Re: [PATCH] kvm: pass the virtual SEI syndrome to guest OS

[Marc Zyngier]

Please include James Morse on anything RAS related, as he's already
looking at related patches.

On 20/03/17 07:55, Dongjiu Geng wrote:
> In the RAS implementation, hardware pass the virtual SEI
> syndrome information through the VSESR_EL2, so set the virtual
> SEI syndrome using physical SEI syndrome el2_elr to pass to
> the guest OS
> 
> Signed-off-by: Dongjiu Geng <gengdongjiu@xxxxxxxxxx>
> Signed-off-by: Quanming wu <wuquanming@xxxxxxxxxx>
> ---
>  arch/arm64/Kconfig                   |  8 ++++++++
>  arch/arm64/include/asm/esr.h         |  1 +
>  arch/arm64/include/asm/kvm_emulate.h | 12 ++++++++++++
>  arch/arm64/include/asm/kvm_host.h    |  4 ++++
>  arch/arm64/kvm/hyp/switch.c          | 15 ++++++++++++++-
>  arch/arm64/kvm/inject_fault.c        | 10 ++++++++++
>  6 files changed, 49 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
> index 8c7c244247b6..ea62170a3b75 100644
> --- a/arch/arm64/Kconfig
> +++ b/arch/arm64/Kconfig
> @@ -908,6 +908,14 @@ endmenu
>  
>  menu "ARMv8.2 architectural features"
>  
> +config HAS_RAS_EXTENSION
> +	bool "Support arm64 RAS extension"
> +	default n
> +	help
> +	  Reliability, Availability, Serviceability(RAS; part of the ARMv8.2 Extensions).
> +
> +	  Selecting this option OS will try to recover the error that RAS hardware node detected.
> +

As this is an architectural extension, this should be controlled by the
CPU feature mechanism, and not be chosen at compile time. What you have
here will break horribly when booted on a CPU that doesn't implement RAS.

>  config ARM64_UAO
>  	bool "Enable support for User Access Override (UAO)"
>  	default y
> diff --git a/arch/arm64/include/asm/esr.h b/arch/arm64/include/asm/esr.h
> index d14c478976d0..e38d32b2bdad 100644
> --- a/arch/arm64/include/asm/esr.h
> +++ b/arch/arm64/include/asm/esr.h
> @@ -111,6 +111,7 @@
>  #define ESR_ELx_COND_MASK	(UL(0xF) << ESR_ELx_COND_SHIFT)
>  #define ESR_ELx_WFx_ISS_WFE	(UL(1) << 0)
>  #define ESR_ELx_xVC_IMM_MASK	((1UL << 16) - 1)
> +#define VSESR_ELx_IDS_ISS_MASK    ((1UL << 25) - 1)
>  
>  /* ESR value templates for specific events */
>  
> diff --git a/arch/arm64/include/asm/kvm_emulate.h b/arch/arm64/include/asm/kvm_emulate.h
> index f5ea0ba70f07..20d4da7f5dce 100644
> --- a/arch/arm64/include/asm/kvm_emulate.h
> +++ b/arch/arm64/include/asm/kvm_emulate.h
> @@ -148,6 +148,18 @@ static inline u32 kvm_vcpu_get_hsr(const struct kvm_vcpu *vcpu)
>  	return vcpu->arch.fault.esr_el2;
>  }
>  
> +#ifdef CONFIG_HAS_RAS_EXTENSION
> +static inline u32 kvm_vcpu_get_vsesr(const struct kvm_vcpu *vcpu)
> +{
> +	return vcpu->arch.fault.vsesr_el2;
> +}
> +
> +static inline void kvm_vcpu_set_vsesr(struct kvm_vcpu *vcpu, unsigned long val)
> +{
> +	vcpu->arch.fault.vsesr_el2 = val;
> +}
> +#endif
> +
>  static inline int kvm_vcpu_get_condition(const struct kvm_vcpu *vcpu)
>  {
>  	u32 esr = kvm_vcpu_get_hsr(vcpu);
> diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
> index e7705e7bb07b..f9e3bb57c461 100644
> --- a/arch/arm64/include/asm/kvm_host.h
> +++ b/arch/arm64/include/asm/kvm_host.h
> @@ -83,6 +83,10 @@ struct kvm_mmu_memory_cache {
>  };
>  
>  struct kvm_vcpu_fault_info {
> +#ifdef CONFIG_HAS_RAS_EXTENSION
> +	/* Virtual SError Exception Syndrome Register */
> +	u32 vsesr_el2;
> +#endif
>  	u32 esr_el2;		/* Hyp Syndrom Register */
>  	u64 far_el2;		/* Hyp Fault Address Register */
>  	u64 hpfar_el2;		/* Hyp IPA Fault Address Register */
> diff --git a/arch/arm64/kvm/hyp/switch.c b/arch/arm64/kvm/hyp/switch.c
> index aede1658aeda..770a153fb6ba 100644
> --- a/arch/arm64/kvm/hyp/switch.c
> +++ b/arch/arm64/kvm/hyp/switch.c
> @@ -86,6 +86,13 @@ static void __hyp_text __activate_traps(struct kvm_vcpu *vcpu)
>  		isb();
>  	}
>  	write_sysreg(val, hcr_el2);
> +#ifdef CONFIG_HAS_RAS_EXTENSION
> +	/* If virtual System Error or Asynchronous Abort is pending. set
> +	 * the virtual exception syndrome information
> +	 */
> +	if (vcpu->arch.hcr_el2 & HCR_VSE)
> +		write_sysreg(vcpu->arch.fault.vsesr_el2, vsesr_el2);
> +#endif
>  	/* Trap on AArch32 cp15 c15 accesses (EL1 or EL0) */
>  	write_sysreg(1 << 15, hstr_el2);
>  	/*
> @@ -139,8 +146,14 @@ static void __hyp_text __deactivate_traps(struct kvm_vcpu *vcpu)
>  	 * the crucial bit is "On taking a vSError interrupt,
>  	 * HCR_EL2.VSE is cleared to 0."
>  	 */
> -	if (vcpu->arch.hcr_el2 & HCR_VSE)
> +	if (vcpu->arch.hcr_el2 & HCR_VSE) {
>  		vcpu->arch.hcr_el2 = read_sysreg(hcr_el2);
> +#ifdef CONFIG_HAS_RAS_EXTENSION
> +		/* set vsesr_el2[24:0] with esr_el2[24:0] */
> +		kvm_vcpu_set_vsesr(vcpu, read_sysreg_el2(esr)
> +					& VSESR_ELx_IDS_ISS_MASK);

