[PATCH v3 2/3] KVM/arm/arm64: enable enhanced armv7 fp/simd lazy switch

Mario Smarduch m.smarduch at samsung.com
Fri Oct 30 14:56:32 PDT 2015


This patch tracks vfp/simd hardware state with a vcpu lazy flag. vCPU lazy 
flag is set on guest access and traps to vfp/simd hardware switch handler. On 
vm-enter if lazy flag is set skip trap enable and save host fpexc. On 
vm-exit if flag is set skip hardware context switch and return to host with 
guest context. In vcpu_put check if vcpu lazy flag is set, and execute a 
hardware context switch to restore host.

Also some arm64 field and empty function are added to compile for arm64.

Signed-off-by: Mario Smarduch <m.smarduch at samsung.com>
---
 arch/arm/include/asm/kvm_host.h   |  1 +
 arch/arm/kvm/arm.c                |  6 ++++
 arch/arm/kvm/interrupts.S         | 60 ++++++++++++++++++++++++++++-----------
 arch/arm/kvm/interrupts_head.S    | 14 +++++----
 arch/arm64/include/asm/kvm_host.h |  4 +++
 5 files changed, 63 insertions(+), 22 deletions(-)

diff --git a/arch/arm/include/asm/kvm_host.h b/arch/arm/include/asm/kvm_host.h
index f1bf551..a9e86e0 100644
--- a/arch/arm/include/asm/kvm_host.h
+++ b/arch/arm/include/asm/kvm_host.h
@@ -227,6 +227,7 @@ int kvm_perf_teardown(void);
 void kvm_mmu_wp_memory_region(struct kvm *kvm, int slot);
 
 struct kvm_vcpu *kvm_mpidr_to_vcpu(struct kvm *kvm, unsigned long mpidr);
+void kvm_restore_host_vfp_state(struct kvm_vcpu *);
 
 static inline void kvm_arch_hardware_disable(void) {}
 static inline void kvm_arch_hardware_unsetup(void) {}
diff --git a/arch/arm/kvm/arm.c b/arch/arm/kvm/arm.c
index dc017ad..11a56fe 100644
--- a/arch/arm/kvm/arm.c
+++ b/arch/arm/kvm/arm.c
@@ -296,6 +296,12 @@ void kvm_arch_vcpu_load(struct kvm_vcpu *vcpu, int cpu)
 void kvm_arch_vcpu_put(struct kvm_vcpu *vcpu)
 {
 	/*
+	 * If fp/simd registers are dirty save guest, restore host before
+	 * releasing the cpu.
+	 */
+	if (vcpu->arch.vfp_dirty)
+		kvm_restore_host_vfp_state(vcpu);
+	/*
 	 * The arch-generic KVM code expects the cpu field of a vcpu to be -1
 	 * if the vcpu is no longer assigned to a cpu.  This is used for the
 	 * optimized make_all_cpus_request path.
diff --git a/arch/arm/kvm/interrupts.S b/arch/arm/kvm/interrupts.S
index 900ef6d..ca25314 100644
--- a/arch/arm/kvm/interrupts.S
+++ b/arch/arm/kvm/interrupts.S
@@ -28,6 +28,32 @@
 #include "interrupts_head.S"
 
 	.text
+/**
+ * void kvm_restore_host_vfp_state(struct vcpu *vcpu) - Executes lazy
+ * 	fp/simd switch, saves the guest, restores host. Called from host
+ *	mode, placed outside of hyp region start/end.
+ */
+ENTRY(kvm_restore_host_vfp_state)
+#ifdef CONFIG_VFPv3
+	push    {r4-r7}
+
+	add     r7, vcpu, #VCPU_VFP_GUEST
+	store_vfp_state r7
+
+	add     r7, vcpu, #VCPU_VFP_HOST
+	ldr     r7, [r7]
+	restore_vfp_state r7
+
+	ldr     r3, [vcpu, #VCPU_VFP_HOST_FPEXC]
+	VFPFMXR FPEXC, r3
+
+	mov     r3, #0
+	strb    r3, [vcpu, #VCPU_VFP_DIRTY]
+
+	pop     {r4-r7}
+#endif
+	bx      lr
+ENDPROC(kvm_restore_host_vfp_state)
 
 __kvm_hyp_code_start:
 	.globl __kvm_hyp_code_start
@@ -119,11 +145,16 @@ ENTRY(__kvm_vcpu_run)
 	@ If the host kernel has not been configured with VFPv3 support,
 	@ then it is safer if we deny guests from using it as well.
 #ifdef CONFIG_VFPv3
-	@ Set FPEXC_EN so the guest doesn't trap floating point instructions
+	@ fp/simd register file has already been accessed, so skip host fpexc
+	@ save and access trap enable.
+	vfp_inlazy_mode r7, skip_guest_vfp_trap
+
 	VFPFMRX r2, FPEXC		@ VMRS
-	push	{r2}
+	str     r2, [vcpu, #VCPU_VFP_HOST_FPEXC]
 	orr	r2, r2, #FPEXC_EN
 	VFPFMXR FPEXC, r2		@ VMSR
+	set_hcptr vmentry, (HCPTR_TCP(10) | HCPTR_TCP(11))
+skip_guest_vfp_trap:
 #endif
 
