Re: [PATCH] KVM: selftests: x86: Avoid using SSE/AVX instructions

Sean Christopherson
2024-09-22T16:18:09Z

On Fri, Sep 20, 2024, Vitaly Kuznetsov wrote:
> diff --git a/tools/testing/selftests/kvm/Makefile b/tools/testing/selftests/kvm/Makefile
> index 48d32c5aa3eb..3f1b24ed7245 100644
> --- a/tools/testing/selftests/kvm/Makefile
> +++ b/tools/testing/selftests/kvm/Makefile
> @@ -238,6 +238,7 @@ CFLAGS += -Wall -Wstrict-prototypes -Wuninitialized -O2 -g -std=gnu99 \
> -fno-stack-protector -fno-PIE -I$(LINUX_TOOL_INCLUDE) \
> -I$(LINUX_TOOL_ARCH_INCLUDE) -I$(LINUX_HDR_PATH) -Iinclude \
> -I$(<D) -Iinclude/$(ARCH_DIR) -I ../rseq -I.. $(EXTRA_CFLAGS) \
> + -march=x86-64-v2 \

I would rather go straight to playing nice with AVX. Not because I care about
being able to use AVX, but because pretty much every instance where KVM selftests
punts setup to individual tests eventually leads to gross copy+paste code.

The diff ends up being bigger than I was hoping, but that's largely because tests
are already manually enabling stuff in XCR0 (see above copy+paste complaint).

I can post the below later this week (probably as multiple patches).

Note, -march=x86-64-v3 is there just to make it easy to test, I won't actually
include that in the patches :-)

---
tools/testing/selftests/kvm/Makefile | 1 +
.../selftests/kvm/include/x86_64/processor.h | 5 ++++
.../selftests/kvm/lib/x86_64/processor.c | 24 +++++++++++++++++++
tools/testing/selftests/kvm/x86_64/amx_test.c | 23 ++++--------------
.../testing/selftests/kvm/x86_64/cpuid_test.c | 6 ++++-
.../selftests/kvm/x86_64/sev_smoke_test.c | 11 ---------
.../testing/selftests/kvm/x86_64/state_test.c | 5 ----
.../selftests/kvm/x86_64/xcr0_cpuid_test.c | 11 ++++++---
8 files changed, 47 insertions(+), 39 deletions(-)

diff --git a/tools/testing/selftests/kvm/Makefile b/tools/testing/selftests/kvm/Makefile
index 960cf6a77198..7ef4b3cc403d 100644
--- a/tools/testing/selftests/kvm/Makefile
+++ b/tools/testing/selftests/kvm/Makefile
@@ -238,6 +238,7 @@ else
LINUX_TOOL_ARCH_INCLUDE = $(top_srcdir)/tools/arch/$(ARCH)/include
endif
CFLAGS += -Wall -Wstrict-prototypes -Wuninitialized -O2 -g -std=gnu99 \
+ -march=x86-64-v3 \
-Wno-gnu-variable-sized-type-not-at-end -MD -MP -DCONFIG_64BIT \
-fno-builtin-memcmp -fno-builtin-memcpy \
-fno-builtin-memset -fno-builtin-strnlen \
diff --git a/tools/testing/selftests/kvm/include/x86_64/processor.h b/tools/testing/selftests/kvm/include/x86_64/processor.h
index e247f99e0473..645200e95f89 100644
--- a/tools/testing/selftests/kvm/include/x86_64/processor.h
+++ b/tools/testing/selftests/kvm/include/x86_64/processor.h
@@ -1049,6 +1049,11 @@ static inline void vcpu_set_cpuid(struct kvm_vcpu *vcpu)
vcpu_ioctl(vcpu, KVM_GET_CPUID2, vcpu->cpuid);
}

+static inline void vcpu_get_cpuid(struct kvm_vcpu *vcpu)
+{
+ vcpu_ioctl(vcpu, KVM_GET_CPUID2, vcpu->cpuid);
+}
+
void vcpu_set_cpuid_property(struct kvm_vcpu *vcpu,
struct kvm_x86_cpu_property property,
uint32_t value);
diff --git a/tools/testing/selftests/kvm/lib/x86_64/processor.c b/tools/testing/selftests/kvm/lib/x86_64/processor.c
index 974bcd2df6d7..636b29ba8985 100644
--- a/tools/testing/selftests/kvm/lib/x86_64/processor.c
+++ b/tools/testing/selftests/kvm/lib/x86_64/processor.c
@@ -506,6 +506,8 @@ static void vcpu_init_sregs(struct kvm_vm *vm, struct kvm_vcpu *vcpu)

sregs.cr0 = X86_CR0_PE | X86_CR0_NE | X86_CR0_PG;
sregs.cr4 |= X86_CR4_PAE | X86_CR4_OSFXSR;
+ if (kvm_cpu_has(X86_FEATURE_XSAVE))
+ sregs.cr4 |= X86_CR4_OSXSAVE;
sregs.efer |= (EFER_LME | EFER_LMA | EFER_NX);

kvm_seg_set_unusable(&sregs.ldt);
@@ -519,6 +521,20 @@ static void vcpu_init_sregs(struct kvm_vm *vm, struct kvm_vcpu *vcpu)
vcpu_sregs_set(vcpu, &sregs);
}

