linux-kernel - [PATCH 4/5] selftests, kvm: try getting XFD and XSAVE state out of sync

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Message-ID: <20251224001249.1041934-5-pbonzini@redhat.com>
Date: Wed, 24 Dec 2025 01:12:48 +0100
From: Paolo Bonzini <pbonzini@...hat.com>
To: linux-kernel@...r.kernel.org,
	kvm@...r.kernel.org
Cc: seanjc@...gle.com,
	x86@...nel.org
Subject: [PATCH 4/5] selftests, kvm: try getting XFD and XSAVE state out of sync

The host is allowed to set FPU state that includes a disabled
xstate component.  Check that this does not cause bad effects.

Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
---
 tools/testing/selftests/kvm/x86/amx_test.c | 25 +++++++++++++++++++---
 1 file changed, 22 insertions(+), 3 deletions(-)

diff --git a/tools/testing/selftests/kvm/x86/amx_test.c b/tools/testing/selftests/kvm/x86/amx_test.c
index dd980cdac5df..5222ec6f71d3 100644
--- a/tools/testing/selftests/kvm/x86/amx_test.c
+++ b/tools/testing/selftests/kvm/x86/amx_test.c
@@ -142,7 +142,16 @@ static void __attribute__((__flatten__)) guest_code(struct tile_config *amx_cfg,
 	GUEST_SYNC(3);
 	/* Check save/restore when trap to userspace */
 	__tileloadd(tiledata);
+
 	GUEST_SYNC(4);
+	/* xfd=0x40000, disable amx tiledata */
+	wrmsr(MSR_IA32_XFD, XFEATURE_MASK_XTILE_DATA);
+
+	GUEST_SYNC(5);
+	/* host tries setting tiledata while guest XFD is set */
+	GUEST_SYNC(6);
+
+	wrmsr(MSR_IA32_XFD, 0);
 	__tilerelease();
 	GUEST_SYNC(10);
 	/*
@@ -202,6 +211,7 @@ int main(int argc, char *argv[])
 	struct kvm_vcpu *vcpu;
 	struct kvm_vm *vm;
 	struct kvm_x86_state *state;
+	struct kvm_x86_state *tile_state = NULL;
 	int xsave_restore_size;
 	vm_vaddr_t amx_cfg, tiledata, xstate;
 	struct ucall uc;
@@ -259,6 +269,7 @@ int main(int argc, char *argv[])
 			case 1:
 			case 2:
 			case 3:
+			case 6:
 			case 10:
 			case 11:
 			case 12:
@@ -267,8 +278,7 @@ int main(int argc, char *argv[])
 				break;
 			case 4:
 			case 15:
-				fprintf(stderr,
-				"GUEST_SYNC(%ld), check save/restore status\n", uc.args[1]);
+				fprintf(stderr, "GUEST_SYNC(%ld), check save/restore status\n", uc.args[1]);
 
 				/* Compacted mode, get amx offset by xsave area
 				 * size subtract 8K amx size.
@@ -280,8 +290,17 @@ int main(int argc, char *argv[])
 				/* Only check TMM0 register, 1 tile */
 				ret = memcmp(amx_start, tiles_data, TILE_SIZE);
 				TEST_ASSERT(ret == 0, "memcmp failed, ret=%d", ret);
-				kvm_x86_state_cleanup(state);
+				if (uc.args[1] == 4)
+					tile_state = state;
+				else
+					kvm_x86_state_cleanup(state);
 				break;
+			case 5:
+				fprintf(stderr, "GUEST_SYNC(%ld), before KVM_SET_XSAVE\n", uc.args[1]);
+				vcpu_xsave_set(vcpu, tile_state->xsave);
+				fprintf(stderr, "GUEST_SYNC(%ld), after KVM_SET_XSAVE\n", uc.args[1]);
+				/* do not restore full state */
+				continue;
 			case 14:
 				fprintf(stderr,
 				"GUEST_SYNC(%ld), #NM exception and enable amx\n", uc.args[1]);
-- 
2.52.0