[PATCH v2 0/4] KVM: selftests: AMX test fix and cleanups

[PATCH v2 0/4] KVM: selftests: AMX test fix and cleanups

[Sean Christopherson]

Fix a bug in the AMX test introduced by moving to kvm_cpu_has() for
X86_FEATURE_XFD, and clean up the related code.  The fix and cleanups
all revolve around ARCH_REQ_XCOMP_GUEST_PERM impacting the output of
KVM_GET_SUPPORTED_CPUID, and thus causing problems for selftest's
caching of KVM's supported CPUID.

Lei Wang, I adjusted your Author and SOB tags to drop the comma, which I
think? violates that "use your real name" rule, and use formatting from
patches you've sent in the past[*].  Let me know if that's ok (or not).

[*] https://lore.kernel.org/all/20220424101557.134102-9-lei4.wang@intel.com

Lei Wang (1):
  KVM: selftests: Move XFD CPUID checking out of
    __vm_xsave_require_permission()

Sean Christopherson (3):
  KVM: selftests: Move __vm_xsave_require_permission() below CPUID
    helpers
  KVM: selftests: Disallow "get supported CPUID" before
    REQ_XCOMP_GUEST_PERM
  KVM: selftests: Do kvm_cpu_has() checks before creating VM+vCPU

 .../selftests/kvm/lib/x86_64/processor.c      | 84 ++++++++++---------
 tools/testing/selftests/kvm/x86_64/amx_test.c | 11 ++-
 2 files changed, 52 insertions(+), 43 deletions(-)


base-commit: 519c2002cd92bdc37c8412ca22cb9c7e7bc48c48
-- 
2.38.1.584.g0f3c55d4c2-goog

[PATCH v2 1/4] KVM: selftests: Move XFD CPUID checking out of __vm_xsave_require_permission()

[Sean Christopherson]

From: Lei Wang <lei4.wang@intel.com>

Move the kvm_cpu_has() check on X86_FEATURE_XFD out of the helper to
enable off-by-default XSAVE-managed features and into the one test that
currenty requires XFD (XFeature Disable) support.   kvm_cpu_has() uses
kvm_get_supported_cpuid() and thus caches KVM_GET_SUPPORTED_CPUID, and so
using kvm_cpu_has() before ARCH_REQ_XCOMP_GUEST_PERM effectively results
in the test caching stale values, e.g. subsequent checks on AMX_TILE will
get false negatives.

Although off-by-default features are nonsensical without XFD, checking
for XFD virtualization prior to enabling such features isn't strictly
required.

Signed-off-by: Lei Wang <lei4.wang@intel.com>
Fixes: 7fbb653e01fd ("KVM: selftests: Check KVM's supported CPUID, not host CPUID, for XFD")
Link: https://lore.kernel.org/r/20221125023839.315207-1-lei4.wang@intel.com
[sean: add Fixes, reword changelog]
Signed-off-by: Sean Christopherson <seanjc@google.com>
---
 tools/testing/selftests/kvm/lib/x86_64/processor.c | 2 --
 tools/testing/selftests/kvm/x86_64/amx_test.c      | 1 +
 2 files changed, 1 insertion(+), 2 deletions(-)

diff --git a/tools/testing/selftests/kvm/lib/x86_64/processor.c b/tools/testing/selftests/kvm/lib/x86_64/processor.c
index d532c20c74fd..aac7b32a794b 100644
--- a/tools/testing/selftests/kvm/lib/x86_64/processor.c
+++ b/tools/testing/selftests/kvm/lib/x86_64/processor.c
@@ -563,8 +563,6 @@ void __vm_xsave_require_permission(int bit, const char *name)
 		.addr = (unsigned long) &bitmask
 	};
 
-	TEST_REQUIRE(kvm_cpu_has(X86_FEATURE_XFD));
-
 	kvm_fd = open_kvm_dev_path_or_exit();
 	rc = __kvm_ioctl(kvm_fd, KVM_GET_DEVICE_ATTR, &attr);
 	close(kvm_fd);
diff --git a/tools/testing/selftests/kvm/x86_64/amx_test.c b/tools/testing/selftests/kvm/x86_64/amx_test.c
index 21de6ae42086..1256c7faadd3 100644
--- a/tools/testing/selftests/kvm/x86_64/amx_test.c
+++ b/tools/testing/selftests/kvm/x86_64/amx_test.c
@@ -254,6 +254,7 @@ int main(int argc, char *argv[])
 	/* Create VM */
 	vm = vm_create_with_one_vcpu(&vcpu, guest_code);
 