+static void vcpu_init_xcrs(struct kvm_vm *vm, struct kvm_vcpu *vcpu)
+{
+ struct kvm_xcrs xcrs = {
+ .nr_xcrs = 1,
+ .xcrs[0].xcr = 0,
+ .xcrs[0].value = kvm_cpu_supported_xcr0(),
+ };
+
+ if (!kvm_cpu_has(X86_FEATURE_XSAVE))
+ return;
+
+ vcpu_xcrs_set(vcpu, &xcrs);
+}
+
static void set_idt_entry(struct kvm_vm *vm, int vector, unsigned long addr,
int dpl, unsigned short selector)
{
@@ -675,6 +691,7 @@ struct kvm_vcpu *vm_arch_vcpu_add(struct kvm_vm *vm, uint32_t vcpu_id)
vcpu = __vm_vcpu_add(vm, vcpu_id);
vcpu_init_cpuid(vcpu, kvm_get_supported_cpuid());
vcpu_init_sregs(vm, vcpu);
+ vcpu_init_xcrs(vm, vcpu);

/* Setup guest general purpose registers */
vcpu_regs_get(vcpu, &regs);
@@ -686,6 +703,13 @@ struct kvm_vcpu *vm_arch_vcpu_add(struct kvm_vm *vm, uint32_t vcpu_id)
mp_state.mp_state = 0;
vcpu_mp_state_set(vcpu, &mp_state);

+ /*
+ * Refresh CPUID after setting SREGS and XCR0, so that KVM's "runtime"
+ * updates to guest CPUID, e.g. for OSXSAVE and XSAVE state size, are
+ * reflected into selftests' vCPU CPUID cache, i.e. so that the cache
+ * is consistent with vCPU state.
+ */
+ vcpu_get_cpuid(vcpu);
return vcpu;
}

diff --git a/tools/testing/selftests/kvm/x86_64/amx_test.c b/tools/testing/selftests/kvm/x86_64/amx_test.c
index 903940c54d2d..f4ce5a185a7d 100644
--- a/tools/testing/selftests/kvm/x86_64/amx_test.c
+++ b/tools/testing/selftests/kvm/x86_64/amx_test.c
@@ -86,6 +86,8 @@ static inline void __xsavec(struct xstate *xstate, uint64_t rfbm)

static void check_xtile_info(void)
{
+ GUEST_ASSERT((xgetbv(0) & XFEATURE_MASK_XTILE) == XFEATURE_MASK_XTILE);
+
GUEST_ASSERT(this_cpu_has_p(X86_PROPERTY_XSTATE_MAX_SIZE_XCR0));
GUEST_ASSERT(this_cpu_property(X86_PROPERTY_XSTATE_MAX_SIZE_XCR0) <= XSAVE_SIZE);

@@ -122,29 +124,12 @@ static void set_tilecfg(struct tile_config *cfg)
}
}

-static void init_regs(void)
-{
- uint64_t cr4, xcr0;
-
- GUEST_ASSERT(this_cpu_has(X86_FEATURE_XSAVE));
-
- /* turn on CR4.OSXSAVE */
- cr4 = get_cr4();
- cr4 |= X86_CR4_OSXSAVE;
- set_cr4(cr4);
- GUEST_ASSERT(this_cpu_has(X86_FEATURE_OSXSAVE));
-
- xcr0 = xgetbv(0);
- xcr0 |= XFEATURE_MASK_XTILE;
- xsetbv(0x0, xcr0);
- GUEST_ASSERT((xgetbv(0) & XFEATURE_MASK_XTILE) == XFEATURE_MASK_XTILE);
-}
-
static void __attribute__((__flatten__)) guest_code(struct tile_config *amx_cfg,
struct tile_data *tiledata,
struct xstate *xstate)
{
- init_regs();
+ GUEST_ASSERT(this_cpu_has(X86_FEATURE_XSAVE) &&
+ this_cpu_has(X86_FEATURE_OSXSAVE));
check_xtile_info();
GUEST_SYNC(1);

diff --git a/tools/testing/selftests/kvm/x86_64/cpuid_test.c b/tools/testing/selftests/kvm/x86_64/cpuid_test.c
index 8c579ce714e9..e79a6577254f 100644
--- a/tools/testing/selftests/kvm/x86_64/cpuid_test.c
+++ b/tools/testing/selftests/kvm/x86_64/cpuid_test.c
@@ -37,7 +37,11 @@ static void test_guest_cpuids(struct kvm_cpuid2 *guest_cpuid)

