Re: [PATCH v4 19/21] KVM: arm64: Handle RAS SErrors from EL2 on guest exit

[Christoffer Dall <cdall@linaro.org>]

On Thu, Oct 19, 2017 at 03:58:05PM +0100, James Morse wrote:
> We expect to have firmware-first handling of RAS SErrors, with errors
> notified via an APEI method. For systems without firmware-first, add
> some minimal handling to KVM.
> 
> There are two ways KVM can take an SError due to a guest, either may be a
> RAS error: we exit the guest due to an SError routed to EL2 by HCR_EL2.AMO,
> or we take an SError from EL2 when we unmask PSTATE.A from __guest_exit.
> 
> The current SError from EL2 code unmasks SError and tries to fence any
> pending SError into a single instruction window. It then leaves SError
> unmasked.
> 
> With the v8.2 RAS Extensions we may take an SError for a 'corrected'
> error, but KVM is only able to handle SError from EL2 if they occur
> during this single instruction window...
> 
> The RAS Extensions give us a new instruction to synchronise and
> consume SErrors. The RAS Extensions document (ARM DDI0587),
> '2.4.1 ESB and Unrecoverable errors' describes ESB as synchronising
> SError interrupts generated by 'instructions, translation table walks,
> hardware updates to the translation tables, and instruction fetches on
> the same PE'. This makes ESB equivalent to KVMs existing
> 'dsb, mrs-daifclr, isb' sequence.
> 
> Use the alternatives to synchronise and consume any SError using ESB
> instead of unmasking and taking the SError. Set ARM_EXIT_WITH_SERROR_BIT
> in the exit_code so that we can restart the vcpu if it turns out this
> SError has no impact on the vcpu.
> 
> Signed-off-by: James Morse <james.morse@arm.com>

Reviewed-by: Christoffer Dall <christoffer.dall@linaro.org>

> 
> ---
> Changes since v3:
>  * Moved that nop out of the firing line
> 
>  arch/arm64/include/asm/kvm_emulate.h |  5 +++++
>  arch/arm64/include/asm/kvm_host.h    |  1 +
>  arch/arm64/kernel/asm-offsets.c      |  1 +
>  arch/arm64/kvm/handle_exit.c         | 10 +++++++++-
>  arch/arm64/kvm/hyp/entry.S           | 13 +++++++++++++
>  5 files changed, 29 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/arm64/include/asm/kvm_emulate.h b/arch/arm64/include/asm/kvm_emulate.h
> index 8a7a838eb17a..8274d16df3cd 100644
> --- a/arch/arm64/include/asm/kvm_emulate.h
> +++ b/arch/arm64/include/asm/kvm_emulate.h
> @@ -173,6 +173,11 @@ static inline phys_addr_t kvm_vcpu_get_fault_ipa(const struct kvm_vcpu *vcpu)
>  	return ((phys_addr_t)vcpu->arch.fault.hpfar_el2 & HPFAR_MASK) << 8;
>  }
>  
> +static inline u64 kvm_vcpu_get_disr(const struct kvm_vcpu *vcpu)
> +{
> +	return vcpu->arch.fault.disr_el1;
> +}
> +
>  static inline u32 kvm_vcpu_hvc_get_imm(const struct kvm_vcpu *vcpu)
>  {
>  	return kvm_vcpu_get_hsr(vcpu) & ESR_ELx_xVC_IMM_MASK;
> diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
> index 97438cc3a9ad..cf5d78ba14b5 100644
> --- a/arch/arm64/include/asm/kvm_host.h
> +++ b/arch/arm64/include/asm/kvm_host.h
> @@ -89,6 +89,7 @@ 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 */
> +	u64 disr_el1;		/* Deferred [SError] Status Register */
>  };
>  
>  /*
> diff --git a/arch/arm64/kernel/asm-offsets.c b/arch/arm64/kernel/asm-offsets.c
> index 71bf088f1e4b..121889c49542 100644
> --- a/arch/arm64/kernel/asm-offsets.c
> +++ b/arch/arm64/kernel/asm-offsets.c
> @@ -130,6 +130,7 @@ int main(void)
>    BLANK();
>  #ifdef CONFIG_KVM_ARM_HOST
>    DEFINE(VCPU_CONTEXT,		offsetof(struct kvm_vcpu, arch.ctxt));
> +  DEFINE(VCPU_FAULT_DISR,	offsetof(struct kvm_vcpu, arch.fault.disr_el1));
>    DEFINE(CPU_GP_REGS,		offsetof(struct kvm_cpu_context, gp_regs));
>    DEFINE(CPU_USER_PT_REGS,	offsetof(struct kvm_regs, regs));
>    DEFINE(CPU_FP_REGS,		offsetof(struct kvm_regs, fp_regs));
> diff --git a/arch/arm64/kvm/handle_exit.c b/arch/arm64/kvm/handle_exit.c
> index 345fdbba6c2e..e1e6cfe7d4d9 100644
> --- a/arch/arm64/kvm/handle_exit.c
> +++ b/arch/arm64/kvm/handle_exit.c
> @@ -23,6 +23,7 @@
>  #include <linux/kvm_host.h>
>  
>  #include <asm/esr.h>
> +#include <asm/exception.h>
>  #include <asm/kvm_asm.h>
>  #include <asm/kvm_coproc.h>
>  #include <asm/kvm_emulate.h>
> @@ -208,7 +209,14 @@ int handle_exit(struct kvm_vcpu *vcpu, struct kvm_run *run,
>  			*vcpu_pc(vcpu) -= adj;
>  		}
>  
> -		kvm_inject_vabt(vcpu);
> +		if (cpus_have_const_cap(ARM64_HAS_RAS_EXTN)) {
> +			u64 disr = kvm_vcpu_get_disr(vcpu);
> +
> +			kvm_handle_guest_serror(vcpu, disr_to_esr(disr));
> +		} else {
> +			kvm_inject_vabt(vcpu);
> +		}
> +
>  		return 1;
>  	}
>  
> diff --git a/arch/arm64/kvm/hyp/entry.S b/arch/arm64/kvm/hyp/entry.S
> index 12ee62d6d410..024c7afc78f8 100644
> --- a/arch/arm64/kvm/hyp/entry.S
> +++ b/arch/arm64/kvm/hyp/entry.S
> @@ -124,6 +124,17 @@ ENTRY(__guest_exit)
>  	// Now restore the host regs
>  	restore_callee_saved_regs x2
>  
> +alternative_if ARM64_HAS_RAS_EXTN
> +	// If we have the RAS extensions we can consume a pending error
> +	// without an unmask-SError and isb.
> +	esb
> +	mrs_s	x2, SYS_DISR_EL1
> +	str	x2, [x1, #(VCPU_FAULT_DISR - VCPU_CONTEXT)]
> +	cbz	x2, 1f
> +	msr_s	SYS_DISR_EL1, xzr
> +	orr	x0, x0, #(1<<ARM_EXIT_WITH_SERROR_BIT)
> +1:	ret
> +alternative_else
>  	// If we have a pending asynchronous abort, now is the
>  	// time to find out. From your VAXorcist book, page 666:
>  	// "Threaten me not, oh Evil one!  For I speak with
> @@ -134,7 +145,9 @@ ENTRY(__guest_exit)
>  	mov	x5, x0
>  
>  	dsb	sy		// Synchronize against in-flight ld/st
> +	nop
>  	msr	daifclr, #4	// Unmask aborts
> +alternative_endif
>  
>  	// This is our single instruction exception window. A pending
>  	// SError is guaranteed to occur at the earliest when we unmask
> -- 
> 2.13.3
>