+	TEST_REQUIRE(kvm_cpu_has(X86_FEATURE_XFD));
 	TEST_REQUIRE(kvm_cpu_has(X86_FEATURE_XSAVE));
 	TEST_REQUIRE(kvm_cpu_has(X86_FEATURE_AMX_TILE));
 	TEST_REQUIRE(kvm_cpu_has(X86_FEATURE_XTILECFG));
-- 
2.38.1.584.g0f3c55d4c2-goog

[PATCH v2 2/4] KVM: selftests: Move __vm_xsave_require_permission() below CPUID helpers

[Sean Christopherson]

Move __vm_xsave_require_permission() below the CPUID helpers so that a
future change can reference the cached result of KVM_GET_SUPPORTED_CPUID
while keeping the definition of the variable close to its intended user,
kvm_get_supported_cpuid().

No functional change intended.

Signed-off-by: Sean Christopherson <seanjc@google.com>
---
 .../selftests/kvm/lib/x86_64/processor.c      | 64 +++++++++----------
 1 file changed, 32 insertions(+), 32 deletions(-)

diff --git a/tools/testing/selftests/kvm/lib/x86_64/processor.c b/tools/testing/selftests/kvm/lib/x86_64/processor.c
index aac7b32a794b..23067465c035 100644
--- a/tools/testing/selftests/kvm/lib/x86_64/processor.c
+++ b/tools/testing/selftests/kvm/lib/x86_64/processor.c
@@ -552,38 +552,6 @@ static void vcpu_setup(struct kvm_vm *vm, struct kvm_vcpu *vcpu)
 	vcpu_sregs_set(vcpu, &sregs);
 }
 
-void __vm_xsave_require_permission(int bit, const char *name)
-{
-	int kvm_fd;
-	u64 bitmask;
-	long rc;
-	struct kvm_device_attr attr = {
-		.group = 0,
-		.attr = KVM_X86_XCOMP_GUEST_SUPP,
-		.addr = (unsigned long) &bitmask
-	};
-
-	kvm_fd = open_kvm_dev_path_or_exit();
-	rc = __kvm_ioctl(kvm_fd, KVM_GET_DEVICE_ATTR, &attr);
-	close(kvm_fd);
-
-	if (rc == -1 && (errno == ENXIO || errno == EINVAL))
-		__TEST_REQUIRE(0, "KVM_X86_XCOMP_GUEST_SUPP not supported");
-
-	TEST_ASSERT(rc == 0, "KVM_GET_DEVICE_ATTR(0, KVM_X86_XCOMP_GUEST_SUPP) error: %ld", rc);
-
-	__TEST_REQUIRE(bitmask & (1ULL << bit),
-		       "Required XSAVE feature '%s' not supported", name);
-
-	TEST_REQUIRE(!syscall(SYS_arch_prctl, ARCH_REQ_XCOMP_GUEST_PERM, bit));
-
-	rc = syscall(SYS_arch_prctl, ARCH_GET_XCOMP_GUEST_PERM, &bitmask);
-	TEST_ASSERT(rc == 0, "prctl(ARCH_GET_XCOMP_GUEST_PERM) error: %ld", rc);
-	TEST_ASSERT(bitmask & (1ULL << bit),
-		    "prctl(ARCH_REQ_XCOMP_GUEST_PERM) failure bitmask=0x%lx",
-		    bitmask);
-}
-
 void kvm_arch_vm_post_create(struct kvm_vm *vm)
 {
 	vm_create_irqchip(vm);
@@ -705,6 +673,38 @@ uint64_t kvm_get_feature_msr(uint64_t msr_index)
 	return buffer.entry.data;
 }
 