GUEST_ASSERT_EQ(eax, guest_cpuid->entries[i].eax);
GUEST_ASSERT_EQ(ebx, guest_cpuid->entries[i].ebx);
- GUEST_ASSERT_EQ(ecx, guest_cpuid->entries[i].ecx);
+ __GUEST_ASSERT(ecx == guest_cpuid->entries[i].ecx,
+ "CPUID.0x%x.0x%x.ECX 0%x != 0x%x",
+ guest_cpuid->entries[i].function,
+ guest_cpuid->entries[i].index,
+ ecx, guest_cpuid->entries[i].ecx);
GUEST_ASSERT_EQ(edx, guest_cpuid->entries[i].edx);
}

diff --git a/tools/testing/selftests/kvm/x86_64/sev_smoke_test.c b/tools/testing/selftests/kvm/x86_64/sev_smoke_test.c
index 2e9197eb1652..59a5a2227944 100644
--- a/tools/testing/selftests/kvm/x86_64/sev_smoke_test.c
+++ b/tools/testing/selftests/kvm/x86_64/sev_smoke_test.c
@@ -70,12 +70,6 @@ static void test_sync_vmsa(uint32_t policy)

double x87val = M_PI;
struct kvm_xsave __attribute__((aligned(64))) xsave = { 0 };
- struct kvm_sregs sregs;
- struct kvm_xcrs xcrs = {
- .nr_xcrs = 1,
- .xcrs[0].xcr = 0,
- .xcrs[0].value = XFEATURE_MASK_X87_AVX,
- };

vm = vm_sev_create_with_one_vcpu(KVM_X86_SEV_ES_VM, guest_code_xsave, &vcpu);
gva = vm_vaddr_alloc_shared(vm, PAGE_SIZE, KVM_UTIL_MIN_VADDR,
@@ -84,11 +78,6 @@ static void test_sync_vmsa(uint32_t policy)

vcpu_args_set(vcpu, 1, gva);

- vcpu_sregs_get(vcpu, &sregs);
- sregs.cr4 |= X86_CR4_OSFXSR | X86_CR4_OSXSAVE;
- vcpu_sregs_set(vcpu, &sregs);
-
- vcpu_xcrs_set(vcpu, &xcrs);
asm("fninit\n"
"vpcmpeqb %%ymm4, %%ymm4, %%ymm4\n"
"fldl %3\n"
diff --git a/tools/testing/selftests/kvm/x86_64/state_test.c b/tools/testing/selftests/kvm/x86_64/state_test.c
index 1c756db329e5..141b7fc0c965 100644
--- a/tools/testing/selftests/kvm/x86_64/state_test.c
+++ b/tools/testing/selftests/kvm/x86_64/state_test.c
@@ -145,11 +145,6 @@ static void __attribute__((__flatten__)) guest_code(void *arg)

memset(buffer, 0xcc, sizeof(buffer));

- set_cr4(get_cr4() | X86_CR4_OSXSAVE);
- GUEST_ASSERT(this_cpu_has(X86_FEATURE_OSXSAVE));
-
- xsetbv(0, xgetbv(0) | supported_xcr0);
-
/*
* Modify state for all supported xfeatures to take them out of
* their "init" state, i.e. to make them show up in XSTATE_BV.
diff --git a/tools/testing/selftests/kvm/x86_64/xcr0_cpuid_test.c b/tools/testing/selftests/kvm/x86_64/xcr0_cpuid_test.c
index 95ce192d0753..c8a5c5e51661 100644
--- a/tools/testing/selftests/kvm/x86_64/xcr0_cpuid_test.c
+++ b/tools/testing/selftests/kvm/x86_64/xcr0_cpuid_test.c
@@ -48,16 +48,16 @@ do { \

static void guest_code(void)
{
- uint64_t xcr0_reset;
+ uint64_t initial_xcr0;
uint64_t supported_xcr0;
int i, vector;

set_cr4(get_cr4() | X86_CR4_OSXSAVE);

- xcr0_reset = xgetbv(0);
+ initial_xcr0 = xgetbv(0);
supported_xcr0 = this_cpu_supported_xcr0();

- GUEST_ASSERT(xcr0_reset == XFEATURE_MASK_FP);
+ GUEST_ASSERT(initial_xcr0 == supported_xcr0);

/* Check AVX */
ASSERT_XFEATURE_DEPENDENCIES(supported_xcr0,
@@ -79,6 +79,11 @@ static void guest_code(void)
ASSERT_ALL_OR_NONE_XFEATURE(supported_xcr0,
XFEATURE_MASK_XTILE);

+ vector = xsetbv_safe(0, XFEATURE_MASK_FP);
+ __GUEST_ASSERT(!vector,
+ "Expected success on XSETBV(FP), got vector '0x%x'",
+ vector);
+
vector = xsetbv_safe(0, supported_xcr0);
__GUEST_ASSERT(!vector,
"Expected success on XSETBV(0x%lx), got vector '0x%x'",

base-commit: 3f8df6285271d9d8f17d733433e5213a63b83a0b
--