Subject: Re: [PATCH 5/7] KVM: arm64: Move 'invalid syndrome' logic out of io_mem_abort()

From: Marc Zyngier <[email-masked]>
Date: Sun, 26 Jul 2020 12:55:16 +0100

On Fri, 24 Jul 2020 15:35:04 +0100,
Will Deacon <[email-masked]> wrote:
> 
> In preparation for handling stage-2 faults on stage-1 page-table walks
> earlier, move the 'invalid syndrome' logic out of io_mem_abort() and
> into its own function, which can be called from kvm_handle_guest_abort()
> directly.
> 
> Cc: Marc Zyngier <[email-masked]>
> Cc: Quentin Perret <[email-masked]>
> Signed-off-by: Will Deacon <[email-masked]>
> ---
>  arch/arm64/kvm/mmio.c | 22 ----------------------
>  arch/arm64/kvm/mmu.c  | 32 ++++++++++++++++++++++++++++++++
>  2 files changed, 32 insertions(+), 22 deletions(-)
> 
> diff --git a/arch/arm64/kvm/mmio.c b/arch/arm64/kvm/mmio.c
> index b54ea5aa6c06..45a630e480e1 100644
> --- a/arch/arm64/kvm/mmio.c
> +++ b/arch/arm64/kvm/mmio.c
> @@ -136,28 +136,6 @@ int io_mem_abort(struct kvm_vcpu *vcpu, struct kvm_run *run,
>  	int len;
>  	u8 data_buf[8];
>  
> -	/*
> -	 * No valid syndrome? Ask userspace for help if it has
> -	 * volunteered to do so, and bail out otherwise.
> -	 */
> -	if (!kvm_vcpu_dabt_isvalid(vcpu)) {
> -		if (vcpu->kvm->arch.return_nisv_io_abort_to_user) {
> -			run->exit_reason = KVM_EXIT_ARM_NISV;
> -			run->arm_nisv.esr_iss = kvm_vcpu_dabt_iss_nisv_sanitized(vcpu);
> -			run->arm_nisv.fault_ipa = fault_ipa;
> -			return 0;
> -		}
> -
> -		kvm_pr_unimpl("Data abort outside memslots with no valid syndrome info\n");
> -		return -ENOSYS;
> -	}
> -
> -	/* Page table accesses IO mem: tell guest to fix its TTBR */
> -	if (kvm_vcpu_dabt_iss1tw(vcpu)) {
> -		kvm_inject_dabt(vcpu, kvm_vcpu_get_hfar(vcpu));
> -		return 1;
> -	}
> -
>  	/*
>  	 * Prepare MMIO operation. First decode the syndrome data we get
>  	 * from the CPU. Then try if some in-kernel emulation feels
> diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c
> index 73e62d360a36..adb933ecd177 100644
> --- a/arch/arm64/kvm/mmu.c
> +++ b/arch/arm64/kvm/mmu.c
> @@ -2046,6 +2046,20 @@ static void handle_access_fault(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa)
>  		kvm_set_pfn_accessed(pfn);
>  }
>  
> +static int handle_error_invalid_dabt(struct kvm_vcpu *vcpu, struct kvm_run *run,

Nit: why the "_error_"? There isn't any error here, only an awkward
part of the architecture. I'd rather see something like
handle_nisv_dabt(), which matches what this function actually does.

> +				     phys_addr_t fault_ipa)
> +{
> +	if (!vcpu->kvm->arch.return_nisv_io_abort_to_user) {
> +		kvm_pr_unimpl("Data abort outside memslots with no valid syndrome info\n");
> +		return -ENOSYS;
> +	}
> +
> +	run->exit_reason = KVM_EXIT_ARM_NISV;
> +	run->arm_nisv.esr_iss = kvm_vcpu_dabt_iss_nisv_sanitized(vcpu);
> +	run->arm_nisv.fault_ipa = fault_ipa;
> +	return 0;
> +}
> +
>  /**
>   * kvm_handle_guest_abort - handles all 2nd stage aborts
>   * @vcpu:	the VCPU pointer
> @@ -2133,6 +2147,21 @@ int kvm_handle_guest_abort(struct kvm_vcpu *vcpu, struct kvm_run *run)
>  		 * of the page size.
>  		 */
>  		fault_ipa |= kvm_vcpu_get_hfar(vcpu) & ((1 << 12) - 1);
> +
> +		/*
> +		 * No valid syndrome? Ask userspace for help if it has
> +		 * volunteered to do so, and bail out otherwise.
> +		 */
> +		if (!kvm_vcpu_dabt_isvalid(vcpu)) {
> +			ret = handle_error_invalid_dabt(vcpu, run, fault_ipa);
> +			goto out_unlock;
> +		}
> +
> +		if (kvm_vcpu_dabt_iss1tw(vcpu)) {
> +			ret = -ENXIO;
> +			goto out;
> +		}
> +
>  		ret = io_mem_abort(vcpu, run, fault_ipa);
>  		goto out_unlock;
>  	}
> @@ -2153,6 +2182,9 @@ int kvm_handle_guest_abort(struct kvm_vcpu *vcpu, struct kvm_run *run)
>  	if (ret == -ENOEXEC) {
>  		kvm_inject_pabt(vcpu, kvm_vcpu_get_hfar(vcpu));
>  		ret = 1;
> +	} else if (ret == -ENXIO) {
> +		kvm_inject_dabt(vcpu, kvm_vcpu_get_hfar(vcpu));
> +		ret = 1;
>  	}
>  out_unlock:
>  	srcu_read_unlock(&vcpu->kvm->srcu, idx);
> -- 
> 2.28.0.rc0.142.g3c755180ce-goog
> 
> 

Otherwise looks OK.

	M.

-- 
Without deviation from the norm, progress is not possible.

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