+void __vm_xsave_require_permission(int bit, const char *name)
+{
+	int kvm_fd;
+	u64 bitmask;
+	long rc;
+	struct kvm_device_attr attr = {
+		.group = 0,
+		.attr = KVM_X86_XCOMP_GUEST_SUPP,
+		.addr = (unsigned long) &bitmask
+	};
+
+	kvm_fd = open_kvm_dev_path_or_exit();
+	rc = __kvm_ioctl(kvm_fd, KVM_GET_DEVICE_ATTR, &attr);
+	close(kvm_fd);
+
+	if (rc == -1 && (errno == ENXIO || errno == EINVAL))
+		__TEST_REQUIRE(0, "KVM_X86_XCOMP_GUEST_SUPP not supported");
+
+	TEST_ASSERT(rc == 0, "KVM_GET_DEVICE_ATTR(0, KVM_X86_XCOMP_GUEST_SUPP) error: %ld", rc);
+
+	__TEST_REQUIRE(bitmask & (1ULL << bit),
+		       "Required XSAVE feature '%s' not supported", name);
+
+	TEST_REQUIRE(!syscall(SYS_arch_prctl, ARCH_REQ_XCOMP_GUEST_PERM, bit));
+
+	rc = syscall(SYS_arch_prctl, ARCH_GET_XCOMP_GUEST_PERM, &bitmask);
+	TEST_ASSERT(rc == 0, "prctl(ARCH_GET_XCOMP_GUEST_PERM) error: %ld", rc);
+	TEST_ASSERT(bitmask & (1ULL << bit),
+		    "prctl(ARCH_REQ_XCOMP_GUEST_PERM) failure bitmask=0x%lx",
+		    bitmask);
+}
+
 void vcpu_init_cpuid(struct kvm_vcpu *vcpu, const struct kvm_cpuid2 *cpuid)
 {
 	TEST_ASSERT(cpuid != vcpu->cpuid, "@cpuid can't be the vCPU's CPUID");
-- 
2.38.1.584.g0f3c55d4c2-goog

[PATCH v2 3/4] KVM: selftests: Disallow "get supported CPUID" before REQ_XCOMP_GUEST_PERM

[Sean Christopherson]

Disallow using kvm_get_supported_cpuid() and thus caching KVM's supported
CPUID info before enabling XSAVE-managed features that are off-by-default
and must be enabled by ARCH_REQ_XCOMP_GUEST_PERM.  Caching the supported
CPUID before all XSAVE features are enabled can result in false negatives
due to testing features that were cached before they were enabled.

Signed-off-by: Sean Christopherson <seanjc@google.com>
---
 .../selftests/kvm/lib/x86_64/processor.c       | 18 ++++++++++++------
 1 file changed, 12 insertions(+), 6 deletions(-)

diff --git a/tools/testing/selftests/kvm/lib/x86_64/processor.c b/tools/testing/selftests/kvm/lib/x86_64/processor.c
index 23067465c035..1d3829e652e6 100644
--- a/tools/testing/selftests/kvm/lib/x86_64/processor.c
+++ b/tools/testing/selftests/kvm/lib/x86_64/processor.c
@@ -601,21 +601,24 @@ void vcpu_arch_free(struct kvm_vcpu *vcpu)
 		free(vcpu->cpuid);
 }
 
+/* Do not use kvm_supported_cpuid directly except for validity checks. */
+static void *kvm_supported_cpuid;
+
 const struct kvm_cpuid2 *kvm_get_supported_cpuid(void)
 {
-	static struct kvm_cpuid2 *cpuid;
 	int kvm_fd;
 
-	if (cpuid)
-		return cpuid;
+	if (kvm_supported_cpuid)
+		return kvm_supported_cpuid;
 
-	cpuid = allocate_kvm_cpuid2(MAX_NR_CPUID_ENTRIES);
+	kvm_supported_cpuid = allocate_kvm_cpuid2(MAX_NR_CPUID_ENTRIES);
 	kvm_fd = open_kvm_dev_path_or_exit();
 
-	kvm_ioctl(kvm_fd, KVM_GET_SUPPORTED_CPUID, cpuid);
+	kvm_ioctl(kvm_fd, KVM_GET_SUPPORTED_CPUID,
+		  (struct kvm_cpuid2 *)kvm_supported_cpuid);
 
 	close(kvm_fd);
-	return cpuid;
+	return kvm_supported_cpuid;
 }
 
 static uint32_t __kvm_cpu_has(const struct kvm_cpuid2 *cpuid,
@@ -684,6 +687,9 @@ void __vm_xsave_require_permission(int bit, const char *name)
 		.addr = (unsigned long) &bitmask
 	};
 
+	TEST_ASSERT(!kvm_supported_cpuid,
+		    "kvm_get_supported_cpuid() cannot be used before ARCH_REQ_XCOMP_GUEST_PERM");
+
 	kvm_fd = open_kvm_dev_path_or_exit();
 	rc = __kvm_ioctl(kvm_fd, KVM_GET_DEVICE_ATTR, &attr);
 	close(kvm_fd);
-- 
2.38.1.584.g0f3c55d4c2-goog

[PATCH v2 4/4] KVM: selftests: Do kvm_cpu_has() checks before creating VM+vCPU

[Sean Christopherson]

Move the AMX test's kvm_cpu_has() checks before creating the VM+vCPU,
there are no dependencies between the two operations.  Opportunistically
add a comment to call out that enabling off-by-default XSAVE-managed
features must be done before KVM_GET_SUPPORTED_CPUID is cached.

