Re: [PATCH v4 29/40] KVM: arm64: Prepare to handle deferred save/restore of 32-bit registers

Julien Grall <julien.grall@xxxxxxx> · Fri, 23 Feb 2018 11:35:38 +0000

Hi Christoffer,

On 15/02/18 21:03, Christoffer Dall wrote:
32-bit registers are not used by a 64-bit host kernel and can be
deferred, but we need to rework the accesses to this register to access
the latest value depending on whether or not guest system registers are
loaded on the CPU or only reside in memory.

I realize that you explain in the new patch why FPEXC32_EL2 is not 
directly accessed below. But I think it might be worth to explain it 
here as well because the commit message implies all 32-bit registers 
could be deferred.


Signed-off-by: Christoffer Dall <christoffer.dall@xxxxxxxxxx>
---

Notes:
     Changes since v3:
      - Don't also try to write hardware spsr when sysregs are not loaded
      - Adapted patch to use switch-based sysreg save/restore approach
      - (Kept additional BUG_ON() in vcpu_read_spsr32() to keep the compiler happy)
     
     Changes since v2:
      - New patch (deferred register handling has been reworked)

  arch/arm64/include/asm/kvm_emulate.h | 32 +++++------------
  arch/arm64/kvm/regmap.c              | 67 +++++++++++++++++++++++++++---------
  arch/arm64/kvm/sys_regs.c            |  6 ++++
  3 files changed, 65 insertions(+), 40 deletions(-)

diff --git a/arch/arm64/include/asm/kvm_emulate.h b/arch/arm64/include/asm/kvm_emulate.h
index 9cb13b23c7a1..23b33e8ea03a 100644
--- a/arch/arm64/include/asm/kvm_emulate.h
+++ b/arch/arm64/include/asm/kvm_emulate.h
@@ -33,7 +33,8 @@
  #include <asm/virt.h>
  
  unsigned long *vcpu_reg32(const struct kvm_vcpu *vcpu, u8 reg_num);
-unsigned long *vcpu_spsr32(const struct kvm_vcpu *vcpu);
+unsigned long vcpu_read_spsr32(const struct kvm_vcpu *vcpu);
+void vcpu_write_spsr32(struct kvm_vcpu *vcpu, unsigned long v);
  
  bool kvm_condition_valid32(const struct kvm_vcpu *vcpu);
  void kvm_skip_instr32(struct kvm_vcpu *vcpu, bool is_wide_instr);
@@ -162,41 +163,26 @@ static inline void vcpu_set_reg(struct kvm_vcpu *vcpu, u8 reg_num,
  
  static inline unsigned long vcpu_read_spsr(const struct kvm_vcpu *vcpu)
  {
-	unsigned long *p = (unsigned long *)&vcpu_gp_regs(vcpu)->spsr[KVM_SPSR_EL1];
-
-	if (vcpu_mode_is_32bit(vcpu)) {
-		unsigned long *p_32bit = vcpu_spsr32(vcpu);
-
-		/* KVM_SPSR_SVC aliases KVM_SPSR_EL1 */
-		if (p_32bit != (unsigned long *)p)
-			return *p_32bit;
-	}
+	if (vcpu_mode_is_32bit(vcpu))
+		return vcpu_read_spsr32(vcpu);
  
  	if (vcpu->arch.sysregs_loaded_on_cpu)
  		return read_sysreg_el1(spsr);
  	else
-		return *p;
+		return vcpu_gp_regs(vcpu)->spsr[KVM_SPSR_EL1];
  }
  
-static inline void vcpu_write_spsr(const struct kvm_vcpu *vcpu, unsigned long v)
+static inline void vcpu_write_spsr(struct kvm_vcpu *vcpu, unsigned long v)
  {
-	unsigned long *p = (unsigned long *)&vcpu_gp_regs(vcpu)->spsr[KVM_SPSR_EL1];
-
-	/* KVM_SPSR_SVC aliases KVM_SPSR_EL1 */
  	if (vcpu_mode_is_32bit(vcpu)) {
-		unsigned long *p_32bit = vcpu_spsr32(vcpu);
-
-		/* KVM_SPSR_SVC aliases KVM_SPSR_EL1 */
-		if (p_32bit != (unsigned long *)p) {
-			*p_32bit = v;
-			return;
-		}
+		vcpu_write_spsr32(vcpu, v);
+		return;
  	}
  
  	if (vcpu->arch.sysregs_loaded_on_cpu)
  		write_sysreg_el1(v, spsr);
  	else
-		*p = v;
+		vcpu_gp_regs(vcpu)->spsr[KVM_SPSR_EL1] = v;
  }
  