What guarantees that ESR_EL2 still contains the latest exception? What
does it mean to store something that is the current EL2 exception
syndrome together with an SError that has already been injected?

Also, is it correct to directly copy the ESR_EL2 bits into VSESR_EL2? My
own reading of the specification seem to imply that there is at least
differences when the guest is AArch32. Surely there would be some
processing here.

> +#endif
> +	}
>  
>  	__deactivate_traps_arch()();
>  	write_sysreg(0, hstr_el2);
> diff --git a/arch/arm64/kvm/inject_fault.c b/arch/arm64/kvm/inject_fault.c
> index da6a8cfa54a0..08a13dfe28a8 100644
> --- a/arch/arm64/kvm/inject_fault.c
> +++ b/arch/arm64/kvm/inject_fault.c
> @@ -242,4 +242,14 @@ void kvm_inject_undefined(struct kvm_vcpu *vcpu)
>  void kvm_inject_vabt(struct kvm_vcpu *vcpu)
>  {
>  	vcpu_set_hcr(vcpu, vcpu_get_hcr(vcpu) | HCR_VSE);
> +#ifdef CONFIG_HAS_RAS_EXTENSION
> +	/* If virtual System Error or Asynchronous Abort is set. set
> +	 * the virtual exception syndrome information
> +	 */
> +	kvm_vcpu_set_vsesr(vcpu, ((kvm_vcpu_get_vsesr(vcpu)
> +				& (~VSESR_ELx_IDS_ISS_MASK))
> +				| (kvm_vcpu_get_hsr(vcpu)
> +				& VSESR_ELx_IDS_ISS_MASK)));

What is the rational for setting VSESR_EL2 with the EL1 syndrome
information? That doesn't make any sense to me.

Overall, this patch is completely inconsistent and unclear in what it
tries to achieve. Also, as I already tated before, I'd like to see the
"firmware first" mode of operation be enforced here, going back to
userspace and let the VMM decide what to do.

Thanks,

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