linux-kernel - [PATCH 07/13] arm64: KVM: VHE: Patch out use of HVC

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Message-Id: <1436372356-30410-8-git-send-email-marc.zyngier@arm.com>
Date:	Wed,  8 Jul 2015 17:19:10 +0100
From:	Marc Zyngier <marc.zyngier@....com>
To:	Catalin Marinas <catalin.marinas@....com>,
	Will Deacon <will.deacon@....com>,
	Christoffer Dall <christoffer.dall@...aro.org>
Cc:	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	kvm@...r.kernel.org, kvmarm@...ts.cs.columbia.edu
Subject: [PATCH 07/13] arm64: KVM: VHE: Patch out use of HVC

With VHE, the host never issues an HVC instruction to get into the
KVM code, as we can simply branch there.

Use runtime code patching to simplify things a bit.

Signed-off-by: Marc Zyngier <marc.zyngier@....com>
---
 arch/arm64/kvm/hyp.S        | 43 ++++++++++++++++++++++++++++++++++++-------
 arch/arm64/kvm/vhe-macros.h | 36 ++++++++++++++++++++++++++++++++++++
 2 files changed, 72 insertions(+), 7 deletions(-)
 create mode 100644 arch/arm64/kvm/vhe-macros.h

diff --git a/arch/arm64/kvm/hyp.S b/arch/arm64/kvm/hyp.S
index 17a8fb1..a65e053 100644
--- a/arch/arm64/kvm/hyp.S
+++ b/arch/arm64/kvm/hyp.S
@@ -30,6 +30,8 @@
 #include <asm/kvm_mmu.h>
 #include <asm/memory.h>
 
+#include "vhe-macros.h"
+
 #define CPU_GP_REG_OFFSET(x)	(CPU_GP_REGS + x)
 #define CPU_XREG_OFFSET(x)	CPU_GP_REG_OFFSET(CPU_USER_PT_REGS + 8*x)
 #define CPU_SPSR_OFFSET(x)	CPU_GP_REG_OFFSET(CPU_SPSR + 8*x)
@@ -39,6 +41,19 @@
 	.pushsection	.hyp.text, "ax"
 	.align	PAGE_SHIFT
 
+.macro do_el2_call
+	/*
+	 * Shuffle the parameters before calling the function
+	 * pointed to in x0. Assumes parameters in x[1,2,3],
+	 * clobbers lr.
+	 */
+	mov     lr, x0
+	mov     x0, x1
+	mov     x1, x2
+	mov     x2, x3
+	blr     lr
+.endm
+
 .macro save_common_regs
 	// x2: base address for cpu context
 	// x3: tmp register
@@ -1124,7 +1139,23 @@ __hyp_panic_str:
  * arch/arm64/kernel/hyp_stub.S.
  */
 ENTRY(kvm_call_hyp)
-	hvc	#0
+	/*
+	 * NOP out the hvc/ret sequence on VHE, and fall through.
+	 */
+ifnvhe	hvc #0,					nop
+ifnvhe	ret,				       "push	lr, xzr"
+
+	do_el2_call
+
+	/*
+	 * We used to rely on having an exception return to get
+	 * an implicit isb. In the E2H case, we don't have it anymore.
+	 * rather than changing all the leaf functions, just do it here
+	 * before returning to the rest of the kernel.
+	 */
+	isb
+
+	pop     lr, xzr
 	ret
 ENDPROC(kvm_call_hyp)
 
@@ -1156,7 +1187,9 @@ el1_sync:					// Guest trapped into EL2
 	mrs	x1, esr_el2
 	lsr	x2, x1, #ESR_ELx_EC_SHIFT
 
-	cmp	x2, #ESR_ELx_EC_HVC64
+	// Ugly shortcut for VHE. We can do this early because the
+	// host cannot do an HVC.
+ifnvhe  _S_(cmp	x2, #ESR_ELx_EC_HVC64),		"b	el1_trap"
 	b.ne	el1_trap
 
 	mrs	x3, vttbr_el2			// If vttbr is valid, the 64bit guest
@@ -1177,11 +1210,7 @@ el1_sync:					// Guest trapped into EL2
 	 * Compute the function address in EL2, and shuffle the parameters.
 	 */
 	kern_hyp_va	x0
-	mov	lr, x0
-	mov	x0, x1
-	mov	x1, x2
-	mov	x2, x3
-	blr	lr
+	do_el2_call
 
 	pop	lr, xzr
 2:	eret
diff --git a/arch/arm64/kvm/vhe-macros.h b/arch/arm64/kvm/vhe-macros.h
new file mode 100644
index 0000000..da7f9da
--- /dev/null
+++ b/arch/arm64/kvm/vhe-macros.h
@@ -0,0 +1,36 @@
+/*
+ * Copyright (C) 2015 - ARM Ltd
+ * Author: Marc Zyngier <marc.zyngier@....com>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#ifndef __ARM64_VHE_MACROS_H__
+#define __ARM64_VHE_MACROS_H__
+
+#include <asm/alternative.h>
+#include <asm/cpufeature.h>
+
+#ifdef __ASSEMBLY__
+
+/* Hack to allow stringification of macros... */
+#define __S__(a,args...)	__stringify(a, ##args)
+#define _S_(a,args...)		__S__(a, args)
+
+.macro ifnvhe nonvhe vhe
+	alternative_insn	"\nonvhe", "\vhe", ARM64_HAS_VIRT_HOST_EXTN
+.endm
+
+#endif
+
+#endif	/*__ARM64_VHE_MACROS_H__  */
-- 
2.1.4

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