Subject: Re: [PATCH v8 03/28] arm64: mte: CPU feature detection and initial sysreg configuration

From: Marc Zyngier <[email-masked]>
Date: Tue, 25 Aug 2020 09:53:16 +0100

On 2020-08-24 19:27, Catalin Marinas wrote:
> From: Vincenzo Frascino <[email-masked]>
> 
> Add the cpufeature and hwcap entries to detect the presence of MTE. Any
> secondary CPU not supporting the feature, if detected on the boot CPU,
> will be parked.
> 
> Add the minimum SCTLR_EL1 and HCR_EL2 bits for enabling MTE. The Normal
> Tagged memory type is configured in MAIR_EL1 before the MMU is enabled
> in order to avoid disrupting other CPUs in the CnP domain.
> 
> Signed-off-by: Vincenzo Frascino <[email-masked]>
> Co-developed-by: Catalin Marinas <[email-masked]>
> Signed-off-by: Catalin Marinas <[email-masked]>
> Cc: Will Deacon <[email-masked]>
> Cc: Marc Zyngier <[email-masked]>
> Cc: Suzuki K Poulose <[email-masked]>
> ---
> 
> Notes:
>     v8:
>     - Move the SCTLR_EL1, MAIR_EL1, GCR_EL1 and TFSR*_EL1 
> initialisation to
>       __cpu_setup before the MMU is enabled. While early MAIR_EL1 is
>       desirable to avoid conflicting with other CPUs in a CnP domain 
> the
>       TFSR_EL1 and GCR_EL1 will only come in handy later when support 
> for
>       in-kernel MTE is added.
> 
>     v7:
>     - Hide the MTE ID register field for guests until MTE gains support 
> for KVM.
> 
>  arch/arm64/include/asm/cpucaps.h    |  3 ++-
>  arch/arm64/include/asm/cpufeature.h |  6 ++++++
>  arch/arm64/include/asm/hwcap.h      |  2 +-
>  arch/arm64/include/asm/kvm_arm.h    |  2 +-
>  arch/arm64/include/asm/sysreg.h     |  1 +
>  arch/arm64/include/uapi/asm/hwcap.h |  2 +-
>  arch/arm64/kernel/cpufeature.c      | 17 +++++++++++++++++
>  arch/arm64/kernel/cpuinfo.c         |  2 +-
>  arch/arm64/kvm/sys_regs.c           |  2 ++
>  arch/arm64/mm/proc.S                | 24 ++++++++++++++++++++++++
>  10 files changed, 56 insertions(+), 5 deletions(-)
> 
> diff --git a/arch/arm64/include/asm/cpucaps.h 
> b/arch/arm64/include/asm/cpucaps.h
> index 07b643a70710..1937653b05a3 100644
> --- a/arch/arm64/include/asm/cpucaps.h
> +++ b/arch/arm64/include/asm/cpucaps.h
> @@ -64,7 +64,8 @@
>  #define ARM64_BTI				54
>  #define ARM64_HAS_ARMv8_4_TTL			55
>  #define ARM64_HAS_TLB_RANGE			56
> +#define ARM64_MTE				57
> 
> -#define ARM64_NCAPS				57
> +#define ARM64_NCAPS				58
> 
>  #endif /* __ASM_CPUCAPS_H */
> diff --git a/arch/arm64/include/asm/cpufeature.h
> b/arch/arm64/include/asm/cpufeature.h
> index 89b4f0142c28..680b5b36ddd5 100644
> --- a/arch/arm64/include/asm/cpufeature.h
> +++ b/arch/arm64/include/asm/cpufeature.h
> @@ -681,6 +681,12 @@ static __always_inline bool
> system_uses_irq_prio_masking(void)
>  	       cpus_have_const_cap(ARM64_HAS_IRQ_PRIO_MASKING);
>  }
> 
> +static inline bool system_supports_mte(void)
> +{
> +	return IS_ENABLED(CONFIG_ARM64_MTE) &&
> +		cpus_have_const_cap(ARM64_MTE);
> +}
> +
>  static inline bool system_has_prio_mask_debugging(void)
>  {
>  	return IS_ENABLED(CONFIG_ARM64_DEBUG_PRIORITY_MASKING) &&
> diff --git a/arch/arm64/include/asm/hwcap.h 
> b/arch/arm64/include/asm/hwcap.h
> index 22f73fe09030..0d4a6741b6a5 100644
> --- a/arch/arm64/include/asm/hwcap.h
> +++ b/arch/arm64/include/asm/hwcap.h
> @@ -95,7 +95,7 @@
>  #define KERNEL_HWCAP_DGH		__khwcap2_feature(DGH)
>  #define KERNEL_HWCAP_RNG		__khwcap2_feature(RNG)
>  #define KERNEL_HWCAP_BTI		__khwcap2_feature(BTI)
> -/* reserved for KERNEL_HWCAP_MTE	__khwcap2_feature(MTE) */
> +#define KERNEL_HWCAP_MTE		__khwcap2_feature(MTE)
> 
>  /*
>   * This yields a mask that user programs can use to figure out what
> diff --git a/arch/arm64/include/asm/kvm_arm.h 
> b/arch/arm64/include/asm/kvm_arm.h
> index 8a1cbfd544d6..6c3b2fc922bb 100644
> --- a/arch/arm64/include/asm/kvm_arm.h
> +++ b/arch/arm64/include/asm/kvm_arm.h
> @@ -78,7 +78,7 @@
>  			 HCR_AMO | HCR_SWIO | HCR_TIDCP | HCR_RW | HCR_TLOR | \
>  			 HCR_FMO | HCR_IMO)
>  #define HCR_VIRT_EXCP_MASK (HCR_VSE | HCR_VI | HCR_VF)
> -#define HCR_HOST_NVHE_FLAGS (HCR_RW | HCR_API | HCR_APK)
> +#define HCR_HOST_NVHE_FLAGS (HCR_RW | HCR_API | HCR_APK | HCR_ATA)
>  #define HCR_HOST_VHE_FLAGS (HCR_RW | HCR_TGE | HCR_E2H)

Why is HCR_ATA only set for nVHE? HCR_EL2.ATA seems to apply to both,
doesn't it?

> 
>  /* TCR_EL2 Registers bits */

[...]

> diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c
> index 077293b5115f..59b91f58efec 100644
> --- a/arch/arm64/kvm/sys_regs.c
> +++ b/arch/arm64/kvm/sys_regs.c
> @@ -1131,6 +1131,8 @@ static u64 read_id_reg(const struct kvm_vcpu 
> *vcpu,
>  		if (!vcpu_has_sve(vcpu))
>  			val &= ~(0xfUL << ID_AA64PFR0_SVE_SHIFT);
>  		val &= ~(0xfUL << ID_AA64PFR0_AMU_SHIFT);
> +	} else if (id == SYS_ID_AA64PFR1_EL1) {
> +		val &= ~(0xfUL << ID_AA64PFR1_MTE_SHIFT);

Hiding the capability is fine, but where is the handling of trapping
instructions done? They should result in an UNDEF being injected.

Thanks,

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

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