 endif
 
-ifneq (,$(filter $(MACHINE),arm64 ia64 mips64 parisc64 ppc64 riscv64 s390x sparc64 x86_64))
+ifneq (,$(filter $(ARCH),arm64 ia64 mips64 parisc64 ppc64 riscv64 s390x sparc64 x86_64))
 TEST_GEN_PROGS += va_high_addr_switch
 TEST_GEN_PROGS += virtual_address_range
 TEST_GEN_PROGS += write_to_hugetlbfs
@@ -112,7 +115,7 @@ $(TEST_GEN_PROGS): vm_util.c
 $(OUTPUT)/uffd-stress: uffd-common.c
 $(OUTPUT)/uffd-unit-tests: uffd-common.c
 
-ifeq ($(MACHINE),x86_64)
+ifeq ($(ARCH),x86_64)
 BINARIES_32 := $(patsubst %,$(OUTPUT)/%,$(BINARIES_32))
 BINARIES_64 := $(patsubst %,$(OUTPUT)/%,$(BINARIES_64))