Re: [PATCH v6 3/7] KVM: arm64: Handle DABT caused by LS64* instructions on unsupported memory

[Zhou Wang <wangzhou1@hisilicon.com>]

On 2025/10/25 3:54, Oliver Upton wrote:
> Hi Zhou,
> 
> On Fri, Oct 24, 2025 at 05:08:15PM +0800, Zhou Wang wrote:
>> +/**
>> + * kvm_inject_dabt_excl_atomic - inject a data abort for unsupported exclusive
>> + *				 or atomic access
>> + * @vcpu: The VCPU to receive the data abort
>> + * @addr: The address to report in the DFAR
>> + *
>> + * It is assumed that this code is called from the VCPU thread and that the
>> + * VCPU therefore is not currently executing guest code.
>> + */
>> +void kvm_inject_dabt_excl_atomic(struct kvm_vcpu *vcpu, u64 addr)
>> +{
>> +	u64 esr;
>> +
>> +	/* Reuse the general DABT injection routine and modify the DFSC */
>> +	kvm_inject_sea(vcpu, false, addr);
> 
> This potentially injects a nested SEA which I'm not sure you want. There
> still is an interaction with nested, from DDI0487L.a B2.2.6:
> 
>   For the EL1&0 translation regime, if the atomic instruction is not
>   supported because of the memory type that is defined in the first
>   stage of translation, or the second stage of translation is not
>   enabled, then this exception is a first stage abort and is taken to
>   EL1. Otherwise, the exception is a second stage abort and is taken to EL2.
> 
> We don't need to worry about the S1 memory type since hardware will
> handle that for us. But we do need to consider whether the guest
> hypervisor enabled stage-2 translation or not and route accordingly.
> 
> int kvm_inject_nested_excl_atomic(struct kvm_vcpu *vcpu, u64 addr)
> {
> 	u64 esr = FIELD_PREP(ESR_ELx_EC_MASK, ESR_ELx_EC_DABT_LOW) |
> 		  FIELD_PREP(ESR_ELx_FSC, ESR_ELx_FSC_EXCL_ATOMIC) |
> 		  ESR_ELx_IL;
> 
> 	vcpu_write_sys_reg(vcpu, addr, FAR_EL2);
> 	return kvm_inject_nested_sync(vcpu, esr);
> }
> 
> int kvm_inject_excl_atomic(struct kvm_vcpu *vcpu, u64 addr)
> {
> 	if (is_nested_ctxt(vcpu) && (vcpu_read_sys_reg(vcpu, HCR_EL2) & HCR_VM))
> 		return kvm_inject_nested_excl_atomic(vcpu, addr);
> 
> 	__kvm_inject_sea(vcpu, false, addr);
> 	esr = vcpu_read_sys_reg(vcpu, exception_esr_elx(vcpu));
> 	esr &= ~ESR_ELx_FSC;
> 	esr |= ESR_ELx_FSC_EXCL_ATOMIC;
> 	vcpu_write_sys_reg(vcpu, esr, exception_esr_elx(vcpu));
> 	return 1;
> }

Hi Oliver,

Thanks for pointing this, will modify exception injection with
above code.

Best,
Zhou

> 
> Thanks,
> Oliver
> .