[PATCH 3/4] KVM: selftests: x86: Enable checking on xcomp_bv in amx_test

[Mingwei Zhang]

After tilerelease instruction, AMX tiles are in INIT state. According to
Intel SDM vol 1. 13.10: "If RFBM[i] = 1, XSTATE_BV[i] is set to the
value of XINUSE[i].", XSTATE_BV[18] should be cleared after xsavec.

On the other hand, according to Intel SDM vol 1. 13.4.3: "If XCOMP_BV[i] =
1, state component i is located at a byte offset locationI from the base
address of the XSAVE area". Since at the time of xsavec, XCR0[18] is set
indicating AMX tile data component is still enabled, xcomp_bv[18] should be
set.

Complete the checks by adding the assert to xcomp_bv[18] after xsavec.

Signed-off-by: Mingwei Zhang <mizhang@xxxxxxxxxx>
---
 tools/testing/selftests/kvm/x86_64/amx_test.c | 30 +++++++++++++++++--
 1 file changed, 27 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 b2369f956fea..18203e399e9d 100644
--- a/tools/testing/selftests/kvm/x86_64/amx_test.c
+++ b/tools/testing/selftests/kvm/x86_64/amx_test.c
@@ -41,6 +41,12 @@
 
 #define XSAVE_HDR_OFFSET		512
 
+struct xstate_header {
+	u64	xfeatures;
+	u64	xcomp_bv;
+	u64	reserved[6];
+} __packed;
+
 struct xsave_data {
 	u8 area[XSAVE_SIZE];
 } __aligned(64);
@@ -160,12 +166,26 @@ static void set_tilecfg(struct tile_config *cfg)
 
 static void set_xstatebv(void *data, uint64_t bv)
 {
-	*(uint64_t *)(data + XSAVE_HDR_OFFSET) = bv;
+	struct xstate_header *header =
+		(struct xstate_header *)(data + XSAVE_HDR_OFFSET);
+
+	header->xfeatures = bv;
 }
 
 static u64 get_xstatebv(void *data)
 {
-	return *(u64 *)(data + XSAVE_HDR_OFFSET);
+	struct xstate_header *header =
+		(struct xstate_header *)(data + XSAVE_HDR_OFFSET);
+
+	return header->xfeatures;
+}
+
+static u64 get_xcompbv(void *data)
+{
+	struct xstate_header *header =
+		(struct xstate_header *)(data + XSAVE_HDR_OFFSET);
+
+	return header->xcomp_bv;
 }
 
 static void init_regs(void)
@@ -204,10 +224,14 @@ static void __attribute__((__flatten__)) guest_code(struct tile_config *amx_cfg,
 	GUEST_SYNC(4);
 	__tilerelease();
 	GUEST_SYNC(5);
-	/* bit 18 not in the XSTATE_BV after xsavec() */
+	/*
+	 * After xsavec() bit 18 is cleared in the XSTATE_BV but is set in
+	 * the XCOMP_BV.
+	 */
 	set_xstatebv(xsave_data, XFEATURE_MASK_XTILEDATA);
 	__xsavec(xsave_data, XFEATURE_MASK_XTILEDATA);
 	GUEST_ASSERT((get_xstatebv(xsave_data) & XFEATURE_MASK_XTILEDATA) == 0);
+	GUEST_ASSERT((get_xcompbv(xsave_data) & XFEATURE_MASK_XTILEDATA) == XFEATURE_MASK_XTILEDATA);
 
 	/* xfd=0x40000, disable amx tiledata */
 	wrmsr(MSR_IA32_XFD, XFEATURE_MASK_XTILEDATA);
-- 
2.39.0.314.g84b9a713c41-goog