Re: [RFC PATCH 02/25] KVM: arm64: Save ID registers' sanitized value per vCPU

[Andrew Jones <drjones@redhat.com>]

On Mon, Oct 11, 2021 at 09:35:12PM -0700, Reiji Watanabe wrote:
> Extend sys_regs[] of kvm_cpu_context for ID registers and save ID
> registers' sanitized value in the array for the vCPU at the first
> vCPU reset. Use the saved ones when ID registers are read by
> userspace (via KVM_GET_ONE_REG) or the guest.
> 
> Signed-off-by: Reiji Watanabe <reijiw@google.com>
> ---
>  arch/arm64/include/asm/kvm_host.h | 10 ++++++++++
>  arch/arm64/kvm/sys_regs.c         | 26 ++++++++++++++++++--------
>  2 files changed, 28 insertions(+), 8 deletions(-)
> 
> diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
> index 9b5e7a3b6011..0cd351099adf 100644
> --- a/arch/arm64/include/asm/kvm_host.h
> +++ b/arch/arm64/include/asm/kvm_host.h
> @@ -145,6 +145,14 @@ struct kvm_vcpu_fault_info {
>  	u64 disr_el1;		/* Deferred [SError] Status Register */
>  };
>  
> +/*
> + * (Op0, Op1, CRn, CRm, Op2) of ID registers is (3, 0, 0, crm, op2),
> + * where 0<=crm<8, 0<=op2<8.

crm is 4 bits, so this should be 0 <= crm < 16 and...

> + */
> +#define KVM_ARM_ID_REG_MAX_NUM 64

...this should be 128. Or am I missing something?


> +#define IDREG_IDX(id)		((sys_reg_CRm(id) << 3) | sys_reg_Op2(id))
> +#define IDREG_SYS_IDX(id)	(ID_REG_BASE + IDREG_IDX(id))
> +
>  enum vcpu_sysreg {
>  	__INVALID_SYSREG__,   /* 0 is reserved as an invalid value */
>  	MPIDR_EL1,	/* MultiProcessor Affinity Register */
> @@ -209,6 +217,8 @@ enum vcpu_sysreg {
>  	CNTP_CVAL_EL0,
>  	CNTP_CTL_EL0,
>  
> +	ID_REG_BASE,
> +	ID_REG_END = ID_REG_BASE + KVM_ARM_ID_REG_MAX_NUM - 1,
>  	/* Memory Tagging Extension registers */
>  	RGSR_EL1,	/* Random Allocation Tag Seed Register */
>  	GCR_EL1,	/* Tag Control Register */
> diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c
> index 1d46e185f31e..72ca518e7944 100644
> --- a/arch/arm64/kvm/sys_regs.c
> +++ b/arch/arm64/kvm/sys_regs.c
> @@ -273,7 +273,7 @@ static bool trap_loregion(struct kvm_vcpu *vcpu,
>  			  struct sys_reg_params *p,
>  			  const struct sys_reg_desc *r)
>  {
> -	u64 val = read_sanitised_ftr_reg(SYS_ID_AA64MMFR1_EL1);
> +	u64 val = __vcpu_sys_reg(vcpu, IDREG_SYS_IDX(SYS_ID_AA64MMFR1_EL1));
>  	u32 sr = reg_to_encoding(r);
>  
>  	if (!(val & (0xfUL << ID_AA64MMFR1_LOR_SHIFT))) {
> @@ -1059,12 +1059,11 @@ static bool access_arch_timer(struct kvm_vcpu *vcpu,
>  	return true;
>  }
>  
> -/* Read a sanitised cpufeature ID register by sys_reg_desc */
>  static u64 read_id_reg(const struct kvm_vcpu *vcpu,
>  		struct sys_reg_desc const *r, bool raz)
>  {
>  	u32 id = reg_to_encoding(r);
> -	u64 val = raz ? 0 : read_sanitised_ftr_reg(id);
> +	u64 val = raz ? 0 : __vcpu_sys_reg(vcpu, IDREG_SYS_IDX(id));
>  
>  	switch (id) {
>  	case SYS_ID_AA64PFR0_EL1:
> @@ -1174,6 +1173,16 @@ static unsigned int sve_visibility(const struct kvm_vcpu *vcpu,
>  	return REG_HIDDEN;
>  }
>  
> +static void reset_id_reg(struct kvm_vcpu *vcpu, const struct sys_reg_desc *rd)

Since not all ID registers will use this, then maybe name it
reset_sanitised_id_reg?

> +{
> +	u32 id = reg_to_encoding(rd);
> +
> +	if (vcpu_has_reset_once(vcpu))
> +		return;

Ah, I see my kvm_vcpu_initialized() won't work since vcpu->arch.target is
set before the first reset. While vcpu->arch.target is only being used
like a "is_initialized" boolean at this time, I guess we better keep it
in case we ever want to implement CPU models (which this series gets us a
step closer to). 

> +
> +	__vcpu_sys_reg(vcpu, IDREG_SYS_IDX(id)) = read_sanitised_ftr_reg(id);
> +}
> +
>  static int set_id_aa64pfr0_el1(struct kvm_vcpu *vcpu,
>  			       const struct sys_reg_desc *rd,
>  			       const struct kvm_one_reg *reg, void __user *uaddr)
> @@ -1219,9 +1228,7 @@ static int set_id_aa64pfr0_el1(struct kvm_vcpu *vcpu,
>  /*
>   * cpufeature ID register user accessors
>   *
> - * For now, these registers are immutable for userspace, so no values
> - * are stored, and for set_id_reg() we don't allow the effective value
> - * to be changed.
> + * We don't allow the effective value to be changed.
>   */
>  static int __get_id_reg(const struct kvm_vcpu *vcpu,
>  			const struct sys_reg_desc *rd, void __user *uaddr,
> @@ -1375,6 +1382,7 @@ static unsigned int mte_visibility(const struct kvm_vcpu *vcpu,
>  #define ID_SANITISED(name) {			\
>  	SYS_DESC(SYS_##name),			\
>  	.access	= access_id_reg,		\
> +	.reset	= reset_id_reg,			\
>  	.get_user = get_id_reg,			\
>  	.set_user = set_id_reg,			\
>  	.visibility = id_visibility,		\
> @@ -1830,8 +1838,10 @@ static bool trap_dbgdidr(struct kvm_vcpu *vcpu,
>  	if (p->is_write) {
>  		return ignore_write(vcpu, p);
>  	} else {
> -		u64 dfr = read_sanitised_ftr_reg(SYS_ID_AA64DFR0_EL1);
> -		u64 pfr = read_sanitised_ftr_reg(SYS_ID_AA64PFR0_EL1);
> +		u64 dfr = __vcpu_sys_reg(vcpu,
> +					 IDREG_SYS_IDX(SYS_ID_AA64DFR0_EL1));
> +		u64 pfr = __vcpu_sys_reg(vcpu,
> +					 IDREG_SYS_IDX(SYS_ID_AA64PFR0_EL1));

Please avoid these ugly line breaks when we're well under Linux's max
length, which is 100.

>  		u32 el3 = !!cpuid_feature_extract_unsigned_field(pfr, ID_AA64PFR0_EL3_SHIFT);
>  
>  		p->regval = ((((dfr >> ID_AA64DFR0_WRPS_SHIFT) & 0xf) << 28) |
> -- 
> 2.33.0.882.g93a45727a2-goog
>

Thanks,
drew


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