Signed-off-by: Sean Christopherson <seanjc@google.com>
---
 tools/testing/selftests/kvm/x86_64/amx_test.c | 10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

diff --git a/tools/testing/selftests/kvm/x86_64/amx_test.c b/tools/testing/selftests/kvm/x86_64/amx_test.c
index 1256c7faadd3..bd72c6eb3b67 100644
--- a/tools/testing/selftests/kvm/x86_64/amx_test.c
+++ b/tools/testing/selftests/kvm/x86_64/amx_test.c
@@ -249,17 +249,21 @@ int main(int argc, char *argv[])
 	u32 amx_offset;
 	int stage, ret;
 
+	/*
+	 * Note, all off-by-default features must be enabled before anything
+	 * caches KVM_GET_SUPPORTED_CPUID, e.g. before using kvm_cpu_has().
+	 */
 	vm_xsave_require_permission(XSTATE_XTILE_DATA_BIT);
 
-	/* Create VM */
-	vm = vm_create_with_one_vcpu(&vcpu, guest_code);
-
 	TEST_REQUIRE(kvm_cpu_has(X86_FEATURE_XFD));
 	TEST_REQUIRE(kvm_cpu_has(X86_FEATURE_XSAVE));
 	TEST_REQUIRE(kvm_cpu_has(X86_FEATURE_AMX_TILE));
 	TEST_REQUIRE(kvm_cpu_has(X86_FEATURE_XTILECFG));
 	TEST_REQUIRE(kvm_cpu_has(X86_FEATURE_XTILEDATA));
 
+	/* Create VM */
+	vm = vm_create_with_one_vcpu(&vcpu, guest_code);
+
 	TEST_ASSERT(kvm_cpu_has_p(X86_PROPERTY_XSTATE_MAX_SIZE),
 		    "KVM should enumerate max XSAVE size when XSAVE is supported");
 	xsave_restore_size = kvm_cpu_property(X86_PROPERTY_XSTATE_MAX_SIZE);
-- 
2.38.1.584.g0f3c55d4c2-goog

Re: [PATCH v2 0/4] KVM: selftests: AMX test fix and cleanups

[Wang, Lei]

On 11/29/2022 6:57 AM, Sean Christopherson wrote:
> Fix a bug in the AMX test introduced by moving to kvm_cpu_has() for
> X86_FEATURE_XFD, and clean up the related code.  The fix and cleanups
> all revolve around ARCH_REQ_XCOMP_GUEST_PERM impacting the output of
> KVM_GET_SUPPORTED_CPUID, and thus causing problems for selftest's
> caching of KVM's supported CPUID.
> 
> Lei Wang, I adjusted your Author and SOB tags to drop the comma, which I
> think? violates that "use your real name" rule, and use formatting from
> patches you've sent in the past[*].  Let me know if that's ok (or not).

That's OK, thanks!

> [*] https://lore.kernel.org/all/20220424101557.134102-9-lei4.wang@intel.com
> 
> Lei Wang (1):
>   KVM: selftests: Move XFD CPUID checking out of
>     __vm_xsave_require_permission()
> 
> Sean Christopherson (3):
>   KVM: selftests: Move __vm_xsave_require_permission() below CPUID
>     helpers
>   KVM: selftests: Disallow "get supported CPUID" before
>     REQ_XCOMP_GUEST_PERM
>   KVM: selftests: Do kvm_cpu_has() checks before creating VM+vCPU
> 
>  .../selftests/kvm/lib/x86_64/processor.c      | 84 ++++++++++---------
>  tools/testing/selftests/kvm/x86_64/amx_test.c | 11 ++-
>  2 files changed, 52 insertions(+), 43 deletions(-)
> 
> 
> base-commit: 519c2002cd92bdc37c8412ca22cb9c7e7bc48c48