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From: Paolo Bonzini <pbonzini@redhat.com>
To: linux-kernel@vger.kernel.org, kvm@vger.kernel.org
Cc: kbusch@kernel.org, chang.seok.bae@intel.com
Subject: [PATCH 02/10] KVM: emulate: move Src2Shift up one bit
Date: Thu, 13 Nov 2025 19:36:25 -0500	[thread overview]
Message-ID: <20251114003633.60689-3-pbonzini@redhat.com> (raw)
In-Reply-To: <20251114003633.60689-1-pbonzini@redhat.com>

An irresistible microoptimization (changing accesses to Src2 to just an
AND :)) that also frees a bit for AVX in the low flags word.  This makes
it closer to SSE since both of them can access XMM registers, pointlessly
shaving another clock cycle or two (maybe).

No functional change intended.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
 arch/x86/kvm/emulate.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c
index 43ae4fcb2137..57799b5d9da2 100644
--- a/arch/x86/kvm/emulate.c
+++ b/arch/x86/kvm/emulate.c
@@ -147,7 +147,7 @@
 #define PageTable   (1 << 29)   /* instruction used to write page table */
 #define NotImpl     (1 << 30)   /* instruction is not implemented */
 /* Source 2 operand type */
-#define Src2Shift   (31)
+#define Src2Shift   (32)       /* bits 32-36 */
 #define Src2None    (OpNone << Src2Shift)
 #define Src2Mem     (OpMem << Src2Shift)
 #define Src2CL      (OpCL << Src2Shift)
@@ -161,6 +161,7 @@
 #define Src2FS      (OpFS << Src2Shift)
 #define Src2GS      (OpGS << Src2Shift)
 #define Src2Mask    (OpMask << Src2Shift)
+/* free: 37-39 */
 #define Mmx         ((u64)1 << 40)  /* MMX Vector instruction */
 #define AlignMask   ((u64)7 << 41)
 #define Aligned     ((u64)1 << 41)  /* Explicitly aligned (e.g. MOVDQA) */
-- 
2.43.5



  parent reply	other threads:[~2025-11-14  0:36 UTC|newest]

Thread overview: 22+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2025-11-14  0:36 [PATCH 00/10] KVM: emulate: enable AVX moves Paolo Bonzini
2025-11-14  0:36 ` [PATCH 01/10] KVM: emulate: add MOVNTDQA Paolo Bonzini
2025-11-14  0:36 ` Paolo Bonzini [this message]
2025-11-17 19:51   ` [PATCH 02/10] KVM: emulate: move Src2Shift up one bit Chang S. Bae
2025-11-14  0:36 ` [PATCH 03/10] KVM: emulate: improve formatting of flags table Paolo Bonzini
2025-11-17 19:53   ` Chang S. Bae
2025-11-14  0:36 ` [PATCH 04/10] KVM: emulate: move op_prefix to struct x86_emulate_ctxt Paolo Bonzini
2025-11-17 19:54   ` Chang S. Bae
2025-11-14  0:36 ` [PATCH 05/10] KVM: emulate: share common register decoding code Paolo Bonzini
2025-11-17 19:55   ` Chang S. Bae
2025-11-14  0:36 ` [PATCH 06/10] KVM: emulate: add get_xcr callback Paolo Bonzini
2025-11-17 19:56   ` Chang S. Bae
2025-11-14  0:36 ` [PATCH 07/10] KVM: emulate: add AVX support to register fetch and writeback Paolo Bonzini
2025-11-14 17:06   ` kernel test robot
2025-11-14 20:10   ` kernel test robot
2025-11-14  0:36 ` [PATCH 08/10] KVM: x86: Refactor REX prefix handling in instruction emulation Paolo Bonzini
2025-11-17 19:56   ` Chang S. Bae
2025-11-14  0:36 ` [PATCH 09/10] KVM: emulate: decode VEX prefix Paolo Bonzini
2025-11-14  0:36 ` [PATCH 10/10] KVM: emulate: enable AVX moves Paolo Bonzini
2025-11-14  0:51 ` [PATCH 00/10] " Keith Busch
2025-11-17 19:57 ` Chang S. Bae
2025-11-21 18:55 ` Sean Christopherson

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