Subject: Re: [PATCH 3/3] KVM: arm64: Add emulation for 32bit guests accessing ACTLR2

From: Marc Zyngier <[email-masked]>
Date: Thu, 28 May 2020 13:51:33 +0100

Hi James,

On 2020-05-26 17:18, James Morse wrote:
> ACTLR_EL1 is a 64bit register while the 32bit ACTLR is obviously 32bit.
> For 32bit software, the extra bits are accessible via ACTLR2... which
> KVM doesn't emulate.
> 
> Signed-off-by: James Morse <[email-masked]>
> ---
> I'm not convinced this is endian safe, but it does match what
> kvm_inject_undef32() do.
> 
> The alternative would be to always read the 64bit value, and generate
> the 32bit offets like access_vm_reg() does.
> 
>  arch/arm64/include/asm/kvm_host.h    |  1 +
>  arch/arm64/kvm/sys_regs_generic_v8.c | 16 +++++++++++++++-
>  2 files changed, 16 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/arm64/include/asm/kvm_host.h
> b/arch/arm64/include/asm/kvm_host.h
> index 32c8a675e5a4..5b7538663a8e 100644
> --- a/arch/arm64/include/asm/kvm_host.h
> +++ b/arch/arm64/include/asm/kvm_host.h
> @@ -185,6 +185,7 @@ enum vcpu_sysreg {
>  #define c0_CSSELR	(CSSELR_EL1 * 2)/* Cache Size Selection Register */
>  #define c1_SCTLR	(SCTLR_EL1 * 2)	/* System Control Register */
>  #define c1_ACTLR	(ACTLR_EL1 * 2)	/* Auxiliary Control Register */
> +#define c1_ACTLR2	(c1_ACTLR + 1)	/* ACTLR top 32 bits */
>  #define c1_CPACR	(CPACR_EL1 * 2)	/* Coprocessor Access Control */
>  #define c2_TTBR0	(TTBR0_EL1 * 2)	/* Translation Table Base Register 0 
> */
>  #define c2_TTBR0_high	(c2_TTBR0 + 1)	/* TTBR0 top 32 bits */
> diff --git a/arch/arm64/kvm/sys_regs_generic_v8.c
> b/arch/arm64/kvm/sys_regs_generic_v8.c
> index 9cb6b4c8355a..ed77bbb48e64 100644
> --- a/arch/arm64/kvm/sys_regs_generic_v8.c
> +++ b/arch/arm64/kvm/sys_regs_generic_v8.c
> @@ -30,6 +30,18 @@ static bool access_actlr(struct kvm_vcpu *vcpu,
>  	return true;
>  }
> 
> +static bool access_cp15_actlr(struct kvm_vcpu *vcpu,
> +			      struct sys_reg_params *p,
> +			      const struct sys_reg_desc *r)
> +{
> +	if (p->is_write)
> +		return ignore_write(vcpu, p);
> +
> +	p->regval = vcpu_cp15(vcpu, r->reg);
> +	return true;
> +
> +}
> +
>  static void reset_actlr(struct kvm_vcpu *vcpu, const struct 
> sys_reg_desc *r)
>  {
>  	__vcpu_sys_reg(vcpu, ACTLR_EL1) = read_sysreg(actlr_el1);
> @@ -46,7 +58,9 @@ static const struct sys_reg_desc genericv8_sys_regs[] 
> = {
>  static const struct sys_reg_desc genericv8_cp15_regs[] = {
>  	/* ACTLR */
>  	{ Op1(0b000), CRn(0b0001), CRm(0b0000), Op2(0b001),
> -	  access_actlr },
> +	  access_cp15_actlr, NULL, c1_ACTLR },
> +	{ Op1(0b000), CRn(0b0001), CRm(0b0000), Op2(0b011),
> +	  access_cp15_actlr, NULL, c1_ACTLR2 },
>  };
> 
>  static struct kvm_sys_reg_target_table genericv8_target_table = {

I'd get rid of any form of storage, and go with something like 
(untested, again):

diff --git a/arch/arm64/kvm/sys_regs_generic_v8.c 
b/arch/arm64/kvm/sys_regs_generic_v8.c
index 9cb6b4c8355a..1b2bf2d37612 100644
--- a/arch/arm64/kvm/sys_regs_generic_v8.c
+++ b/arch/arm64/kvm/sys_regs_generic_v8.c
@@ -26,13 +26,16 @@ static bool access_actlr(struct kvm_vcpu *vcpu,
  	if (p->is_write)
  		return ignore_write(vcpu, p);

-	p->regval = vcpu_read_sys_reg(vcpu, ACTLR_EL1);
-	return true;
-}
+	p->regval = read_sysreg(actlr_el1);

-static void reset_actlr(struct kvm_vcpu *vcpu, const struct 
sys_reg_desc *r)
-{
-	__vcpu_sys_reg(vcpu, ACTLR_EL1) = read_sysreg(actlr_el1);
+	if (p->aarch32) {
+		if (r->Op2 & 2)
+			p->regval = upper_32_bit(p->regval);
+		else
+			p->regval = lower_32_bit(p->regval);
+	}
+
+	return true;
  }

  /*
@@ -40,13 +43,13 @@ static void reset_actlr(struct kvm_vcpu *vcpu, const 
struct sys_reg_desc *r)
   * Important: Must be sorted ascending by Op0, Op1, CRn, CRm, Op2
   */
  static const struct sys_reg_desc genericv8_sys_regs[] = {
-	{ SYS_DESC(SYS_ACTLR_EL1), access_actlr, reset_actlr, ACTLR_EL1 },
+	{ SYS_DESC(SYS_ACTLR_EL1), access_actlr, },
  };

  static const struct sys_reg_desc genericv8_cp15_regs[] = {
  	/* ACTLR */
-	{ Op1(0b000), CRn(0b0001), CRm(0b0000), Op2(0b001),
-	  access_actlr },
+	{ Op1(0b000), CRn(0b0001), CRm(0b0000), Op2(0b001), access_actlr },
+	{ Op1(0b000), CRn(0b0001), CRm(0b0000), Op2(0b011), access_actlr },
  };

  static struct kvm_sys_reg_target_table genericv8_target_table = {

Thanks,

         M.
-- 
Jazz is not dead. It just smells funny...

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