  static inline bool vcpu_mode_priv(const struct kvm_vcpu *vcpu)
diff --git a/arch/arm64/kvm/regmap.c b/arch/arm64/kvm/regmap.c
index bbc6ae32e4af..eefe403a2e63 100644
--- a/arch/arm64/kvm/regmap.c
+++ b/arch/arm64/kvm/regmap.c
@@ -141,28 +141,61 @@ unsigned long *vcpu_reg32(const struct kvm_vcpu *vcpu, u8 reg_num)
  /*
   * Return the SPSR for the current mode of the virtual CPU.
   */
-unsigned long *vcpu_spsr32(const struct kvm_vcpu *vcpu)
+static int vcpu_spsr32_mode(const struct kvm_vcpu *vcpu)
  {
  	unsigned long mode = *vcpu_cpsr(vcpu) & COMPAT_PSR_MODE_MASK;
  	switch (mode) {
-	case COMPAT_PSR_MODE_SVC:
-		mode = KVM_SPSR_SVC;
-		break;
-	case COMPAT_PSR_MODE_ABT:
-		mode = KVM_SPSR_ABT;
-		break;
-	case COMPAT_PSR_MODE_UND:
-		mode = KVM_SPSR_UND;
-		break;
-	case COMPAT_PSR_MODE_IRQ:
-		mode = KVM_SPSR_IRQ;
-		break;
-	case COMPAT_PSR_MODE_FIQ:
-		mode = KVM_SPSR_FIQ;
-		break;
+	case COMPAT_PSR_MODE_SVC: return KVM_SPSR_SVC;
+	case COMPAT_PSR_MODE_ABT: return KVM_SPSR_ABT;
+	case COMPAT_PSR_MODE_UND: return KVM_SPSR_UND;
+	case COMPAT_PSR_MODE_IRQ: return KVM_SPSR_IRQ;
+	case COMPAT_PSR_MODE_FIQ: return KVM_SPSR_FIQ;
+	default: BUG();
+	}
+}
+
+unsigned long vcpu_read_spsr32(const struct kvm_vcpu *vcpu)
+{
+	int spsr_idx = vcpu_spsr32_mode(vcpu);
+
+	if (!vcpu->arch.sysregs_loaded_on_cpu)
+		return vcpu_gp_regs(vcpu)->spsr[spsr_idx];
+
+	switch (spsr_idx) {
+	case KVM_SPSR_SVC:
+		return read_sysreg_el1(spsr);
+	case KVM_SPSR_ABT:
+		return read_sysreg(spsr_abt);
+	case KVM_SPSR_UND:
+		return read_sysreg(spsr_und);
+	case KVM_SPSR_IRQ:
+		return read_sysreg(spsr_irq);
+	case KVM_SPSR_FIQ:
+		return read_sysreg(spsr_fiq);
  	default:
  		BUG();
  	}
+}
+
+void vcpu_write_spsr32(struct kvm_vcpu *vcpu, unsigned long v)
+{
+	int spsr_idx = vcpu_spsr32_mode(vcpu);
+
+	if (!vcpu->arch.sysregs_loaded_on_cpu) {
+		vcpu_gp_regs(vcpu)->spsr[spsr_idx] = v;
+		return;
+	}
  
-	return (unsigned long *)&vcpu_gp_regs(vcpu)->spsr[mode];
+	switch (spsr_idx) {
+	case KVM_SPSR_SVC:
+		write_sysreg_el1(v, spsr);
+	case KVM_SPSR_ABT:
+		write_sysreg(v, spsr_abt);
+	case KVM_SPSR_UND:
+		write_sysreg(v, spsr_und);
+	case KVM_SPSR_IRQ:
+		write_sysreg(v, spsr_irq);
+	case KVM_SPSR_FIQ:
+		write_sysreg(v, spsr_fiq);
+	}
  }
diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c
index f060309337aa..d2324560c9f5 100644
--- a/arch/arm64/kvm/sys_regs.c
+++ b/arch/arm64/kvm/sys_regs.c
@@ -107,6 +107,9 @@ u64 vcpu_read_sys_reg(struct kvm_vcpu *vcpu, int reg)
  	case AMAIR_EL1:		return read_sysreg_s(amair_EL12);
  	case CNTKCTL_EL1:	return read_sysreg_s(cntkctl_EL12);
  	case PAR_EL1:		return read_sysreg_s(SYS_PAR_EL1);
+	case DACR32_EL2:	return read_sysreg_s(SYS_DACR32_EL2);
+	case IFSR32_EL2:	return read_sysreg_s(SYS_IFSR32_EL2);
+	case DBGVCR32_EL2:	return read_sysreg_s(SYS_DBGVCR32_EL2);
  	}
  
  immediate_read:
@@ -143,6 +146,9 @@ void vcpu_write_sys_reg(struct kvm_vcpu *vcpu, int reg, u64 val)
  	case AMAIR_EL1:		write_sysreg_s(val, amair_EL12);	return;
  	case CNTKCTL_EL1:	write_sysreg_s(val, cntkctl_EL12);	return;
  	case PAR_EL1:		write_sysreg_s(val, SYS_PAR_EL1);	return;
+	case DACR32_EL2:	write_sysreg_s(val, SYS_DACR32_EL2);	return;
+	case IFSR32_EL2:	write_sysreg_s(val, SYS_IFSR32_EL2);	return;
+	case DBGVCR32_EL2:	write_sysreg_s(val, SYS_DBGVCR32_EL2);	return;
  	}
  
  immediate_write:


Cheers,

--
Julien Grall