 	@ Configure Hyp-role
@@ -131,7 +162,7 @@ ENTRY(__kvm_vcpu_run)
 
 	@ Trap coprocessor CRx accesses
 	set_hstr vmentry
-	set_hcptr vmentry, (HCPTR_TTA | HCPTR_TCP(10) | HCPTR_TCP(11))
+	set_hcptr vmentry, (HCPTR_TTA)
 	set_hdcr vmentry
 
 	@ Write configured ID register into MIDR alias
@@ -170,22 +201,15 @@ __kvm_vcpu_return:
 	@ Don't trap coprocessor accesses for host kernel
 	set_hstr vmexit
 	set_hdcr vmexit
-	set_hcptr vmexit, (HCPTR_TTA | HCPTR_TCP(10) | HCPTR_TCP(11)), after_vfp_restore
+	set_hcptr vmexit, (HCPTR_TTA | HCPTR_TCP(10) | HCPTR_TCP(11))
 
 #ifdef CONFIG_VFPv3
-	@ Switch VFP/NEON hardware state to the host's
-	add	r7, vcpu, #VCPU_VFP_GUEST
-	store_vfp_state r7
-	add	r7, vcpu, #VCPU_VFP_HOST
-	ldr	r7, [r7]
-	restore_vfp_state r7
-
-after_vfp_restore:
-	@ Restore FPEXC_EN which we clobbered on entry
-	pop	{r2}
+	@ If fp/simd not dirty, restore FPEXC which we clobbered on entry.
+	@ Otherwise return with guest FPEXC, later saved in vcpu_put.
+	vfp_inlazy_mode r2, skip_restore_host_fpexc
+	ldr     r2, [vcpu, #VCPU_VFP_HOST_FPEXC]
 	VFPFMXR FPEXC, r2
-#else
-after_vfp_restore:
+skip_restore_host_fpexc:
 #endif
 
 	@ Reset Hyp-role
@@ -485,6 +509,10 @@ switch_to_guest_vfp:
 	@ NEON/VFP used.  Turn on VFP access.
 	set_hcptr vmtrap, (HCPTR_TCP(10) | HCPTR_TCP(11))
 
+	@ set lazy mode flag, switch hardware context on vcpu_put
+	mov     r1, #1
+	strb    r1, [vcpu, #VCPU_VFP_DIRTY]
+
 	@ Switch VFP/NEON hardware state to the guest's
 	add	r7, r0, #VCPU_VFP_HOST
 	ldr	r7, [r7]
diff --git a/arch/arm/kvm/interrupts_head.S b/arch/arm/kvm/interrupts_head.S
index 51a5950..34e71ee 100644
--- a/arch/arm/kvm/interrupts_head.S
+++ b/arch/arm/kvm/interrupts_head.S
@@ -593,10 +593,8 @@ ARM_BE8(rev	r6, r6  )
  * (hardware reset value is 0). Keep previous value in r2.
  * An ISB is emited on vmexit/vmtrap, but executed on vmexit only if
  * VFP wasn't already enabled (always executed on vmtrap).
- * If a label is specified with vmexit, it is branched to if VFP wasn't
- * enabled.
  */
-.macro set_hcptr operation, mask, label = none
+.macro set_hcptr operation, mask
 	mrc	p15, 4, r2, c1, c1, 2
 	ldr	r3, =\mask
 	.if \operation == vmentry
@@ -611,13 +609,17 @@ ARM_BE8(rev	r6, r6  )
 	beq	1f
 	.endif
 	isb
-	.if \label != none
-	b	\label
-	.endif
 1:
 	.endif
 .endm
 
+/* Checks if VFP/SIMD dirty flag is set, if it is branch to label. */
+.macro vfp_inlazy_mode, reg, label
+	ldr	\reg, [vcpu, #VCPU_VFP_DIRTY]
+	cmp	\reg, #1
+	beq	\label
+.endm
+
 /* Configures the HDCR (Hyp Debug Configuration Register) on entry/return
  * (hardware reset value is 0) */
 .macro set_hdcr operation
diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
index 4562459..26a2347 100644
--- a/arch/arm64/include/asm/kvm_host.h
+++ b/arch/arm64/include/asm/kvm_host.h
@@ -157,6 +157,9 @@ struct kvm_vcpu_arch {
 	/* Interrupt related fields */
 	u64 irq_lines;		/* IRQ and FIQ levels */
 
+	/* fp/simd dirty flag true if guest accessed register file */
+	bool    vfp_dirty;
+
 	/* Cache some mmu pages needed inside spinlock regions */
 	struct kvm_mmu_memory_cache mmu_page_cache;
 
@@ -248,6 +251,7 @@ static inline void kvm_arch_hardware_unsetup(void) {}
 static inline void kvm_arch_sync_events(struct kvm *kvm) {}
 static inline void kvm_arch_vcpu_uninit(struct kvm_vcpu *vcpu) {}
 static inline void kvm_arch_sched_in(struct kvm_vcpu *vcpu, int cpu) {}
+static inline void kvm_restore_host_vfp_state(struct kvm_vcpu *vcpu) {}
 
 void kvm_arm_init_debug(void);
 void kvm_arm_setup_debug(struct kvm_vcpu *vcpu);
-- 
1.9.1




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