linux-kernel - [PATCH RFC 5/7] kvm: x86: Revise CPUID.D.1.EBX for alignment rule

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Message-Id: <20210207154256.52850-6-jing2.liu@linux.intel.com>
Date:   Sun,  7 Feb 2021 10:42:54 -0500
From:   Jing Liu <jing2.liu@...ux.intel.com>
To:     pbonzini@...hat.com, seanjc@...gle.com, kvm@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org, jing2.liu@...el.com
Subject: [PATCH RFC 5/7] kvm: x86: Revise CPUID.D.1.EBX for alignment rule

CPUID.0xD.1.EBX[1] is set if, when the compacted format of an XSAVE
area is used, this extended state component located on the next
64-byte boundary following the preceding state component (otherwise,
it is located immediately following the preceding state component).

AMX tileconfig and tiledata are the first to use 64B alignment.
Revise the runtime cpuid modification for this rule.

Signed-off-by: Jing Liu <jing2.liu@...ux.intel.com>
---
 arch/x86/kvm/cpuid.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
index 04a73c395c71..ee1fac0a865e 100644
--- a/arch/x86/kvm/cpuid.c
+++ b/arch/x86/kvm/cpuid.c
@@ -35,12 +35,17 @@ static u32 xstate_required_size(u64 xstate_bv, bool compacted)
 {
 	int feature_bit = 0;
 	u32 ret = XSAVE_HDR_SIZE + XSAVE_HDR_OFFSET;
+	bool is_aligned = false;
 
 	xstate_bv &= XFEATURE_MASK_EXTEND;
 	while (xstate_bv) {
 		if (xstate_bv & 0x1) {
 		        u32 eax, ebx, ecx, edx, offset;
 		        cpuid_count(0xD, feature_bit, &eax, &ebx, &ecx, &edx);
+			/* ECX[2]: 64B alignment in compacted form */
+			is_aligned = !!(ecx & 2);
+			if (is_aligned && compacted)
+				ret = ALIGN(ret, 64);
 			offset = compacted ? ret : ebx;
 			ret = max(ret, offset + eax);
 		}
-- 
2.18.4