Re: [PATCH v3 2/3] arm64: kvm: inject SError with virtual syndrome

[Christoffer Dall <cdall@linaro.org>]

On Sun, Apr 30, 2017 at 01:37:56PM +0800, Dongjiu Geng wrote:
> when SError happen, kvm notifies kvmtool to generate GHES table
> to record the error, then kvmtools inject the SError with specified

again, is this really specific to kvmtool?  Pleae try to explain this
mechanism in generic terms.

> virtual syndrome. when switch to guest, a virtual SError will happen with
> this specified syndrome.
> 
> Signed-off-by: Dongjiu Geng <gengdongjiu@huawei.com>
> ---
>  arch/arm64/include/asm/esr.h         |  2 ++
>  arch/arm64/include/asm/kvm_emulate.h | 10 ++++++++++
>  arch/arm64/include/asm/kvm_host.h    |  1 +
>  arch/arm64/include/asm/sysreg.h      |  3 +++
>  arch/arm64/kvm/handle_exit.c         | 25 +++++++++++++++++++------
>  arch/arm64/kvm/hyp/switch.c          | 15 ++++++++++++++-
>  include/uapi/linux/kvm.h             |  5 +++++
>  7 files changed, 54 insertions(+), 7 deletions(-)
> 
> diff --git a/arch/arm64/include/asm/esr.h b/arch/arm64/include/asm/esr.h
> index 22f9c90..d009c99 100644
> --- a/arch/arm64/include/asm/esr.h
> +++ b/arch/arm64/include/asm/esr.h
> @@ -127,6 +127,8 @@
>  #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 */
>  
>  /* BRK instruction trap from AArch64 state */
> diff --git a/arch/arm64/include/asm/kvm_emulate.h b/arch/arm64/include/asm/kvm_emulate.h
> index f5ea0ba..a3259a9 100644
> --- a/arch/arm64/include/asm/kvm_emulate.h
> +++ b/arch/arm64/include/asm/kvm_emulate.h
> @@ -148,6 +148,16 @@ static inline u32 kvm_vcpu_get_hsr(const struct kvm_vcpu *vcpu)
>  	return vcpu->arch.fault.esr_el2;
>  }
>  
> +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;
> +}
> +
>  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 e7705e7..84ed239 100644
> --- a/arch/arm64/include/asm/kvm_host.h
> +++ b/arch/arm64/include/asm/kvm_host.h
> @@ -86,6 +86,7 @@ struct kvm_vcpu_fault_info {
>  	u32 esr_el2;		/* Hyp Syndrom Register */
>  	u64 far_el2;		/* Hyp Fault Address Register */
>  	u64 hpfar_el2;		/* Hyp IPA Fault Address Register */
> +	u32 vsesr_el2;		/* Virtual SError Exception Syndrome Register */
>  };
>  
>  /*
> diff --git a/arch/arm64/include/asm/sysreg.h b/arch/arm64/include/asm/sysreg.h
> index 32964c7..b6afb7a 100644
> --- a/arch/arm64/include/asm/sysreg.h
> +++ b/arch/arm64/include/asm/sysreg.h
> @@ -125,6 +125,9 @@
>  #define REG_PSTATE_PAN_IMM		sys_reg(0, 0, 4, 0, 4)
>  #define REG_PSTATE_UAO_IMM		sys_reg(0, 0, 4, 0, 3)
>  
> +#define VSESR_EL2			sys_reg(3, 4, 5, 2, 3)
> +
> +
>  #define SET_PSTATE_PAN(x) __emit_inst(0xd5000000 | REG_PSTATE_PAN_IMM |	\
>  				      (!!x)<<8 | 0x1f)
>  #define SET_PSTATE_UAO(x) __emit_inst(0xd5000000 | REG_PSTATE_UAO_IMM |	\
> diff --git a/arch/arm64/kvm/handle_exit.c b/arch/arm64/kvm/handle_exit.c
> index c89d83a..3d024a9 100644
> --- a/arch/arm64/kvm/handle_exit.c
> +++ b/arch/arm64/kvm/handle_exit.c
> @@ -180,7 +180,11 @@ static exit_handle_fn kvm_get_exit_handler(struct kvm_vcpu *vcpu)
>  
>  static int kvm_handle_guest_sei(struct kvm_vcpu *vcpu, struct kvm_run *run)
>  {
> -	unsigned long fault_ipa = kvm_vcpu_get_fault_ipa(vcpu);
> +	unsigned long hva, fault_ipa = kvm_vcpu_get_fault_ipa(vcpu);
> +	struct kvm_memory_slot *memslot;
> +	int hsr, ret = 1;
> +	bool writable;
> +	gfn_t gfn;
>  
>  	if (handle_guest_sei((unsigned long)fault_ipa,
>  				kvm_vcpu_get_hsr(vcpu))) {
> @@ -190,9 +194,20 @@ static int kvm_handle_guest_sei(struct kvm_vcpu *vcpu, struct kvm_run *run)
>  				(unsigned long)kvm_vcpu_get_hsr(vcpu));
>  
>  		kvm_inject_vabt(vcpu);
> +	} else {
> +		hsr = kvm_vcpu_get_hsr(vcpu);
> +
> +		gfn = fault_ipa >> PAGE_SHIFT;
> +		memslot = gfn_to_memslot(vcpu->kvm, gfn);
> +		hva = gfn_to_hva_memslot_prot(memslot, gfn, &writable);
> +
> +		run->exit_reason = KVM_EXIT_INTR;
> +		run->intr.syndrome_info = hsr;
> +		run->intr.address = hva;
> +		ret = 0;
>  	}
>  
> -	return 0;
> +	return ret;
>  }
>  
>  /*
> @@ -218,8 +233,7 @@ int handle_exit(struct kvm_vcpu *vcpu, struct kvm_run *run,
>  			*vcpu_pc(vcpu) -= adj;
>  		}
>  
> -		kvm_handle_guest_sei(vcpu, run);
> -		return 1;
> +		return kvm_handle_guest_sei(vcpu, run);
>  	}
>  
>  	exception_index = ARM_EXCEPTION_CODE(exception_index);
> @@ -228,8 +242,7 @@ int handle_exit(struct kvm_vcpu *vcpu, struct kvm_run *run,
>  	case ARM_EXCEPTION_IRQ:
>  		return 1;
>  	case ARM_EXCEPTION_EL1_SERROR:
> -		kvm_handle_guest_sei(vcpu, run);
> -		return 1;
> +		return kvm_handle_guest_sei(vcpu, run);
>  	case ARM_EXCEPTION_TRAP:
>  		/*
>  		 * See ARM ARM B1.14.1: "Hyp traps on instructions
> diff --git a/arch/arm64/kvm/hyp/switch.c b/arch/arm64/kvm/hyp/switch.c
> index aede165..ded6211 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);
> +    /* If virtual System Error or Asynchronous Abort is pending. set

nit: I think you want a comma after pending, not a dot.

> +     * the virtual exception syndrome information
> +     */

nit: commenting style

> +	if (cpus_have_cap(ARM64_HAS_RAS_EXTN) &&
> +			(vcpu->arch.hcr_el2 & HCR_VSE))
> +		write_sysreg_s(vcpu->arch.fault.vsesr_el2, VSESR_EL2);
> +
>  	/* Trap on AArch32 cp15 c15 accesses (EL1 or EL0) */
>  	write_sysreg(1 << 15, hstr_el2);
>  	/*
> @@ -139,9 +146,15 @@ 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);
>  
> +		if (cpus_have_cap(ARM64_HAS_RAS_EXTN)) {
> +			/* set vsesr_el2[24:0] with esr_el2[24:0] */
> +			kvm_vcpu_set_vsesr(vcpu, read_sysreg_el2(esr)
> +					& VSESR_ELx_IDS_ISS_MASK);
> +		}
> +	}
>  	__deactivate_traps_arch()();
>  	write_sysreg(0, hstr_el2);
>  	write_sysreg(0, pmuserenr_el0);
> diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
> index 27fe556..bb02909 100644
> --- a/include/uapi/linux/kvm.h
> +++ b/include/uapi/linux/kvm.h
> @@ -360,6 +360,11 @@ struct kvm_run {
>  		struct {
>  			__u8 vector;
>  		} eoi;
> +		/* KVM_EXIT_INTR */
> +		struct {
> +			__u32 syndrome_info;
> +			__u64 address;
> +		} intr;

definitely, not.  KVM_EXIT_INTR is a generic exit code to tell userspace
that we exited because we needed to deliver a signal or something else
related to an asynchronous event.  This implies that the syndrome_info
etc. always has valid values on all architectures when exiting with
KVM_EXIT_INTR.

Either document the behavior as the syndrome_info has side-channel
information on every exit, or on some KVM_EXIT_INTR exits, as we explain
in the KVM_CAP_ARM_USER_IRQ ABI that was just added, or dedicate an
access code.

>  		/* KVM_EXIT_HYPERV */
>  		struct kvm_hyperv_exit hyperv;
>  		/* Fix the size of the union. */
> -- 
> 2.10.1
> 

I'll look at the details of such patches once the ABI is clear and
well-documented.

Thanks,
-Christoffer